Mosquito & Vector News

West Nile Virus Detection Continues in Eastern Coachella Valley

From NBC Palm Springs
September 27, 2022

“West Nile virus is and can be a very dangerous disease so we’re telling people right now, just be careful when you go outside,” said Tammy Gordon, Public Information Manager for Coachella Valley Mosquito and Vector Control District. 

At least 100 positive samples of the West Nile virus have been detected in the Coachella Valley so far this year. 

“The current samples that we have are showing the Mecca area, so downtown Mecca. However, we have found samples in La Quinta, South La Quinta,” said Gordon. 

West Nile virus is the leading cause of mosquito-borne disease in the United States, according to the CDC. 

No human cases of the illness have been reported in the Coachella Valley, however, the state of california reports 69 positive cases of the virus this year. 

The virus spreads when a female mosquito bites an infected bird. The carrier mosquito can then transmit the virus to humans. 

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Biology of Vector-borne Diseases six-day course

From The University of Idaho (UI) IHHE

Dear members of the Institute for Health in the Human Ecosystem (IHHE),  

The University of Idaho (UI) IHHE is hosting its annual Biology of Vector-borne Diseases six-day course, Monday through Saturday, June 12-17, 2023, on the UI campus in Moscow, Idaho. This course provides accessible, condensed training and “knowledge networking” for advanced graduate students, postdoctoral fellows, new faculty, and current professionals to ensure competency in basic biology and cutting-edge knowledge for U.S. and global vector-borne diseases of plants, animals, and humans.  

With the support of 30+ internationally recognized faculty, we seek to train the next generation of scientists and professionals to think about vector-borne diseases as interconnected pathosystems and help them to develop effective solutions to current and emerging vector-borne disease threats in complex human ecosystems. 

Applications will be reviewed starting December 1, 2022, and applicants will be notified of their acceptance for the course in spring 2023. Please email chhe@uidaho.edu with any questions 

Please would you/your organization to share our event information 

A link to our event is:  https://www.uidaho.edu/research/entities/ihhe/education/vector-borne-diseases  

Apply here: https://www.uidaho.edu/research/entities/ihhe/education/vector-borne-diseases/application 

 

La Crosse virus is the second-most common virus in the US spread by mosquitoes – and can cause severe neurological damage in rare cases

Posted by Vector and Vector-borne Disease Committee
September 25, 2022

Rebecca Trout Fryxell

Associate Professor of Medical and Veterinary Entomology, University of Tennessee

9 Sep 2022.  The Conversation.  https://theconversation.com/la-crosse-virus-is-the-second-most-common-virus-in-the-us-spread-by-mosquitoes-and-can-cause-severe-neurological-damage-in-rare-cases-184412.

Note:  This recent review describes the impact of La Cross virus (LACV) on human health east of the Mississippi where it is transmitted mostly by Aedes triseriatus and Ae. albopictus.  Unlike West Nile virus this neuroinvasive virus affects children more frequently than the elderly and can result in long lasting sequellae.  LACV is one of several arboviruses within the California encephalitis virus (CEV) serogroup within the family Peribunyaviridae.  Although few cases have been diagnosed and surveillance programs no longer test mosquitoes for these viruses, the type virus for this group, CEV, is endemic to California where it is maintained vertically within Aedes melanimon and Ae. dorsalis populations and amplified by horizontal transmission to rabbits.   Another virus within this serogroup, Jamestown Canyon virus, has been isolated from Culiseta inornata collected in California, but seems to be a human health problem mostly in the upper Midwest. 

One Pasadenan Has Contracted West Nile Virus, And Local Health Officials Are Working To Prevent More Infections

From Pasadena NOW
September 25, 2022

The dangerous West Nile virus (WNV) continues to be detected in mosquito and bird populations in the San  Gabriel Valley and one Pasadena resident is known to have contracted the virus this tear, a city health official said.

Manuel Carmona, Acting Director of the Pasadena Public Health Department, said that as of September 9,  there have been 11 human West Nile vims cases reported in Los Angeles County, including one in  Pasadena. 

Mosquito control experts are advising residents to remove stagnant water due to the early  September rain. The stagnant rainwater sitting in containers can result in a risk of mosquito-borne diseases in the community. 

City officials said that if residents notice any stagnant water issues in their community, they can submit a tip online or call 626-814-9466.  

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‘Drain after rain’ to prevent mosquito breeding

From Fox 40
September 20, 2022

(KTXL) — The Sacramento-Yolo Mosquito and Vector Control District are reminding residents to “drain after the rain” in order to prevent mosquitoes.

According to the Sacramento-Yolo Mosquito and Vector Control District, warm temperatures after rain will create ideal breeding conditions for mosquitoes.

The Sacramento-Yolo Mosquito and Vector Control District said in a news release that mosquito season is not over and the threat of West Nile virus is still being seen in dead birds and mosquito samples across the county. There are 3 confirmed cases of West Nile virus in humans in Yolo County.

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Positive West Nile Virus Mosquitoes Found in Portions of Mountain View, Los Altos Hills and Sunnyvale

From the County of Santa Clara
September 20, 2022

SANTA CLARA COUNTY, CALIF. – The County of Santa Clara Vector Control District has confirmed the presence of West Nile virus-positive mosquitoes in a small area that includes Mountain View, Los Altos Hills and Sunnyvale (ZIP codes 94024, 94040 and 94087). Weather permitting, this area will be treated to reduce adult mosquito populations with the use of truck-mounted equipment on Thursday, Sept. 22, starting around 10 p.m. and concluding a few hours later.
 
The District’s mosquito management program largely focuses on preventing mosquitoes from reaching the adult biting stage by proactively targeting immature stages of mosquitoes found in standing water. When a mosquito with West Nile Virus (WNV) is detected, however, the District takes the added step of conducting adult mosquito control treatment to reduce the mosquito population in the area, which decreases the risk of a WNV-human infection.
 
It is normal to see an increase in West Nile virus during the summer and early fall because mosquitoes thrive in warm weather. Although mosquitoes need water at each stage of life, they are still able to thrive during the drought conditions the state and county are seeing now.

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Positive West Nile Virus Mosquitoes Found in Portions of Milpitas

From the County of Santa Clara
September 19, 2022

SANTA CLARA COUNTY, CALIF. – The County of Santa Clara Vector Control District has confirmed the presence of West Nile virus-positive mosquitoes in a small area of Milpitas (ZIP code 95035). Weather permitting, this area will be treated to reduce adult mosquito populations with the use of truck-mounted equipment on Wednesday, Sept. 21, starting around 10 p.m. and concluding a few hours later.
 
The District’s mosquito management program largely focuses on preventing mosquitoes from reaching the adult biting stage by proactively targeting immature stages of mosquitoes found in standing water. When a mosquito with West Nile Virus (WNV) is detected, however, the District takes the added step of conducting adult mosquito control treatment to reduce the mosquito population in the area, which decreases the risk of a WNV-human infection.
 
It is normal to see an increase in West Nile virus during the summer and early fall because mosquitoes thrive in warm weather. Although mosquitoes need water at each stage of life, they are still able to thrive during the drought conditions the state and county are seeing now.

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Attack Of The Ankle-Biter: Aedes Mosquitos Plague Southern California

From MSN
September 14, 2022

REDONDO BEACH, CA — Residents of Redondo Beach have been pestered by relentless, and frankly annoying, bites from the invasive Aedes mosquito that has made a new home in Southern California.

Atypical to other mosquitos that usually go for just one bite at dawn or dusk, Aedes mosquitos are aggressive and love to bite people during the day according to Aaron Arugay, Executive Director of Los Angeles County West Vector Control.

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First human West Nile virus case of 2022 reported in Shasta County

From the Record Searchlight
September 6, 2022

A Shasta County resident is in the hospital with the West Nile virus, the first reported human case in the county this year, health officials announced Tuesday.

The announcement confirmed the patient is an adult but did not say where they contracted the virus or provide any other identifying information to protect the patient’s privacy.

The first sign of West Nile virus appeared in Redding in early July.

The Shasta Mosquito and Vector Control District said it had found in one of its traps an adult male mosquito that was carrying the disease. 

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Officials confirm 1st human case of West Nile Virus in Madera County this year

From ABC30
September 1, 2022

MADERA COUNTY, Calif. (KFSN) — Health officials have confirmed the first human case of West Nile Virus in Madera County this year.

Officials have not released the person’s condition.

“This case is a reminder of the risks from West Nile Virus-infected mosquito bites. It is important to learn and follow the recommendations to lower your risk of being bitten by mosquitoes,” stated Simon Paul, M.D., Madera County Public Health Officer.

Symptoms include a fever, head or body ache, and joint pain.

But according to the CDC, 8 out of 10 people infected with West Nile won’t develop symptoms.

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Death from West Nile virus reported in Fresno County

From Fresno 26 News
September 1, 2022

The Fresno County Department of Public Health (FCDPH) confirmed a human death caused by West Nile Virus (WNV).

The department has reported nine positive human cases of WNV this year, and that number is expected to increase.

There 14 positive cases and one death reported in Fresno County in 2021.

According to the California Department of Public Health (CDPH) in 2021, there were 129 reported WNV cases in the state, including 12 deaths.

Since WNV was first introduced into California in 2003, there have been more than 7,300 human WNV cases and more than 330 WNV-related deaths across the state.

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Invasive species of mosquito detected in Chico

From KRCR 7
August 31, 2022

The Butte County Mosquito and Vector Control District (MVCD) detected an invasive species of mosquito on Tuesday, Aug. 30, 2022.

Officials said the Yellow Fever Mosquito, (Aedes Mosquito, Ades aegypti) was found in Chico near East Avenue and Manzanita Avenue.

This invasive, non-native species of mosquito has been detected in Butte County for three consecutive years now—in Oroville and now Chico.

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Heat brings longer mosquito season, more West Nile cases to Shasta County

From KRCR 7
August 31, 2022

As excessive, triple-digit temperatures engulf our area, the number of mosquitoes infected with West Nile Virus (WNV) continues to grow.

On Wednesday this week, the Shasta Mosquito and Vector Control District (Shasta MVCD) said they saw WNV-positive mosquito sample levels above what they have seen in the last six years.

Shasta MVCD officials said the continued record drought and warm temperatures will encourage a longer season for mosquitoes and the diseases they carry. Out of the hundreds of samples taken from adult mosquitoes in the area, as of Aug. 26, 30 were found to be positive with WNV.

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Estimating Aedes aegypti (Diptera: Culicidae) Flight Distance: Meta-Data Analysis

Posted by Vector and Vector-borne Disease Committee
August 30, 2022

Thomas C Moore, Heidi E Brown

Department of Epidemiology and Biostatistics, Mel and Enid Zuckerman College of Public Health, University of Arizona, Tucson, AZ, USA

Journal of Medical Entomology, Volume 59, Issue 4, July 2022, Pages 1164–1170, https://doi.org/10.1093/jme/tjac070

Abstract  [shortened]:  To generate a more robust estimate of Ae. aegypti flight distance, we conducted a meta-data analysis with the aims 1) to provide a flight distance measurement and 2) investigate how mosquito flight range can be affected by study design and climatic factors. Published studies were retrieved from public databases and reviewed for mean distance traveled (MDT) or maximum distance traveled measurements of Ae. aegypti. Linear regression was used to assess potential relationships between Ae. aegypti flight distance and factors pertaining to climate, degrees of urbanization, and study design. MDT estimates were pooled from 27 experiments to calculate a weighted MDT of 105.69 m. This study addresses the average flight distance of Ae. aegypti with the intention of informing vector control programs in Ae. aegypti prevalent regions of the world.

Comment:  This review incorporates published data to provide a global estimate of flight range, a parameter critical in understanding potential virus transmission patterns and establishing protocols for containment around imported cases.  Although this information was focused on females, male dispersal data establishes possible infiltration rates into areas treated with the releases of genetically altered males for control. 

First West Nile virus cases reported in Antelope Valley

From the Antelope Valley Press
August 28, 2022 

The first human cases of West Nile virus, this year, have been reported in the Antelope Valley, Los Angeles County Public Health Department officials reported, Thursday.

The Department reported six cases in Los Angeles County, in the Antelope, San Gabriel and San Fernando valleys.

Most of the six people infected were hospitalized for the illness, in late July and early August, according to the report.

Further information as to where the cases were in the Antelope Valley, or how many were here, was not available.

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LA County Announces First Human Cases Of West Nile Virus

From the Los Angeles Patch
August 27, 2022

LOS ANGELES, CA — Los Angeles County health officials have confirmed the county’s first human cases of West Nile virus this year, saying six cases have been identified since late July.

No specifics about the patients were released on Thursday — but according to the county Department of Public Health, the victims live in the Antelope Valley, San Fernando Valley and San Gabriel Valley.

Most of the patients were hospitalized in late July and early August, and all are recovering, according to the county.

“Mosquitoes thrive in hot weather and residents should follow simple steps to reduce their risk of exposure to mosquito-borne diseases, such as West Nile virus,” county Health Officer Dr. Muntu Davis said in a statement.

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Fresno County health officials report 9 human cases of West Nile Virus

From ABC 30
August 26, 2022

FRESNO, Calif. (KFSN) — You might want to take a closer look at any standing water near your home, from planters to unmaintained swimming pools.

“If you see anything that’s wiggling like this, it’s mosquito larvae, dump it out,” says Katherine Ramirez, the scientific education coordinator with Fresno County Mosquito Control.

She adds: “It doesn’t matter the area. We’re finding the virus in all areas. It could be that your neighbor has an unmaintained swimming pool.”

While these aren’t fully grown mosquitoes, Ramirez says mosquitoes are temperature-dependent, so the hotter the temperature the faster the development.

“That’s why its important to check water sources on a daily basis when we have hot temperatures or at least once a week,” she says.

Read more

 

LA County reports 1st cases of West Nile virus in humans for 2022

From ABC7
August 25, 2022

LOS ANGELES (CNS) — Los Angeles County health officials Thursday confirmed the county’s first human cases of West Nile virus this year, saying six cases have been identified since late July.

No specifics about the patients were released, but according to the county Department of Public Health, they live in the Antelope Valley, San Fernando Valley and San Gabriel Valley. Most of the patients were hospitalized in late July and early August, and all are recovering, according to the county.

“Mosquitoes thrive in hot weather and residents should follow simple steps to reduce their risk of exposure to mosquito-borne diseases, such as West Nile virus,” county Health Officer Dr. Muntu Davis said in a statement.

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West Nile Virus numbers rising in Fresno County

From MSN
August 25, 2022

FRESNO COUNTY, Calif. (KSEE/KGPE) – The California Department of Health (CDPH) reported that nine Fresno County residents have tested positive for West Nile Virus (WNV) infections.

Health officials say three of the cases are asymptomatic and were blood donors.

The cases are the first reported in this season and according to CDPH, the Fresno County mosquito control districts have also collected 216 samples of mosquitoes that tested positive for WNV.

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West Nile Virus Surge Detected In Cupertino

From The Cupertino Patch
August 24, 2022

SANTA CLARA COUNTY, CA — As Santa Clara County faces its driest year to date in the past 128 years, county officials say drought conditions are causing a rise in mosquito populations and West Nile virus activity

The Santa Clara County Vector Control District warned this week of an uptick in West Nile virus-infected mosquitos found in a small portion of the county.

The district recently detected infected mosquitos in Sunnyvale and Cupertino in the 94086, 94087 and 95014 zip codes.

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East Bay fighting aggressive invasive mosquito species

From KRON 4
August 18, 2022

MARTINEZ (KRON) – Contra Costa County has identified its first group of invasive mosquito species.

The Contra Costa County Mosquito and Vector Control District is now doing surveillance and treatment in the area where the mosquitos were found in Martinez to make sure they are eliminated before becoming widespread.

Officials say these mosquitoes are very aggressive day biters that can transmit viruses like Zika and the virus that causes Yellow Fever. The species, Aedes aegypti, is originally from West Africa, and was first detected in California in 2014.

Mosquitoes can hide in vegetation and debris which makes it hard to find and eliminate them, so the control district is setting up traps and going door-to-door.

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Despite drought, mosquitoes carrying West Nile found locally

From the Los Altos Town Crier
August 17, 2022

The drought baking California has rendered water-restricting local lawns and yards arid, but mosquitoes have fared well this summer nonetheless. Santa Clara County Vector Control District surveillance identified mosquitoes with West Nile virus in parts of Cupertino and started spraying insecticide to target the insects last week, with similar spraying last month in parts of Sunnyvale, Santa Clara and San Jose.

The county maintains surveillance throughout local cities including Mountain View and Los Altos using carbon dioxide traps – which attract hungry adult mosquitoes seeking the exhalations that indicate a likely mammalian meal – and gravid traps, boxes of standing water baited with the funky aroma of rotting alfalfa to attract pregnant mosquitoes ready to start a new generation. The district also uses light traps – a green metal device with a light bulb and a jar of captured insects at its bottom – to monitor the ambient abundance of mosquitoes in the area, which fluctuates seasonally and tends to rise with warm summer weather.

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West Nile Virus Update: Six More Areas in County Report Positive Samples

From SCV News
August 16, 2022

The Greater Los Angeles County Vector Control District has confirmed 13 additional mosquito samples that tested positive for West Nile virus.

This brings the total number of positive samples within the District’s service area to 76 this year.

This is the first detection of the virus this year in the following communities: Canoga Park, Downey, Eagle Rock, Elysian Valley, Los Angeles city and Winnetka.

West Nile virus is endemic to Los Angeles County, and warm temperatures can increase virus activity and mosquito populations. Visit VectorSurv Maps or WestNile.ca.gov for a comprehensive look at this year’s West Nile virus activity throughout Los Angeles County and Southern California.

Join Mosquito Watch to access online tools and resources such as the DIY Mosquito Source Checklist or request door hangers to be distributed in their community at MosquitoWatch.org.

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Orange County man tests positive for West Nile virus; 1st reported case in county

From ABC 7
August 13, 2022

ORANGE, Calif. (KABC) — Orange County has its first reported case of West Nile virus after a man tested positive this week.

Details surrounding the man’s condition weren’t immediately released. It’s also unclear of what portion of Orange County the resident resides in.

People over age 50 and those with certain medical conditions are at an increased risk of getting the virus, health officials warn.

“West Nile Virus is endemic in Orange County, recurring every year during the summer months and continuing into the fall,” said Deputy County Health Officer Dr. Matthew Zahn. “The best way to avoid West Nile Virus infection is to take precautionary measures to avoid mosquito bites.”

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‘It’s tick season all year round’: Precaution recommended for Sonoma County residents against Lyme disease carrying bugs

From The Press Democrat
August 13, 2022

Former Bay Area news anchor Leslie Griffith died Aug. 10, according to a report by KTVU Channel 2 News. Family members say Griffith had been suffering from Lyme Disease since she was bitten by a tick while living in Oregon in 2015.

In California, the western black-legged ticks — the species that carries the bacterium that causes Lyme disease — have been found in 56 of the state’s 58 counties, including Sonoma County, according to the California Department of Public Health.

Yet officials at the Marin-Sonoma Mosquito and Vector Control District say residents can employ several precautions to avoid ticks outdoors and around their homes.

“In Sonoma County, ticks are actually active year-round,” said Nizza Sequeira, public information officer for Marin-Sonoma Mosquito and Vector Control District.

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Orange County reports this year’s first human case of West Nile virus

From CBS Los Angeles
August 12, 2022

A man who tested positive for West Nile virus infection is the first human case reported in Orange County this year, public health officials said Friday.

The patient was described only as an adult male, and the Orange County Health Care Agency gave no further information about the case or where the man may have contracted the virus. However, no one in Orange County has ever died of West Nile virus, and last year there were just three reported cases of human infection.

West Nile virus has already been detected throughout Los Angeles CountyThree dead crows in North Hills tested positive for the virus, but LA County has not yet reported any human infections.

West Nile virus is spread most often by mosquitos, which can infect humans, birds, horses, and other mammals. Most people who become infected do not become sick, but about 20% will develop flu-like symptoms, including fever, headache, body aches, nausea, fatigue, and sometimes a skin rash. More serious symptoms include neck stiffness, confusion, muscle weakness, and paralysis, but those cases are rare.

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More Mosquitoes Test Positive For West Nile Virus In Contra Costa

From the Martinez, CA Patch
August 12, 2022

CONTRA COSTA COUNTY, CA — More mosquitoes have tested positive for West Nile virus in Contra Costa County, authorities said Friday.

The mosquitoes were collected from a trap in an agricultural area east of Brentwood, according to a news release from the Contra Costa Mosquito & Vector Control District.

A previous group of mosquitoes that tested positive this year for WNV was found in Oakley.

WNV comes from certain birds, mostly crows and jays; mosquitoes become infected after biting an infected bird.

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Epidemiologic and environmental characterization of the re-emergence of St. Louis Encephalitis Virus in California, 2015–2020

Posted by Vector and Vector-borne Disease Committee
August 10, 2022

Mary E. Danforth1, Robert E. Snyder1, Tina Feiszli1, Teal Bullick2, Sharon Messenger2, Carl Hanson2, Kerry Padgett1, Lark L. Coffey3, ChristopherM. Barker3, William K. Reisen3, Vicki L. Kramer1

1 California Department of Public Health, Vector-Borne Disease Section, Richmond and Sacramento, California, 2 California Department of Public Health, Viral and Rickettsial Disease Laboratory, Richmond, California, 3 Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, California, United States of America

PLoS Negl Trop Dis 16(8): e0010664. https://doi.org/10.1371/journal.pntd.0010664

Author summary.   St. Louis encephalitis virus is a mosquito-borne virus that can cause human disease and is found in California, where it was detected every year from 1938 to 2003. However, after

West Nile virus arrived in 2003, St. Louis encephalitis virus was not detected again until 2015, when it re-emerged in Riverside County. From 2015 through 2020, St. Louis encephalitis virus has been detected in mosquito pools and sentinel chicken sera samples in 16 counties and a total of 24 human disease cases have been reported. However, during that same time-period, West Nile virus has been detected in 10 times as many mosquito pools and 60 times as many chicken sera samples across 58 counties and over 2,400 human disease cases have been reported. Although mosquitoes are tested routinely for both viruses, surveillance is not uniform throughout the state, and there has been a steady decline in the use of sentinel chickens. Since St. Louis encephalitis virus patient screening is dependent upon environmental detection, California may be underestimating the incidence of human disease due to this virus.

Note:  Although WNV and SLEV cycle enzootically in basically the same vectors and avian hosts, historically SLEV in California never amplified to the levels documented for WNV.  This may be because SLEV does not elicit elevated viremias in a wide diversity of avian hosts which limit transmission efficiency and therefore amplification.   In addition, recently widespread WNV activity may have ‘immunized’ avian populations against SLEV as well as WNV, because previous infection with WNV produces sterilizing immunity against subsequent infection with SLEV.     

Positive West Nile Virus Mosquitoes Found in Portions of Cupertino

From the County of Santa Clara
August 9, 2022

SANTA CLARA COUNTY, CALIF. – The County of Santa Clara Vector Control District has confirmed the presence of West Nile virus-positive mosquitoes in a small area of Cupertino (ZIP Code 95014). Weather permitting, this area will be treated to reduce adult mosquito populations with the use of truck-mounted equipment on Thursday, August 11, starting around 10 p.m., and concluding a few hours later.

The District’s mosquito management program largely focuses on preventing mosquitoes from reaching adulthood by proactively targeting immature stages of mosquitoes (eggs, larvae, and pupae). When a mosquito with West Nile Virus (WNV) is detected, however, the District takes the added step of conducting a mosquito control treatment to reduce the adult mosquito population in the area, which reduces the risk of a WNV-human infection.

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Vector Control Confirms 28 Additional Positive West Nile Virus Samples

From SCV News
August 9, 2022

The Greater Los Angeles County Vector Control District has confirmed 28 additional mosquito samples that tested positive for West Nile virus.

This brings the total number of positive samples within the District’s service area to 63 this year.

The new positive samples were collected from 11 different communities: Artesia, Cerritos, Hawaiian Gardens, La Habra Heights, Long Beach, Porter Ranch, Rowland Heights, San Fernando, Santa Fe Springs, South Whittier and Tarzana.

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Potentially deadly mosquito found in Contra Costa Co. for the first time

From ABC 7 News
August 6, 2022

MARTINEZ, Calif. (KGO) — On Friday, the Contra Costa Mosquito and Vector Control District announced that an invasive mosquito species has been discovered in the city of Martinez.

Measuring about one-quarter of an inch, with a black body and white stripes, they’re called Aedes aegypti.

According to a press release from the county, Aedes mosquitos are described as being very aggressive day biters that can transmit diseases such as Zika, Yellow and Dengue fevers.

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Yolo County’s 1st human case of West Nile virus in 2022 was found. Here’s what that means

From KCRA3
August 4, 2022

Health officials in Yolo County said Wednesday that the first human case of the mosquito-borne West Nile virus so far this year has been detected in the county.

The person became ill last month and is recovering, officials said. Most people infected with the virus do not show symptoms, but the virus can lead to severe illness for some. Health officials say that people should take precautions to reduce the risk of being bitten by mosquitos who may carry the virus.

“By making regular checks of their yards and draining standing water, people can help cut down on mosquito breeding areas,” Yolo County Health Officer Dr. Aimee Sisson said. “Wearing protective clothing and using insect repellent will also reduce the risk of mosquito bites.”

Here’s what else to know about West Nile virus this year.

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First human case of West Nile virus reported in Butte County

From ABC 7
August 4, 2022

The Butte County Public Health agency (BCPH) confirmed this year’s first human case of West Nile Virus (WNV) infection in Butte County, making this the seventh reported incident of WNV infections in California. The individual who was exposed to the virus “is over 65 years of age and is experiencing a severe WNV illness.”

BCPH reminds residents of Butte County that “WNV is active June through October, with August typically being the peak month”. Mosquitos are seen as the primary carrier of the virus.

Those with the infection “fall into three categories”:

  • Asymptomatic (8 in 10 people)
  • Mild to moderate fever illness with fatigue and body aches (1 in 5 people)
  • Severe illness with neurologic symptoms such as encephalitis or meningitis (less than 1 in 150 people). For those who develop a severe WNV illness, symptoms may last several weeks and some symptoms may be permanent.

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Mosquitoes test positive for West Nile virus in Sunnyvale, Santa Clara, SJ

From KRON 4
August 3, 2022

(BCN) — Four days after Contra Costa County reported mosquitoes carrying West Nile virus, officials in Santa Clara County reported Tuesday that they too have found mosquitoes that have tested positive.

The county’s Vector Control District announced plans to begin spraying insecticide from trucks Thursday night in neighborhoods where virus-positive mosquitoes were found in Sunnyvale, Santa Clara and San Jose, confined to ZIP codes 95054, 94089 and 95002. In a news release, county officials said it is normal to see an increase in infected mosquitoes in the summer as they thrive in the heat, and that such spraying has been conducted regularly since 2003.

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1st human case of West Nile Virus detected in Yolo County

From ABC 10
August 3, 2022

YOLO COUNTY, Calif. — Yolo County health officials have confirmed the first human case of West Nile virus (WNV) in the county.

On Wednesday, the Yolo County Health and Human Services Agency Community Health Branch confirmed the positive result. According to officials, the patient first became ill in July and is recovering from neuroinvasive WNV.

“West Nile virus is spread to people by the bite of a mosquito, and there is a risk of contracting West Nile virus in Yolo County this time of year when mosquitoes are active,” Yolo County Health Officer Dr. Aimee Sisson said.

According to health officials, those infected with WNV typically develop symptoms within two to 14 days of being bitten by the infected mosquito. Symptoms include fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach, and back.

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Colorado Tick Fever Virus in the Far West: Forgotten, but Not Gone

Posted by Vector and Vector-borne Disease Committee
August 2, 2022

Kerry A. Padgett,1 Anne Kjemtrup,1 Mark Novak,1 Jason O. Velez,2 and Nicholas Panella2

1Vector-Borne Disease Section, California Department of Public Health, Sacramento, California, USA.

2Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA.

Vector-Borne and Zoonotic Diseases.    2022.  DOI: 10.1089/vbz.2022.0018

Abstract [condensed].   In the past few decades, reported human cases of Colorado tick fever in the western United States have decreased dramatically.  … This study conducted surveillance for Colorado tick fever virus (CTFV) in Dermacentor ticks in recreational sites in Colorado, Wyoming, and California to determine whether the virus is still present.  Adult Rocky Mountain wood ticks (Dermacentor andersoni), Pacific Coast ticks (Dermacentor occidentalis), and winter ticks (Dermacentor albipictus) were tested by PCR and a subset of PCR-positive D. andersoni ticks (n = 7) were cultured in Vero cells. CTFV-positive Rocky Mountain wood ticks were found in all states: Colorado (58% prevalence), Wyoming (21%), and California (4%). Although no winter ticks tested positive, Pacific Coast ticks tested positive in one county (Siskiyou County, 15% prevalence) and were positive only in a location that also maintained Rocky Mountain wood ticks and golden mantled ground squirrels, a known CTFV host. In summary, although the number of human CTFV cases has declined dramatically, this decrease in reported disease does not appear to be due to the disappearance or even the decline in prevalence of this virus in ticks in historically endemic regions of the country.

Note:  This and related recent studies continue to emphasize the public health importance of multiple tick species.  Although the incidence of human infection has remained low and restricted geographically in California, landscape and climate change have been shown to enhance transmission.

Tulare County confirms human case of St. Louis Encephalitis Virus

From ABC 30
August 2, 2022

TULARE COUNTY, Calif. (KFSN) — Tulare County Public Health has confirmed a human case of St. Louis Encephalitis Virus.

Officials say it’s similar to West Nile, and both are transmitted by the same type of mosquitoes.

Five other cases are under investigation as potential encephalitis or West Nile Virus infections.

Health officials say people infected with encephalitis may show flu-like symptoms, such as a fever or headache, or no symptoms at all.

Severe cases can affect the central nervous system.

Officials want to remind you to drain standing water that could attract breeding mosquitoes.

Use insect repellent and wear long sleeves and pants to avoid getting bitten.

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Positive Case of West Nile Virus Found in Contra Costa County Mosquitoes

From NBC Bay Area
August 1, 2022

Contra Costa County health officials are warning people to be careful after its first positive case of West Nile in a group of mosquitoes. 

Workers with the county’s Mosquito and Vector Control District checked catch basins near the Marsh Fire site looking for any type of mosquito activity Monday.

“We don’t want adult female mosquitoes capable of laying eggs and leading to more mosquitoes flying from here and over to the marsh,” said Nola Woods with the Contra Costa Mosquito and Vector Control District 

She’s referring to the site of the Marsh Fire where more the 200 million gallons of water was pumped onto the site to finally put it out after it burned for a few weeks. 

But the big body of water could potentially serve as the ideal breeding environment for mosquitoes. A cause for concern with the county confirming its first pool of mosquitoes in Oakley carrying West Nile. 

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How to prevent West Nile Virus in Kern County

From 23ABC
August 1, 2022

BAKERSFIELD, Calif. (KERO) — Every year in Kern County people and animals are infected by the West Nile Virus. According to Kern County Public Health in 2019 there were 32 human cases. In 2020 there were eight, in 2021 there were three and so far this year, two confirmed cases.

Officials say there are steps you can take to try and avoid coming in contact with mosquitoes.

“I think if you talk to anyone they’re going to tell you they’ve come into contact with mosquitos and so this is the time where transmission is typically the highest,” explained Michelle Corson, public information officer with the Kern County Public Health.

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West Nile Virus: Mosquitoes Test Positive In Contra Costa County

From the Concord, CA Patch
July 29, 2022

CONTRA COSTA COUNTY, CA — A group of mosquitoes has tested positive for West Nile Virus in Contra Costa County, the Contra Costa County Mosquito and Vector Control District said Friday.

The mosquitoes were collected from a trap in the city of Oakley and marked the first group of mosquitoes to test positive for WNV so far this year in the county.

Certain species of birds may carry WNV. Once a mosquito bites an infected bird, the mosquito can become infected with the ability to transmit WNV to another animal or a person through a single mosquito bite.

Since 2005, 75 people in Contra Costa County have been diagnosed with West Nile virus. In 2006, two people in the county died from the disease.

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High temperatures increase risk of mosquito bites and West Nile virus

From the Lake County News
July 28, 2022

LAKEPORT, Calif. — Mosquitoes are here, despite the drought, and the high temperatures are ideal for both mosquitoes and West Nile virus to thrive.

Although no Lake County mosquitoes have tested positive yet for West Nile virus, or WNV, in 2022, the warm nights mean that the virus will be detected here soon in mosquitoes, dead birds or sentinel chickens.

In California, the number of mosquitoes testing positive for West Nile virus activity increased sharply in the last two weeks.

So far, six California residents have been diagnosed with mosquito-borne illnesses this year.

“Both mosquito and West Nile virus activity increase when the overnight temperatures are 60°F or warmer,” said Jamesina Scott, Ph.D., district manager and research director of the Lake County Vector Control District. “In a dry year like this, many people don’t think about mosquitoes or the diseases they carry, like West Nile or St. Louis encephalitis viruses. The best way to protect yourself is avoid mosquito bites.”

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First case of West Nile for 2022 was reported in Kern County

From 23ABC
July 25, 2022

KERN COUNTY, Calif. (KERO) — Kern Public Health has confirmed the first West Nile infection of the year. West Nile Virus is a disease primarily spread by mosquitoes during the summer there have been 400 local cases since it first arrived in Kern in 2004.

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West Nile virus detected in Northern Vacaville

From ABC10
July 25, 2022

VACAVILLE, Calif. — Vacaville city officials announced on Monday Solano County Public Health detected West Nile virus in the area.

Specifically, health officers said they detected the virus in Northern Vacaville near Gibson Canyon and Browns Valley Parkway.

“Reduce the risk of WNV infection by protecting yourself from mosquito bites,” officials said on Facebook.

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Survival and Release of 5 American Crows (Corvus brachyrhynchos) Naturally Infected With West Nile Virus

Posted by Vector and Vector-borne Disease Committee
July 25, 2022

Cynthia Hopf, Elizabeth Bunting, Anne Clark, and Sara Childs-Sanford        

From the Janet L. Swanson Wildlife Hospital and the Department of Clinical Sciences, College of Veterinary Medicine (Hopf, Childs-Sanford), and the Department of Population Medicine and Diagnostic Sciences (Bunting), Cornell University, Ithaca, NY 14853, USA; and the Department of Biological Sciences, Binghamton University, Binghamton, NY 13902, USA (Clark).

Journal of Avian Medicine and Surgery 36(1), 85-91, (2 May 2022). https://doi.org/10.1647/20-00112

Abstract [condensed].   …  American crows with WNV infections are received and treated at the Janet L. Swanson Wildlife Hospital (Cornell University, Ithaca, NY, USA) on a regular basis during the summer and fall and have historically had a 100% mortality rate. The 5 American crows in this case series were tested, when possible, by polymerase chain reaction (PCR) and plaque reduction neutralization on admission and monitored with both PCR and plaque reduction neutralization throughout their rehabilitation process. Four of the 5 birds had a negative PCR test before release, and 1 bird had a “suspect” positive PCR test result before release. One of the crows was confirmed to have survived for at least 2.5 years after release. Viral shedding was documented up to 93 days after initial hospitalization, which is longer than any previous report of WNV shedding in an American crow.

Note:  The study documents the survival of some crows after infection with WNV.  Expansion of this trend may reduce the sensitivity of the dead bird surveillance program and perhaps attenuate WNV amplification through increasing flock immunity.  

Why are there no human West Nile virus outbreaks in South America?

Posted by Vector and Vector-borne Disease Committee
July 25, 2022

Camila Lorenz,* and Francisco Chiaravalloti-Neto

Department of Epidemiology, School of Public Health, University of S~ao Paulo, S~ao Paulo, Brazil

The Lancet Regional Health – Americas 2022;12: 100276;

Published online:   https://doi.org/10.1016/j.lana.2022.100276

Note:  Historically the North American encephalitis viruses have more or less ‘disappeared’ into the Neotropics, with sporadic detection during enhanced surveillance and small outbreaks documented in Argentina.  The current Comment piece proposes the following hypotheses.  1) Under-reporting.  Diagnosis of WNV fever cases may be lost among the frequent occurrence of other arboviruses such as DENV, ZIKV and Mayaro.   2) Co-circulation.  Other viruses such as Rocio and SLEV may provide cross protection and limit amplification.  However, this would seem poorly supported given the recent resurgence of SLEV in the SW USA where WNV remains endemic.  3) Evolution of attenuated strains.  Several isolates from the Neotropics have been attenuated and may not produce neuroinvasive disease and therefore are not detected.

Yellow fever mosquito detected in Placer County

From FOX 40
July 22, 2022

GRANITE BAY, Calif. (KTXL) — On Tuesday, the Placer County Mosquito and Vector Control District announced that on July 14 Aedes aegypti, yellow fever mosquitos, were found in Granite Bay.

The invasive species was found in a residential area of the community south of Granite Bay High School, according to Placer Mosquito.

“We are following our invasive mosquito response plan to determine the extent of the infestation,” Placer Mosquito General Manager Joel Buettner said in a news release. “We ask residents to help us by allowing our technicians to inspect front and back yards of nearby properties.”

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West Nile virus on the rise in Fresno County. Here’s how you can protect yourself

From the Fresno Bee
July 22, 2022

An increase in West Nile virus-positive mosquitoes prompted officials Friday to issue an alert for Fresno County residents.

Katherine Ramirez of the Consolidated Mosquito Abatement District called the discovery of more virus-carrying insects concerning, and urged people to prevent development of mosquito infestations around their homes.

The district has collected West Nile virus-positive mosquitoes from areas within the cities of Fresno, Clovis, Sanger and Reedley, Ramirez said.

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Valley gets another case of West Nile virus

From the Valley Press
July 22, 2022

LANCASTER — The Valley’s second case of West Nile virus this season has been found in an infected great horned owl, Antelope Valley Mosquito and Vector Control District officials reported, on Thursday.

The owl that tested positive for the virus was found near Avenue H and 30th Street East.

“The owl was alive but ill when it was picked up by a veterinarian and taken to the Ojai Raptor Center for care,” District Entomologist Karen Mellor said in a release. It is reportedly recovering at the center.

District personnel will continue with intensive searches of the area where the owl was found, as well as through the entire District, to keep mosquito populations low and reduce the risk of disease.

The first instance of West Nile virus, this year, was reported, in mid-June, when mosquitos carrying the disease were found in a trap in the vicinity of 40th Street East and Avenue J-8.

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Experimental Rickettsia typhi Infection in Monodelphis domestica: Implications for Opossums as an Amplifying Host in the Suburban Cycle of Murine Typhus

Posted by Vector and Vector-borne Disease Committee
July 20, 2022

Lucas S. Blanton1, Bethany R. Quade1, Alejandro Ramírez-Hernández2, Nicole L. Mendell3, Alejandro Villasante-Tezanos4, Donald H. Bouyer3, John L. VandeBerg5, and David H. Walker3

1 Department of Internal Medicine—Division of Infectious Diseases, University of Texas Medical Branch, Galveston, Texas; | 2 Veterinary Parasitology Research Group, National University of Colombia, Bogotá, Colombia; | 3 Department of Pathology, University of Texas Medical Branch, Galveston, Texas; | 4 Department of Preventive Medicine and Population Health, University of Texas Medical Branch, Galveston, Texas; | 5 Department of Human Genetics, South Texas Diabetes and Obesity Institute, and Center for Vector-Borne Diseases, The University of Texas Rio Grande Valley, Brownsville, Texas

Am. J. Trop. Med. HYg.  107:  102-109;  DOI: https://doi.org/10.4269/ajtmh.21-1076

Abstract:   Murine typhus is an acute undifferentiated febrile illness caused by Rickettsia typhi. In the United States, its reemergence appears to be driven by a shift from the classic rat–rat flea cycle of transmission to one involving opossums (Didelphis virginiana) and cat fleas. Little is known of the ability of opossums to act as a reservoir and amplifying host for R. typhi. Here, we use Monodelphis domestica (the laboratory opossum) as a surrogate for D. virginiana. Opossums were inoculated via the intraperitoneal (IP) or intradermal (ID) route with 1 × 106 viable R. typhi. Blood and tissues were collected on days 6, 13, 20, and 27 or if moribund. Although one ID-infected opossum died, the remainder did not appear ill, whereas half of the IP-inoculated animals succumbed to infection. Rickettsemia was demonstrated in all animals through week 2 of infection and sporadically in weeks 3 and 4. Rickettsia typhi DNA was detected in all tissues, with most animals demonstrating the presence of bacteria into weeks 3 and 4. Akin to infection in rats, the demonstration of disseminated infection, typical inflammation, and prolonged rickettsemia with relatively few clinical effects (especially in the more natural route of ID inoculation) supports the potential of opossums to act as a competent mammalian reservoir and component of the zoonotic maintenance cycle of R. typhi. Understanding the dynamics of infection within opossums may have implications for the prevention and control of murine typhus.

Note:  With the rise in the number of human typhus cases in southern California, this work establishes opossums [an important host of cat fleas] as a critical reservoir for the rickettsia. 

Second Horse Tests Positive for West Nile Virus in California

From The Horse
July 19, 2022

The California Department of Food and Agriculture confirmed a 4-year-old unvaccinated Quarter Horse gelding in Kern County, California, positive for West Nile virus (WNV) on July 11. On July 2, he presented with acute pelvic limb ataxia (incoordination) that progressed to recumbency (down and unable to get up), and fever. The horse has been euthanized due to the severity of his signs. The boarding facility where he resided is not currently under quarantine.

This case marks California’s second confirmed horse with WNV in 2022. 

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