B.M. Mortola et al. 2025. J. Med. Entomol., tjaf001, https://doi.org/10.1093/jme/tjaf001

Abstract
The evolution of pyrethroid insecticide resistance in Culex tarsalis Coquillett is a growing concern in Northern California. Common mechanisms of resistance include the target-site mutation, kdr, and increased levels of detoxification enzymes, such as mixed-function oxidases, GSTs, and esterases. The goal of this study was to compare the prevalence of kdr mutations (L1014F and L1014S) and detoxification enzymes between pyrethroid susceptible and resistant Cx. tarsalis individuals. Individual mosquitoes, categorized by resistance status from permethrin bottle bioassays, were prepared for both molecular and enzymatic testing by separating the legs of a mosquito from the remaining body. Legs were used to test for the presence of kdr mutations, while the bodies were used to test for the activity of detoxification enzymes. The number of phenylalanine (F) alleles present at the kdr target-site as well as levels of GST were increased in mosquitoes that survived the bottle bioassay compared to those that were knocked down. Individuals with 2 F alleles and an active GST level greater than or equal to 0.052 µg/ml showed a higher survival rate than either mechanism independently demonstrating resistance to pyrethroids in Cx. tarsalis is likely the result of multiple resistance mechanisms acting collectively. Further work is needed to determine the interplay of multiple resistance mechanisms to achieve phenotype resistance in this mosquito species.

Note: Relating bottle assay results to specific resistance mechanisms is an important step in teasing apart the evolution of resistance.

Sebayang, BF, et al. 2025. PLoS Neglected Tropical Diseases https://doi.org/10.1371/journal.pntd.0012856

Abstract Background
The establishment of Aedes albopictus in the Torres Strait Islands in 2005 is a threat to dengue control in the islands and on mainland Australia. Attractive targeted sugar baits (ATSBs) have been proposed as a control strategy for outdoor mosquitoes like Ae. albopictus. The sugar feeding behaviours of Ae. albopictus was studied to ascertain the potential of ATSBs to mitigate the risk of Ae. albopictus invading mainland Australia from the Torres Strait Islands.

Methodology/Principal Findings
Aedes albopictus was sampled by sweep net collections in village and bushland habitats across two islands both in the mornings and afternoons. Samples were analysed to determine adult abundance as well as fructose prevalence and content by cold-anthrone test. Sampling stations were characterised by vegetation surveys and included the prevalence of flowers and fruit, and canopy cover. Among the 6,186 captured Ae. albopictus, the prevalence of fructose was 31.6% ± 1.4 in males and 30.5% ± 1.2 in females, with fructose averaging 62.9 µg (± 1.4) in fructose-positive Ae. albopictus.

Conclusions
Mosquito sex and collection time were associated with the abundance of Ae. albopictus as well as fructose prevalence and content in Ae. albopictus. Male and female Ae. albopictus exhibited sugar abundance and prevalence comparable to studies where ATSBs were effective suggesting that ATSBs could potentially reduce Ae. albopictus populations in the Torres Strait Islands.

Note: This study concluded that Ae. albopictus fed frequently on plant sugar and that ‘attractive targeted sugar baits’ may be useful for population suppression. Similar studies on Cx. tarsalis produced similar results, but developing an attractive bait for control proved problematic.

Date: Fri 7 Feb 2025
Source: PAHO/WHO Epidemiological Alert [edited] https://www.paho.org/en/documents/epidemiological-alert-risk-dengue-outbreaks-due-increased-circulation-denv-3-americas

The occurrence and magnitude of dengue outbreaks are usually associated with the introduction or increase in circulation of a serotype other than the one that previously predominated in an affected region. Given the risk of an increase in the circulation of DENV3 in the southern hemisphere of the Americas Region during the peak dengue season, the Pan American Health Organization / World Health Organization (PAHO/WHO) urges Member States to prepare for a possible increase in cases and ensure early diagnosis and timely care dengue and other arbovirus cases, in order to prevent severe cases and deaths associated with these diseases.

Summary of the situation in the Americas Region
——————————————————–
In 2024, there was a historic increase in dengue cases in the Americas Region with 13 027 747 cases reported by 50 countries and territories. Of this total, 6 906 396 were laboratory confirmed, 22 684 were characterized as severe dengue (0.17%), and 8186 were fatal cases (case fatality rate 0.063%). The countries that reported the highest proportion of cases were Brazil with 10 232 872 cases, Argentina with 581 559 cases, Mexico with 558 846 cases, Colombia with 320 982 cases, and Paraguay with 295 785 cases (1). Note: This detailed update provides country by country updates on the 2024 and present situation. The risk for further travel related cases persists.

L. Backus et al. email: J Foley jefoley@ucdavis.edu DOI: https://doi.org/10.4269/ajtmh.24-0497 

Abstract: A Rocky Mountain spotted fever (RMSF) epidemic has spread through the state of Baja California, Mexico over the last decade and a half, beginning in Mexicali, and subsequently to Tijuana and to Ensenada by 2018. In October of 2022, we surveyed dogs and homes in randomly selected Áreas Geoestadisticas Básicas (AGEBs) with and without reported human cases. Brown dog ticks (Rhipicephalus sanguineus sensu lato) were found on 33.9% of dogs and in the yards of 23.6% of homes. Homes from AGEBs with cases had over a 6-fold increased odds of ticks being present in the yard than AGEBs without reported cases. Both dogs that were permitted to roam and the presence of roaming dogs in the neighborhood were strongly associated with tick infestation of dogs and homes. No ticks or blood samples were polymerase chain reaction-positive for Rickettsia (R.) rickettsii, the causative agent of RMSF, although 54.6% of dogs were seropositive for spotted fever group rickettsiae, and 17.4% were seropositive for typhus group rickettsiae. R. massiliae and R. felis were detected in eight (1.3%) and 29 (4.8%) ticks, respectively; and R. felis was also detected in eight (4.6%) dog blood samples. Although the pathogenic potential of these other rickettsial species and their role in RMSF transmission remains unclear, our data on tick burdens in dogs and homes as risk factors for RMSF exposure provide further support to the pivotal need to reduce tick burdens and the numbers of roaming dogs to successfully manage the RMSF epidemic in northern Mexico.

Note: This paper clearly shows the importance of animal control and the importance of inspecting/quarantining imported dogs.

T.C. Moore, X. Tang, H.E. Brown [<heidibrown@arizona.edu>] Vector-Borne and Zoonotic Diseases https://doi.org/10.1089/vbz.2024.0072

Abstract
Background: Entomological surveillance indices are used to estimate the risk of West Nile virus transmission. To determine when and where to initiate mosquito control activities, integrated vector management programs establish action thresholds based on entomological surveillance indices. Herein, we examine the evidence from studies that investigated the quantitative relationship between entomological surveillance indices and human WNV cases using systematic review methods. Results: Across three databases, 5378 articles were identified. Using the selection criteria, 38 studies were included for study. Most articles explored entomological indices weekly and devised unique geographic scales to aggregate human and/or mosquito data. The most used models were logistic and negative binomial regression. Maximum likelihood estimates (MLEs) and vector index (VI) demonstrated the greatest ratio of number of positive results to number of times tested. Among all selected articles, 35 unique U.S. locations assessed MLE and/or VI. Human WNV infection had a significant association with MLE across 81.25% (13/16) of locations. VI showed successful performance across 80.00% (24/30) sites tested.

Conclusions:
This systematic review identifies methods for quantifying relationships between entomological and human WNV infection data. We found entomological surveillance indices applied to human WNV risk should include a measure of virus presence, such as MLE and VI. Model type and covariates were too variable to identify geographic or species-specific trends, though, when tested, including temperature, land cover, population density, and time improved the model. This study is meant to be informative and designed to assist public health agencies in seasonal WNV preparations but are not meant to be a panacea for all WNV surveillance challenges.

I. Mateescu & S. Lequime. 2025. J. Med. Entomol. 62(1), 19–28 https://doi.org/10.1093/jme/tjae134

Abstract [shortened]. An arthropod’s vectorial capacity summarizes its disease transmission potential. Studies have shown that mosquito-borne pathogens may alter important vectorial capacity traits of their mosquito vectors, thus directly impacting their transmission and epidemic potential. Here, we compile and discuss the evidence supporting dengue-mediated changes in Aedes aegypti (L.) and evaluate whether the observed effects represent an evolved trait manipulation with epidemiological implications. Dengue infection appears to manipulate essential traits that facilitate vector–host contact, such as locomotor activity, host-seeking, and feeding behavior, but the underlying mechanisms are not understood. Conversely, life-history traits relevant to vector population dynamics, such as survival, oviposition, and fecundity, appear to be negatively impacted by dengue virus. However, methodological disparities among studies render comparisons difficult and limit the ability to reach well-supported conclusions. This highlights the need for more standardized methods for research into changes in virus-mediated traits.

Note: This review paper focusses on dengue virus and aegypti, but may be relevant for other mosquito-borne arboviruses.

West Valley Mosquito and Vector Control District recently published their third paper on SIT. The latest paper discusses the efficacy of SIT targeted approach in the control of Aedes aegypti.

Click here to view

Tularemia — United States, 2011-2022. Rich SN, Hinckley AF, Earley A, et al. 2025. MMWR Morb Mortal Wkly Rep. 73(5152):1152-1156. http://dx.doi.org/10.15585/mmwr.mm735152a1

Tularemia is a rare nationally notifiable zoonosis, caused by the tier-1 select agent _Francisella tularensis_, that has been reported from all USA states except Hawaii. Clinical manifestations typically include fever and localized symptoms that vary by route of infection. The case fatality rate of tularemia is typically <2%, but can be higher depending on clinical manifestation and infecting strain. Tularemia is treatable with antimicrobials. During 2011-2022, a total of 47 states reported 2,462 tularemia cases, but 4 central states (Arkansas, Kansas, Missouri, and Oklahoma) accounted for 50% of all reported cases. Note: This report describes the epidemiology of reported cases and brings attention to this bacteria that has been reported infecting more than 250 species of wild and domestic animals. Infection is through insect or tick bites as well as contact with infected wild animals [e.g., cottontail rabbits] or immersion or ingestion of contaminated water. Ticks may be an important reservoir as they can maintain infection transstadially [pathogen remains within the vector from one life stage (“stadium”) to the next] and transovarially [transmission of a pathogen from an organism (as a tick) to its offspring by infection of eggs in its ovary].

Beyers et al. 2025. Evidence of Limited Laboratory Infection of Culex tarsalis (Diptera: Culicidae) by Usutu Virus. Vector-Borne and Zoonotic Diseases 25(1) https://doi.org/10.1089/vbz.2024.0054

Background: Usutu virus (USUV) is an emerging flavivirus, closely related to West Nile virus (WNV), that has spread into Europe from Africa. Since Culex tarsalis Coquillett is an important vector for WNV transmission in the United States, we tested the ability of USUV to replicate in and be transmitted by these mosquitoes. Materials and Methods: USUV was used to infect 3-4 day-old Cx. tarsalis with 5.6 to 7.5 log10 pfu/ml in goose bloodmeals. Saliva, heads, and bodies were collected on day 13 or 14 and analyzed by RT-qPCR for detection for USUV vRNA. Blotting paper punches were also collected daily to assess viral transmissibility. Results: The low and high dose blood meal resulted in 0% and 19.6% of the mosquitoes having established infections, respectively. All of the high dose females had a dissemination of USUV RNA to the heads and none of the filter papers had detectable USUV RNA, but five of the capillary saliva collections were positive, representing 45.5% of the infected mosquitoes.

Conclusions: Limited infection of Cx. tarsalis was observed when exposed to bloodmeals with greater than 10^7 pfu/mL of USUV, indicating this vector is not likely to have a key role in transmission of the virus. Note: USUV caused frequent epiornitics in blackbirds in Europe, but has not produced noticeable human disease, unlike WNV before its introduction into North America.

Clinical and Epidemiological Information Required for Lyme Disease Surveillance in a Low-Incidence State, California 2011–2017. Brummitt et al. 2024. Vector-Borne and Zoonotic Diseases [ahead of print]. https://doi.org/10.1089/vbz.2024.0043

Abstract [shortened]: Background: Between January 1, 2011, and December 31, 2017, over 12,000 case reports of Lyme disease (LD) were submitted to the California Reportable Disease Information Exchange for further investigation. The number of case reports has tripled compared to previous years, emphasizing the need for efficient estimation and classification methods. We evaluated whether estimation procedures can be implemented in a low-incidence state such as California to correctly classify a case of LD.

Objective: This study identified whether a minimum number of variables was sufficient to reliably classify LD cases in California and potentially reduce workload. Methods: To determine the relative value of diagnostic information, we compared five candidate logistic regression models that were used to classify cases based on information that varied in its degree of difficulty for collection. Results: Our results showed that automatically reported data were not sufficient, additional information such as a patient’s clinical presentation and travel history were necessary to improve the sensitivity of the models. Conclusion: This study demonstrated that both clinical and travel information were required to accurately classify a case of LD in California.

Note: These results were critical to interpret data from a passive case surveillance system to identify areas of high risk endemic transmission.

A scoping review to determine if adverse human health effects are associated with use of organophosphates for mosquito control. Tai, Z. et al. 2024. Journal of Medical Entomology, 2024, 1–11.

https://doi.org/10.1093/jme/tjae130

Abstract [shortened]. Organophosphate insecticides are widely used for adult mosquito control. Although proven effective in reducing mosquito populations and limiting arbovirus transmission, public concern exists regarding potential human health effects associated with organophosphate exposure. The aim of this scoping review was to describe any reported human health conditions associated with organophosphates during their use for adult mosquito control in the United States and Canada. Original peer-reviewed articles published in English language journals from 1 January 2000 to 22 May 2024 identified 6,154 screened articles. Following an independent review, 10 studies were identified that described human health conditions associated with organophosphate exposure during adult mosquito control applications. Of the 10 included studies, only two articles were published within the last 11 years (2013 to 22 May 2024). The included studies could not determine causality between exposure to adulticides and development of illness or adverse impacts. The available and limited evidence indicates that organophosphates can be used safely to control nuisance mosquitoes or mosquitoes that transmit arboviruses. Continued research regarding the human health effects associated with organophosphate applications for adult mosquito control could help evaluate the basis of the public’s concerns and inform public health decision-making.

Malson,M. [downloaded: 30 Nov 24] https://www.bovinevetonline.com/news/education/new-world-screwworm-latest-update-usda-aphis

[Abbreviated]
On Nov. 25, USDA’s Animal and Plant Health Inspection Service (APHIS) held a meeting to discuss the U.S. response to the news of a single case of New World Screwworm (NWS) found in a cow in Chiapas, Mexico. U.S. and Mexican officials are working closely together, but the border has been temporarily closed to live cattle imports.

“Our priority is to ensure there is no risk to our domestic industry, followed by the goal of reopening the border as soon as possible,” says Dr. Michael Watson, administrator of USDA’s APHIS.

In September, work had already begun on protocols in the event NWS was found in Mexico. Those protocols have been reviewed with Mexico for their understanding and will be made public once finalized.

Points of Protocol

Dr. Burke Healey, senior leader for policy and operations for APHIS, shared protocol will likely include pre-export inspections by Mexican veterinarians overseen by SENASICA, the equivalent to APHIS, before allowing cattle imports to resume. The inspections will make sure:

– appropriate logs accompany animals coming into and leaving the facility cattle are treated with ivermectin

– there’s a seven-day quarantine period

Upon passing inspection, cattle will again be inspected by U.S. officials, along with additional inspections for tuberculosis and ticks. The cattle will be dipped, and then presented to cross the border. Healey says federal inspection sites will focus on ports in Chihuahua and Sonora. “Those five ports are on the Mexican side, so those inspections and all of that protocol are taking place in Mexico and not on U.S. soil,” he explains.

Mexico has not completed its investigation, but acknowledges the infested cow might have been imported from Guatemala. While the timeline for reopening trade is tentatively estimated to be at least three weeks, it quite possibly could extend into January as Mexico typically closes ports for two weeks during Christmas and New Year’s, Healey says.

The U.S. imports 1 million to 1.1 million cattle from Mexico annually. All Mexican cattle are required to have a Mexican origin ear tag and documentation of the herd of origin, TB test of that herd of origin and a TB test of the specific animals being presented for export. These requirements will remain in place.

Sterile flies from a Panama facility will be sent to Mexico to help control the spread of NWS further south and into Central America. Capacity from that facility is around 95 million per week. Mexico is also looking at retrofitting fruit fly plants to produce about 60 million sterile files a week.

Note: The continued release of millions of sterile males from a mass production facility in Panama supported by the USDA historically established a barrier for these flies at the Darian Gap. However, recently the flies have bridged this barrier and re-established infestations in Guatemala, perhaps in association with uncontrolled migrant convoys. This has triggered the increase in sterile fly production and releases, but has not eliminated this population. Historically, the screwworm was eradicated in Guatemala and Belize in 1994, El Salvador in 1995, and Honduras in 1996.

Louis, S. et. al. 2024. Emerg Inf Dis 30(12). DOI: https://doi.org/10.3201/eid3012.240655.

Abstract
In a US survey of infectious disease specialists, 61 respondents reported seeing >1 Bartonella quintana [‘trench fever’] infection during 2014–2024. Diagnostic challenges included limited healthcare provider awareness, inadequate testing, and inconsistent healthcare access among affected populations. Early recognition of B. quintana infections is needed to improve outcomes among affected populations. Note: This letter extends previous findings in California by CDPH reporting the isolation of this pathogen from body lice collected from the homeless and serves as a reminder of the importance of providing basic health care and sanitation for all members of society.

A ProMED-mail post

http://www.promedmail.org

ProMED-mail is a program of the International Society for Infectious Diseases http://www.isid.org

Date: Tue 19 Nov 2024 16:20 ET Source: CNN Spanish [in Spanish, trans. Mod.TY, edited] https://cnnespanol.cnn.com/2024/11/19/alerta-puerto-rico-aumento-dengue-orix

The Puerto Rico Department of Health (DSPR) reported on Sunday [17 Nov 2024] that the number of confirmed positive cases of dengue on the island so far in 2024 is 4798, a significant increase of more than triple compared to 2023, when 1242 were recorded.

In a press release, the DSPR indicated that “to date, 9 deaths have been confirmed and an additional one is under investigation.”

“The Department of Health has implemented all the necessary tools to deal with this situation. It is fundamental that communities commit to eliminating mosquito breeding sites, using repellent and protecting themselves from bites. Without citizen participation, it is impossible to contain this epidemic,” said Dr. Carlos Mellado, Secretary of Health, in the letter.

The Puerto Rico Department of Health explained that mosquito repellents have been given to people at mass events and training has been conducted for field health professionals, in addition to updating the guide for ordering dengue diagnostic tests.

Among the municipalities with the highest incidence are San Juan with 995 cases, followed by Carolina with 293 and Rincón with 240. The most affected age groups are people from 40 to 59 years old (936 cases), adolescents from 15 to 19 years old (737), and children from 10 to 14 years old (683), the statement said.

Last March [2024], the department had issued a public health emergency declaration for dengue because the reported cases were at historic levels. At that time, 549 cases of dengue had been recorded.

Note: An advanced warning for those planning to attend the 2025 AMCA meeting in San Juan. All the hurricanes and rain this winter may extend these case numbers by March. Bring repellent!

Cardenas, R. et al. 2024. Med Vet Entomol. 2024;1–14. DOI: 10.1111/mve.12776 Abstract [Shiortened]. Ground water tanks are known to be preferred Aedes aegypti oviposition places providing opportunities for adult and larvae control. A dual-effect insecticidal coating (IC) (alphacypermethrin/ pyriproxyfen) with a slow-release mechanism represents a promising option. Bioassays were designed to determine the mortality and sterilizing effects on gravid mosquitoes exposed to IC. The inhibition of emergence was evaluated in eggs, larvae and pupae exposed in different containers. For the water safety assessment con-centrations of active ingredients were determined by reverse phase high performance liquid chromatography (RP-HPLC) and the health risk was calculated. The IC applied to the interior walls of water-holding containers showed efficacy against Ae. aegypti in terms of high gravid-female mortality (81% at 24 h, p < 0.01), sterilizing effect (inhibition of oviposition by 63%, p < 0.01) and emergence inhibition (100% in eggs, L3 and L4; 97% in pupae). Emergence inhibition was recorded up to 12 months and adult mortality >80%up to 6 months. The use of water stored in treated containers, either for washing or drinking, is not expected to pose a health risk to users. IC applied to domestic water containers has dual and complementary action that reduces Ae. aegypti densities (immature and adult stages).

Note: This approach could be useful in problem underground storm water systems as well as electrical vaults in California.

HLC Dutra, et al. PLoS Negl Trop Dis 18(9): e0012482. https://doi.org/10.1371/journal.pntd.0012482

Abstract Background: We sought to understand how ambient temperature and larval densities in the immature aquatic phases determine adult life history traits and dengue virus loads post-infection. We predicted that larval crowding and high temperatures would both lead to smaller mosquitoes that might struggle to invest in an immune response and, hence, would exhibit high viral loads. Methods. We first examined larval densities from urban and rural areas via a meta-analysis. We then used these data to inform a laboratory-based 2×2 design examining the interacting effects of temperature (21 vs. 26˚C) and density (0.2 vs. 0.4 larvae/mL) on adult life history and dengue virus loads. Results. We found that urban areas had an ~8-fold increase in larval densities compared to more rural sites. Crowding led to slower development, smaller mosquitoes, less survival, lower fecundity, and higher viral loads. The higher temperature led to faster development, reduced fecundity, and lower viral loads. The virus-reducing effect of higher temperature rearing was, however, overwhelmed by the impact of larval crowding when both factors were present. Conclusions. These data reveal complex interactions between the environmental effects experienced by immature mosquitoes and adult traits. They especially highlight the importance of crowding with respect to adult viral loads. Together, these data suggest that urban environments might enhance dengue virus loads and, therefore, possibly transmission, a concerning result given the increasing rates of urbanization globally.

F. Rubino and J. Foley Vector-Borne and Zoonotic Diseases Vol. 24, No. 11

https://doi.org/10.1089/vbz.2024.0012

Abstract Background: This study aimed to compare the exposure histories to ticks and tick-borne pathogens, knowledge, and prevention practices between individuals engaged in fire-related forest management and those participating in recreational activities within Santa Cruz County, CA, in an area of high risk of tick exposure. Methods: Blood samples from 55 forest workers and 58 members of the public were tested for bacterial DNA of and antibodies to Borrelia burgdorferi, Anaplasma phagocytophilum, and Rickettsia species. In addition, a questionnaire was administered to 54 workers and 84 members of the public to identify gaps in knowledge and prevention practices. Results: Although workers had a higher percentage of positive B. burgdorferi antibodies than the public (5.5% compared with 1.7%), the difference was not statistically significant. Conversely, rickettsial antibodies were more prevalent among the public (17.2% versus 3.6% for workers), but specificity to pathogenic bacteria could not be confirmed. No DNA for the three pathogens or antibodies against A. phagocytophilum were detected. Many workers and members of the public reported tick bites (67.4% of participants), with a notable 11% increase among workers in the odds of being bitten for each additional year spent working in forests. Although workers took greater precautions, significant knowledge and practice gaps were identified among both populations, such as an inability to distinguish tick species from common arthropods (mites, spiders, fleas), overestimating the size of ticks, and inappropriate tick-removal techniques. Conclusion: This study underscores the risk of tick-borne diseases faced by fire management workers in Lyme disease–endemic regions. The findings emphasize the necessity for future studies of Lyme disease within this population, and highlight the urgent need for enhanced training programs to minimize these risks.