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.