Urban foci of murine typhus involving cat fleas (Ctenocephalides felis felis) collected from opossums in Mexico City

Vector biology of the cat flea Ctenocephalides felis

Ctenocephalides felis, the cat flea, is among the most prevalent and widely dispersed vectors worldwide. Unfortunately, research on C. felis and associated pathogens (Bartonella and Rickettsia spp.) lags behind that of other vectors and vector-borne pathogens. Therefore, we aimed to review fundamental aspects of C. felis as a vector (behavior, epidemiology, phylogenetics, immunology, and microbiome composition) with an emphasis on key techniques and research avenues employed in other vector species. Future laboratory C. felis experimental infections with Bartonella, Rickettsia, and Wolbachia species/strains should examine the vector-pathogen interface utilizing contemporary visualization, transcriptomic, and gene-editing techniques. Further environmental sampling will inform the range and prevalence of C. felis and associated pathogens, improving the accuracy of vector and pathogen modeling to improve infection/infestation risk assessment and diagnostic recommendations.

Murine Typhus: A Review of a Reemerging Flea-Borne Rickettsiosis with Potential for Neurologic Manifestations and Sequalae

Murine typhus is an acute febrile illness caused by Rickettsia typhi, an obligately intracellular Gram-negative coccobacillus. Rats (Rattus species) and their fleas (Xenopsylla cheopis) serve as the reservoir and vector of R. typhi, respectively. Humans become infected when R. typhi-infected flea feces are rubbed into flea bite wounds or onto mucous membranes. The disease is endemic throughout much of the world, especially in tropical and subtropical seaboard regions where rats are common. Murine typhus is reemerging as an important cause of febrile illness in Texas and Southern California, where an alternate transmission cycle likely involves opossums (Didelphis virginiana) and cat fleas (Ctenocephalides felis). Although primarily an undifferentiated febrile illness, a range of neurologic manifestations may occur, especially when treatment is delayed. Serology is the mainstay of diagnostic testing, but confirmation usually requires demonstrating seroconversion or a fourfold increase in antibody titer from acute- and convalescent-phase sera (antibodies are seldom detectable in the first week of illness). Thus, early empiric treatment with doxycycline, the drug of choice, is imperative. The purpose of this review is to highlight murine typhus as an important emerging and reemerging infectious disease, review its neurologic manifestations, and discuss areas in need of further study.

Confirmation of the presence of Rickettsia felis infecting Ornithodoros puertoricensis in Mexico

Soft ticks are neglected competent vectors of a wide range of pathogenic microorganisms, among which bacteria of the genera Rickettsia and Borrelia stand out. In Mexico, previous studies have shown the presence of a member of the Ornithodoros talaje complex in the Virginia opossum (Didelphis virginiana Didelphimorphia: Didelphidae Kerr) from southeastern Mexico. However, its specific identification has not been achieved. Two D. virginiana were treated in a private clinic during the period of April-May 2022. Tick larvae were manually removed, DNA extraction was performed, and some genes from various bacterial and parasitic pathogens were amplified and sequenced. A total of 96 larvae were recovered, which were morphologically identified as Ornithodoros puertoricensis (Ixodida: Argasidae Fox); the 16 S sequences showed a similarity of 96.79%-99.51% with sequences of O. puertoricensis from Panama and Colombia. The presence of Rickettsia felis (Rickettsiales: Rickettsiaceae Bouyer et al.) was detected in 15 specimens from one host. The soft tick O. puertoricensis is recorded for the first time as an ectoparasite of the Virginia opossum in America and represents the second report for this soft tick in Mexico since 1963. This represents the most northern record of this tick species in its geographic distribution and brings a new soft tick-Rickettsia association.

Effect of urbanization on the opossum Didelphis virginiana health and implications for zoonotic diseases

Urban animals can be an important threat to human health as possible hosts of zoonotic diseases and their susceptibility to these diseases can depend on their overall health conditions. Thus, it is important to understand the factors that determine their health conditions. For this, we studied Virginia opossums (Didelphis virginiana) in six locations with different urbanization levels and types in Mexico City, Mexico. We trapped opossums and measured eight health-related characteristics (number of ectoparasites and tartar severity, among others) and estimated the percentage of area covered by the four main types of terrain (natural vegetation, managed vegetation, impermeable terrain and constructions). Data were analyzed by a canonical correspondence analysis. We found that impermeable terrain was related to negative health characteristics, while the constructions were opposite to impermeable terrain and mostly related to good health characteristics. At the same, time constructed areas held a smaller population than the natural areas. This suggests that constructed areas provide few shelters, but opossums are healthier there, while impermeable areas provide more shelter but cause more health problems to the animals, thus increasing the chances of zoonotic diseases. We recommend reducing the impermeable areas in city planning to contribute to a better health of the urban animals and therefore reduce risks of zoonotic diseases with potentially disastrous results.

Rediscovering an old friend: the case of Ixodes dampfi in a protected natural reserve in central Mexico

The tick Ixodes dampfi Cooley 1943, a member of the Pholeoixodes subgenus, was first described from gophers (Geomys sp.) collected in the state of Mexico. However, information on the origin and parasite-host association of I. dampfi is lacking. Here, new records of the occurrence of this tick species were provided nearly 80 years since its original description, in addition to new localities, genetic data, and host-parasite records. A total of four hosts (one Bassariscus astutus, two Didelphis virginiana, and one Peromyscus gratus) from three orders (Carnivora, Didelphimorphia, and Rodentia) were parasitised by seven I. dampfi females. Sequences of the 16S rDNA gene from the ticks exhibited a similarity ranging from 97 (389/403 bp) to 100% (403/403 bp), with the unique sequence of I. dampfi available on GenBank (AF549837). Additionally, Rickettsia-specific 16S rDNA, htrA, and ompA gene assays generated sequences in four of the seven I. dampfi specimens (57.14%). Partial sequences revealed 99-100% genetic identities with Candidatus Rickettsia angustus (GenBank accession HF935069, HF935072, HF935078) and Candidatus Rickettsia kingi (GenBank accession HF935068, HF935071, HF935077) from Canada. Our results represent the first record of this elusive ectoparasite in a natural protected area, which is a triumph for conservation, as accelerated defaunation processes pose the risk of coextinction for many groups of vertebrates and their ectoparasites.