Prevalence and Phylogenetic Analysis of Bartonella Species of Wild Carnivores and Their Fleas in Northwestern Mexico.

The host-parasite-vector relationship of Bartonella spp. system in wild carnivores and their fleas from northwestern Mexico was investigated. Sixty-six carnivores belonging to eight species were sampled, and 285 fleas belonging to three species were collected during spring (April-May) and fall (October-November) seasons. We detected Bartonella species in 7 carnivores (10.6%) and 27 fleas (9.5%) through either blood culture or PCR. Of the 27 Bartonella-positive fleas, twenty-two were Pulex simulans, three were Pulex irritans and one was Echidnophaga gallinacea. The gltA gene and ITS region sequences alignment revealed six and eight genetic variants of Bartonella spp., respectively. These variants were clustered into Bartonella rochalimae, Bartonella vinsonii subsp. berkhoffii and another genotype, which likely represents a novel species of Bartonella spp. Although experimental infection studies are required to prove the vector role of P. simulans, our results suggest that this flea may play an important role in the Bartonella transmission. The results indicated possible host-specific relationships between Bartonella genotypes and the families of the carnivores, but further studies are needed to verify this finding. The presence of zoonotic species of Bartonella spp. in wild carnivores raises the issue of their potential risk for humans in fragmented ecosystems.

An outbreak of plague including cases with probable pneumonic infection, Ecuador, 1998.

During February and March of 1998, 12 sudden deaths were reported among residents of a high-Andean community in Ecuador. All 12 fatalities were members of the same extended family and some had apparent exposure to sick guinea-pigs. Following an initial investigation by public health officials, an additional death was reported in a nearby community in April, also associated with exposure to sick guinea-pigs. Blood samples from humans, dogs, and a rodent were tested for antibody to the F1 antigen of Yersinia pestis by passive haemagglutination assay. Tissue from rodents was subjected to direct fluorescent antibody staining using fluorescein-labelled monoclonal antibody to Y. pestis F1 antigen. Formalin-fixed specimens from the 2 autopsies were evaluated using a 2-step alkaline phosphatase immunoassay with a monoclonal antibody to Y. pestis F1 antigen, and tissues that had not been embedded in paraffin were tested for the presence of DNA encoding the F1 structural antigen by polymerase chain reaction. Serological evaluation of close contacts of the fatalities revealed positive titres to F1 antigen of Y. pestis, the aetiological agent of plague, in 3 contacts from the first community and 1 from the second. Immunohistochemical staining of tissues collected from 2 of the fatalities provided evidence that both had pneumonic plague. Five of 14 dogs found in the communities were seropositive for plague antibody, providing evidence of a recent epizootic plague in the area.

Incidence of plague associated with increased winter-spring precipitation in New Mexico.

Plague occurs episodically in many parts of the world, and some outbreaks appear to be related to increased abundance of rodents and other mammals that serve as hosts for vector fleas. Climate dynamics may influence the abundance of both fleas and mammals, thereby having an indirect effect on human plague incidence. An understanding of the relationship between climate and plague could be useful in predicting periods of increased risk of plague transmission. In this study, we used correlation analyses of 215 human cases of plague in relation to precipitation records from 1948 to 1996 in areas of New Mexico with history of human plague cases (38 cities, towns, and villages). We conducted analyses using 3 spatial scales: global (El Niño-Southern Oscillation Indices [SOI]); regional (pooled state-wide precipitation averages); and local (precipitation data from weather stations near plague case sites). We found that human plague cases in New Mexico occurred more frequently following winter-spring periods (October to May) with above-average precipitation (mean plague years = 113% of normal rain/ snowfall), resulting in 60% more cases of plague in humans following wet versus dry winter-spring periods. However, we obtained significant results at local level only; regional state-wide precipitation averages and SOI values exhibited no significant correlations to incidence of human plague cases. These results are consistent with our hypothesis of a trophic cascade in which increased winter-spring precipitation enhances small mammal food resource productivity (plants and insects), leading to an increase in the abundance of plague hosts. In addition, moister climate conditions may act to promote flea survival and reproduction, also enhancing plague transmission. Finally, the result that the number of human plague cases in New Mexico was positively associated with higher than normal winter-spring precipitation at a local scale can be used by physicians and public health personnel to identify and predict periods of increased risk of plague transmission to humans.

Discovery of an enzootic cycle of Borrelia burgdorferi in Neotoma mexicana and Ixodes spinipalpis from northern Colorado, an area where Lyme disease is nonendemic.

An intensive enzootic cycle of Borrelia burgdorferi was seen in populations of the Mexican wood rat, Neotoma mexicana, and Ixodes spinipalpis ticks in northern Colorado. Cultures of rodent ear tissue and ticks yielded 63 spirochetal isolates: 38 N. mexicana, 2 Peromyscus difficilis, and 23 I. spinipalpis. All 63 isolates were identified as B. burgdorferi sensu lato by polymerase chain reaction; a representative subset was characterized as B. burgdorferi by SDS-PAGE and immunoblotting. A tick-derived spirochete isolate was infectious to laboratory mice and I. scapularis, the principal vector of Lyme disease in endemic areas of the United States. The risk of human contact with infected I. spinipalpis appears to be minimal from this epidemiologically silent focus in northern Colorado, since this tick is restricted to wood rat nests in this semiarid environment.