An epidemic of Rocky Mountain spotted fever (RMSF) is ongoing in Mexicali, M éxico. We visited 100 neighborhoods with diagnosed human cases and 100 control neighborhoods to evaluate knowledge of the epidemic; obtain data on the spatial distribution of dogs, canine seroprevalence and active infection, tick infestations, and presence of rickettsial DNA in ticks; and evaluate risk factors for human cases, seropositivity, and tick infestation within an unbiased study design. The majority (80%) of residents had heard of RMSF, but only 48% used acaricides in the home or on dogs. Case neighborhoods and those with high canine seroprevalence tended to be on the city periphery or in the agricultural valley. No dogs were polymerase chain reaction (PCR) positive for Rickettsia rickettsii, and the overall seroprevalence was 65% (titers from 64 to 1,024). PCR prevalence in ticks was 0.70%, confirmed by DNA sequencing as R. rickettsii; neighborhood prevalence ranged from 0.7% to 6.1%. Twelve percent of dogs had high tick burdens, and all ticks were Rhipicephalus sanguineus. Epidemiologically significant risk factors were ground covering for a neighborhood having a human case; dogs having poor body condition and weighing < 10 kg for canine seropositivity; dogs living at the home for the number of ticks in the environment; and being near canals, having trash on the patio, and a dog being thin for tick burdens on dogs. A One Health approach is crucial to understanding RMSF and brown dog ticks.

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Since 2008, a large epidemic of Rocky Mountain spotted fever has been emerging among humans and dogs in Mexicali, adjacent to the United States in Baja California, Mexico. We molecularly confirmed the causative agent; this information can be used to study the origin and dynamics of the epidemic.

ABSTRACT. Zoonotic parasitic infections are a major global public and veterinary health problem and widespread among stray dogs. The objective of this study was to establish the prevalence of intestinal parasites in stray dogs in the urban, rural and coastal areas of Mexicali County in northwest Mexico. In 2014, from January to December, 380 stray dogs were captured. The entire small intestine, cecum and faeces samples were collected and examined by using simple zinc sulfate flotation and Lugol's solution staining. Data were statistically analysed. Overall, about 21.5% of examined dogs were found positive for intestinal parasites. Toxocara canis was the most frequent detected parasite, with a prevalence of 7.1%, followed by Toxascaris leonina (5.5%), Cystoisospora spp. (5.0%), Taenia spp. (3.9%) and Dipylidium caninum (2.8%). Dogs were more frequently found to be infected with a single genus of intestinal parasite (18.7%) than co-infected (2.8%). Intestinal parasites were more prevalent in samples from the coastal area (25%) than in those from the rural (24.4%) and urban (20.6%) areas, however, only statistical association was found between capture area and specific intestinal parasitic infection. There were significant differences in the prevalence of taeniasis among two age groups (P<0.01). A seasonal peak of prevalence for intestinal parasitic infections was found during spring (P<0.05), corresponding with a seasonal peak of prevalence of T. canis (P<0.05). The wide range of isolated parasites indicated that people residing in this area are at risk of exposure to these potentially hazardous zoonotic pathogens.Key words: toxocariasis, taeniasis, Mexico, public health. RESUMEN.Las infecciones zoonóticas parasitarias son un problema global público y para la medicina veterinaria, siendo diseminadas por perros callejeros. El objetivo del estudio fue determinar la prevalencia de parasitosis intestinales en perros callejeros de la zona urbana, rural y costera del municipio de Mexicali, noroeste de México. En 2014, entre enero y diciembre, se capturaron 380 perros. Se colectó el intestino, ciego y heces y se examinaron utilizando flotación con sulfato de zinc y tinción con la solución de Lugol. Los datos fueron analizados estadísticamente. En general, alrededor del 21,5% de los perros examinados fueron positivos a parásitos intestinales. Toxocara canis fue el parásito más frecuentemente, con una prevalencia del 7,1%, seguido por Toxascaris leonina (5,5%), Cystoisospora spp. (5,0%), Taenia spp. (3,9%) y Dipylidium caninum (2,8%). Los perros fueron más frecuentemente encontrados infectados con un solo género de parásito intestinal (18,7%) que coinfectados (2,8%). Las parasitosis intestinales fueron más prevalentes en muestras de la costa (25%) que del área rural (24,4%) y urbana (20,6%), sin embargo solo se encontró asociación estadística entre el área de captura y las parasitosis intestinales específicas. Hubo diferencias significativas en la prevalencia de taeniasis entre los dos grupos de edad (P<0,01). El pico esta...