Morphological and molecular identification of the brown dog tick in Mexico.

Ticks of the Rhipicephalus sanguineus complex are known as the brown dog ticks. This complex groups at least 12 species of ticks that are distributed worldwide. On the American continents, R. sanguineus sensu stricto (s.s.), is distributed in temperate areas, while Rhipicephalus sanguineus sensu lato (s.l.), also called "tropical lineage" is distributed in tropical regions. Previous analyses of brown dog ticks from Mexico have identified the so-called tropical lineage and the country generally has a climate more favorable for these ticks (> 20o C in average). In addition, some pathogens thought to be transmitted by this lineage (such as Ehrlichia canis, and Rickettsia rickettsii) are prevalent in Mexico. Herein we aim to contribute to the study of brown dog ticks by providing morphological identification and molecular analysis of mt 12S rDNA and 16S rDNA sequences from ticks collected from 12 states in Mexico. Our results indicate that the tropical lineage of R. sanguineus s.l., recently redescribed as R. linnaei is widely distributed in Mexico.

Murine typhus and other potentially lethal rickettsial diseases in Chiapas, Mexico.

Not available.

Development and validation of a novel detection method for Rickettsia rickettsii using a loop-mediated isothermal amplification assay.

Introduction: Rickettsia rickettsii is an obligate, intracellular pathogen and the causative agent of Rocky Mountain spotted fever (RMSF). RMSF is an important zoonotic disease due to its high fatal outcome in humans. The difficulty of clinical diagnosis due to the low sensitivity and specificity of current diagnostic methods are a principal setback. We reported the development of a new method for the detection of R. rickettsii in human and tick DNA samples using loop-mediated isothermal amplification (LAMP), as well as the validation of the LAMP test for R. rickettsii in field samples of infected ticks and humans, determining the diagnostic sensitivity and specificity, as well as the reproducibility of the test. Methods: This technique uses hydroxy naphthol blue (HNB) as an indicator of the formation of magnesium pyrophosphate, a marker for the presence of DNA. Here, we used a putative R. rickettsii gene as a target for three pairs of primers that specifically amplify R. rickettsii DNA by hairpin-based isothermal amplification technique (LAMP). Results and discussion: The sensitivity of the assay was ~1.6-3 pg, which is 10 times more sensitive than PCR. To determine the diagnostics specificity and sensitivity, 103 human DNA samples and 30 tick DNA samples were evaluated. For the human samples, a sensitivity for HNB of 93%, a specificity of 70% and a k of 0.53 were obtained. For electrophoresis the sensitivity was 97% with a specificity of 58% and a k of 0.42. For tick samples, a sensitivity of 80% was obtained, a specificity of 93% for HNB and for electrophoresis the sensitivity and specificity were 87%. The k for both was 0.73. The degree of concordance between HNB and electrophoresis was 0.82 for humans and for ticks, it was 0.87. The result is obtained in shorter time, compared to a PCR protocol, and is visually interpreted by the color change. Therefore, this method could be a reliable tool for the early diagnosis of rickettsiosis.

The genus Rickettsia in Mexico: Current knowledge and perspectives.

The genus Rickettsia encompasses 35 valid species of intracellular, coccobacilli bacteria that can infect several eukaryotic taxa, causing multiple emerging and re-emerging diseases worldwide. This work aimed to gather and summarise the current knowledge about the genus Rickettsia in Mexico, updating the taxonomy of the bacteria and their hosts by including all the records available until 2020, to elucidate host-parasite relationships and determine the geographical distribution of each Rickettsia species present in the country. Until now, 14 species of Rickettsia belonging to four groups have been recorded in Mexico. These species have been associated with 26 arthropod species (14 hard ticks, three soft ticks, two sucking lice, and seven fleas) and 17 mammal species distributed over 30 states in Mexico. This work highlights the high biological inventory of rickettsias for Mexico and reinforces the need to approach the study of this group from a One Health perspective.

Unbiased Assessment of Abundance of Rhipicephalus sanguineus sensu lato Ticks, Canine Exposure to Spotted Fever Group Rickettsia, and Risk Factors in Mexicali, México.

An epidemic of Rocky Mountain spotted fever (RMSF) is ongoing in Mexicali, México. 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.

Molecular Confirmation of Rocky Mountain Spotted Fever Epidemic Agent in Mexicali, Mexico.

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.

[Seroprevalence of risk factors associated with rickettsiosis (Rickettsia rickettsii) in humans in Baja California, Mexico]. / Seroprevalencia y factores de riesgo asociados a riquetsiosis (Rickettsia rickettsii) en humanos de Ensenada, Baja California, México.

INTRODUCTION: Rickettsiosis caused by Rickettsia rickettsii is capable of infecting vertebrates, including humans. The symptoms are high fever, headache, myalgia, nausea, vomiting, abdominal pain, and cough. Mortality can be up to 30% in untreated patients. AIMS: To prove the existence of rickettsiosis in Ensenada, Baja California, Mexico, because no human cases have been reported. MATERIAL AND METHODS: This observational, cross-sectional, descriptive study included 384 samples of humans in Ensenada, Baja California. Antibodies against R. rickettsii were measured with the kit R. rickettsii ELISA(®) Helica Biosystems, Inc., adapted for use in humans using human IgG conjugate antibodies. To determine the sensitivity and specificity, 32 human samples were submitted to IFA. Specific primers were used for the molecular diagnosis of R. rickettsii in dogs and ticks. RESULTS: The seroprevalence adjusted rickettsiosis in humans was 2.9% (95% CI: 0.8-5.3), seropositivity was not associated with sex, age, occupation, household, dogs, pet deworming program against ticks, the type of yard, and mobility of the dog between home and the street. CONCLUSIONS: With substantial agreement of k between ELISA and IFA, it follows that the results of seroprevalence of this work are reliable.