Population genetics of the Ixodes affinis (Ixodida: Ixodidae) complex in America: new findings and a host-parasite review.

Ticks are hematophagous ectoparasites associated with a wide range of vertebrate hosts. Within this group, the Ixodidae family stands out, in which the Ixodes genus contains at least 245 species worldwide, from which 55 species are present in the Neotropical region. Ixodes affinis, a tick described in 1899, has a wide distribution from the Southern Cone of America to the United States. However, since its description, morphological variability has been reported among its populations. Furthermore, attempts have been made to clarify its status as a species complex using mitochondrial markers, but mainly in restricted populations of South and Central America. Thus, information related to populations of the transition region between the Neotropical and Nearctic zones is lacking. For these reasons, the objectives of the study were to evaluate the genetic diversity and structure of I. affinis across the Americas and to compile all the published records of I. affinis in America, to elucidate the host-parasite relationships and to identify their geographical distribution. For this, a phylogeny, and AMOVA analyses were performed to assess the genetic structure of samples obtained by field work in South Carolina, USA and Yucatán, Mexico. A total of 86 sequences were retrieved from a fragment of the 16S region. Phylogeny and genetic structure analysis showed four groups that were geographically and genetically related with high branch support and Fst values, all of them statistically significant. The results obtained support the hypothesis that I. affinis it corresponds to a complex of four species, which must be validated through future morphological comparisons.

First morphological and molecular report of Lagochilascaris minor (Nematoda, Ascarididae) in a domestic cat from Veracruz, Mexico.

The clinical presentation and the morphological and molecular findings of Lagochilascaris minor in a domestic cat from Veracruz, Mexico are described. In the physical examination of the cat, a fistula with purulent exudate was observed in the ventral middle and left lateral region of the neck, with the presence of nematodes inside. Thirty-two worms were recovered from the lesion, which were identified based on their morphological characteristics as Lagochilascaris spp. To determine the species of the nematode, DNA was extracted from the worms and a fragment of the cytochrome C oxidase subunit 1 was amplified. The product obtained was 100% similar with L. minor from Costa Rica. This is the first morphological and molecular report of L. minor parasitizing a domestic cat from Veracruz, Mexico, and emphasizes the circulation of this zoonotic parasite in the country.

Monitoring the resistance of Rhipicephalus microplus to amitraz, flumethrin, coumaphos, and ivermectin on cattle farms in Mexico.

The prevalence, resistance ratios and factor associated with Rhipicephalu microplus populations resistant to amitraz, flumethrin, coumaphos, and ivermectina (IVM) in Mexico were studied. Field tick populations were collected from 54 farms in 15 different states of Mexico. The dose-response bioassays were carried out using the larval immersion test (amitraz and IVM) and the modified larval packet test (flumethrin and coumaphos) against R. microplus. Mortality data were subjected to probit analysis to calculate lethal concentrations at 50%. A logistic regression model was used to evaluate the relation between resistance and possible associated factors. The phenotype was defined as high resistant (HR), low resistant (LR) or susceptible (S). The overall prevalence of cattle farms with R. microplus resistant to coumaphos, amitraz, flumethrin and IVM were 25.9, 46.2, 31.5 and 68.5%, respectively. For coumaphos, 74.1, 22.2, and 3.7% were classified as S, LR, and HR, respectively, whereas, for amitraz, 53.7, 24.1, and 22.2% of phenotypes were S, LR, and HR, respectively, for flumethrin 68.5, 14.8, and 16.7% were S, LR and HR respectively, and for IVM, 31.5, 46.3, and 22.2% were S, LR, and HR, respectively. We identified that cattle farms without acaricide rotation program (OR: 7.66, CL95%: 1.70-34.47, P: 0.008) had a higher probability of developing R. microplus resistant to amitraz. We concluded that amitraz and IVM resistance in R. microplus is frequent, but mainly at a low level in cattle farms of Mexico. Cattle farms without acaricide rotation program had higher probability of developing R. microplus resistant to amitraz.

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.

Ehrlichia canis in dogs of Mexico: Prevalence, incidence, co-infection and factors associated.

Rickettsial infections in dogs of Mexico were investigated. A total of 246 dogs were blood sampled and initially screened to detect Ehrlichia canis, E. chaffeensis, E. ewingii, Anaplasma phagocytophilum and Rickettsia rickettsii by a quantitative real-time PCR (qPCR) assay. Sixty-five dogs were monitored and sampled twice 7-8 months apart. Using the qPCR, 72 positive dogs to E. canis were detected (prevalence of 29.26%). These dogs were also tested by nested PCR to detect the same pathogens. None of the studied dogs were positive to E. chaffeensis, E. ewingii, R. rickettsii nor A. phagocytophilum by both PCR assays. The cumulative incidence of E. canis infection was 38.46%. Sequencing analysis of the nested PCR products revealed 100% and 98.1% identity of E. canis and R. parkeri, respectively. We found a dog co-infected with E. canis and R. parkeri.

Ticks infesting dogs in rural communities of Yucatan, Mexico and molecular diagnosis of rickettsial infection.

Rickettsial infection in dog-associated ticks in three rural communities of Yucatan, Mexico was investigated using qPCR and nested PCR assays. A total of 319 dogs were studied and ticks samples were collected. A total of 170 dogs were infested with ticks (frequency of 53.4%). Overall, 1,380 ticks representing seven species were collected: Amblyomma mixtum, A. ovale, A. parvum, A. cf. oblongoguttatum, Ixodes affinis, Rhipicephalus microplus, and R. sanguineus sensu lato. The most abundant species was R. sanguineus s.l. with a mean intensity of 7.4 ticks/host. Dogs in the communities of Chan San Antonio and Yaxcheku were 2.84 and 2.41 times more likely to be infected with R. sanguineus compared with Sucopo (p < 0.05). Adult pools of A. mixtum, A. parvum, I. affinis, R. microplus, and A. c.f. oblongoguttatum were negative to E. chaffeensis, E. ewingii, A. phagocytophilum, and R. rickettsii. However, pools of R. sanguineus s.l. adults and A. ovale adults, as well as nymphs of Amblyomma spp. were positive to E. canis. Sequencing analysis of the nested PCR products amplifying the 16S rRNA gene fragment of E. canis confirmed the results and revealed 100% identity with sequences of E. canis. This is the first report worldwide of E. canis infection in A. ovale by PCR. This finding does not necessarily indicate that A. ovale is a competent vector of E. canis because pathogen transmission of this specific tick to a naïve dog remains to be documented. This study documented that different tick species parasitize dogs in Yucatan, Mexico, where R. sanguineus s.l., A. ovale, and nymphs of Amblyomma spp. were shown to be infected with E. canis. These findings highlight the need for control strategies against tick infestations in dogs to prevent the risk of tick-borne disease transmission among companion animal and probably human populations.