Background: Nowadays,Ehrlichia canisreceives increasing attention because of its great morbidity and mortality in animals. Dogs in the subclinical and chronic phases can be asymptomatic, and serological tests show cross-reactivity and fail to differentiate between current and past infections. Moreover, there could be low parasitaemia, andE. canismight be found only in target organs, hence causing results to be negative by polymerase chain reaction (PCR) on blood samples.Methods: We evaluated by PCR the prevalence ofE. canisin blood, liver, spleen, lymph node and bone marrow samples of 59 recently euthanised dogs that had ticks but were clinically healthy.Results: In total, 52.55% of the blood PCRs forE. caniswere negative, yet 61.30% yielded positive results from tissue biopsies and were as follows: 63.15% from bone marrow; 52.63% from liver; 47.36% from spleen; and 15.78% from lymph node. In addition, 33% had infection in three tissues (spleen, liver and bone marrow).Conclusions: Our results show the prevalence ofE. canisfrom tissues of dogs that were negative by blood PCR.Ehrlichia canisDNA in tissue was 30% lower in dogs that tested negative in PCR of blood samples compared to those that were positive. However, it must be taken into account that some dogs with negative results were positive forE. canisin other tissues.

Tick-borne bacterial pathogens (TBBPs) show a worldwide distribution and represent a great impact on public health. The brown dog tick (Rhipicephalus sanguineus) is a vector of several pathogens that affect dogs and sometimes humans as well. In addition, TBBPs represent a diagnostic challenge and imply financial resources and medical treatment for long periods of time. In the present study, R. sanguineus s. l. was identified as the main tick species naturally parasitizing dogs that inhabit. Juárez City, Chihuahua, in the Paso del Norte region, Mexico–US Border, representing 99.8% of the cases. Additionally, an end-point PCR was performed to search for whether pathogens in R. sanguineus s. l. can transmit in DNA extracted from ticks and dog blood samples. This is the first molecular detection of Rickettsia rickettsi infecting domestic dogs in Mexico; however, other pathogens were also identified, such as Ehrlichia canis and Anaplasma platys in both ticks and dog blood samples, while Anaplasma phagocytophilum was identified only in dog blood samples. Moreover, co-detection in tick pools and co-infection in the analyzed dog blood samples could be found. Similarly, this research showed that dogs were found mostly parasitized by adult female ticks, increasing the possibility of transmission of E. canis.

This review provides an overview of the canine distemper virus (CDV), a highly infectious pathogen causing severe disease in domestic dogs and wildlife. It shares genetic similarities with the human measles virus (HMV) in humans and the rinderpest virus (RPV) in cattle. The origin of CDV likely involves a mutation from human measles strains, possibly in the New World, with subsequent transmission to dogs. CDV has been globally observed, with an increasing incidence in various animal populations. Genomic mutations, especially in the H protein, contribute to its ability to infect different hosts. Diagnosis by molecular techniques like RT-qPCR offers rapid and sensitive detection when compared with serological tests. Genomic sequencing is vital for understanding CDV evolution and designing effective control strategies. Overall, CDV poses a significant threat, and genomic sequencing enhances our ability to manage and prevent its spread. Here, the epidemiology of CDV principally in Mexico is reviewed.

Currently, ticks are second in transmission of pathological agents to humans, and in the veterinary field are ranked first. Thus, pathogens that might be in contact with human and animal populations, especially farm animals such as horses, Equus caballus (Linnaeus), should be identified. Two species of soft ticks in the Argasidae family, Otobius megnini (Duges) and Ornithodoros turicata (Duges), and one hard tick of the Ixodidae family, Rhipicephalus sanguineus (Latreille) were identified. DNA of pathogens Theileria equi (Laveran), Babesia caballi (Nuttall and Strickland), and Anaplasma phagocytophilum (Foggie) that have been reported in species of hard ticks but not soft ticks were identified. Overall, 144 blood samples from horses at Ciudad Juárez, Chihuahua, Mexico, were processed for DNA extraction, and analyzed by end-point or nested PCR to identify pathogens. The prevalence of T. equi was 6.9% (10/144) and 5.9% (3/51) in blood samples and soft tick samples, respectively; the prevalence of B. caballi was 2.8% (4/144) in blood samples and 5.9% (3/51) in soft ticks. There was one case of coinfection with both pathogens, and one blood sample tested positive for A. phagocytophilum, indicating a prevalence of 0.8% (1/124). The results suggested that soft ticks evaluated are potential vectors and might play a role in transmission of the pathogens.

Biting midges (Culicoides) are vectors of many pathogens of medical and veterinary importance, but their viromes are poorly characterized compared to certain other hematophagous arthropods, e.g., mosquitoes and ticks. The goal of this study was to use metagenomics to identify viruses in Culicoides from Mexico. A total of 457 adult midges were collected in Chihuahua, northern Mexico, in 2020 and 2021, and all were identified as female Culicoides reevesi. The midges were sorted into five pools and homogenized. An aliquot of each homogenate was subjected to polyethylene glycol precipitation to enrich for virions, then total RNA was extracted and analyzed by unbiased high-throughput sequencing. We identified six novel viruses that are characteristic of viruses from five families (Nodaviridae, Partitiviridae, Solemoviridae, Tombusviridae, and Totiviridae) and one novel virus that is too divergent from all classified viruses to be assigned to an established family. The newly discovered viruses are phylogenetically distinct from their closest known relatives, and their minimal infection rates in female C. reevesi range from 0.22 to 1.09. No previously known viruses were detected, presumably because viral metagenomics had never before been used to study Culicoides from the Western Hemisphere. To conclude, we discovered multiple novel viruses in C. reevesi from Mexico, expanding our knowledge of arthropod viral diversity and evolution.