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

Authors: OJEDA-CHI, MELINA - Universidad Nacional Autonoma De Mexico; RODRIGUEZ-VIVAS, ROGER IVAN - Universidad Nacional Autonoma De Mexico; ESTEVE-GASENT, MARIA - Texas A&M University; Perez De Leon, Adalberto - Beto; MODARELLI, JOSEPH - Texas A&M University; VILLEGAS-PEREZ, SANDRA - Universidad Nacional Autonoma De Mexico

Submitted to: Transboundary and Emerging Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2018
Publication Date: 8/13/2018
Citation: Ojeda-Chi, M.M., Rodriguez-Vivas, R.U., Esteve-Gasent, M.D., Perez De Leon, A.A., Modarelli, J.J., Villegas-Perez, S.L. 2018. Ticks infesting dogs in rural communities of Yucatan, Mexico and molecular diagnosis of rickettsial infection. Transboundary and Emerging Diseases. 2018:1-9.

Interpretive Summary: Rickettsia are bacteria that can be transmitted by ticks and cause disease in domestic animals and humans. Determining the frequency of tick infestation in animals and the rate of rickettsial infection in those ticks helps assess the risk for tick-borne disease in the human or animal population sampled. Out of 319 dogs surveyed in Yucatan, Mexico, 170 dogs (53.4%) were infested with ticks. There were 1,380 ticks collected in total representing 7 different species. The brown dog tick, Rhipicephalus sanguineus, was the most abundant species collected in this survey where an average of 7.4 brown dog ticks were found per dog. Modern molecular techniques were used to identify diverse bacterial species found in all of the ticks that were collected. Another disease-causing bacteria called Ehrlichia canis was identified in adult brown dog ticks and in Amblyomma ovale adults, as well as in the immature stages of Amblyomma ticks. This is the first report worldwide of E. canis infection in A. ovale. Since E. canis was found in this tick species, it could potentially be passed on to animals, like pet dogs, and cause disease. These findings highlight the need for proper control of tick infestations in companion animals so the ticks don't move to bite humans, which increases the risk of exposure to tick-borne diseases.

Technical Abstract: 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.