Prevalence of Ehrlichia canis, Anaplasma platys, Babesia canis vogeli, Hepatozoon canis, Bartonella vinsonii berkhoffii, and Rickettsia spp. in dogs from Grenada

Abstract

To identify the tick-borne pathogens in dogs from Grenada, we conducted a serologic survey for Ehrlichia canis in 2004 (104 dogs) and a comprehensive serologic and molecular survey for a variety of tick-borne pathogens in 2006 (73 dogs). In 2004 and 2006, 44 and 32 dogs (42.3% and 43.8%) were seropositive for E. canis, respectively. In 2006, several tick-borne pathogens were identified by serology and PCR. DNA of E. canis, Anaplasma platys, Babesia canis vogeli, Hepatozoon canis, and Bartonella sp. were identified in 18 (24.7%), 14 (19.2%), 5 (7%), 5 (7%), and 1 (1.4%) dogs, respectively. Six (8.2%) dogs were seropositive for Bartonella vinsonii subsp. berkhoffii. All dogs were seronegative and PCR-negative for Rickettsia spp. Coinfection with two or three pathogens was observed in eight dogs. Partial 16S rRNA E. canis and A. platys sequences were identical to sequences in GenBank. Partial 18S rRNA gene sequences from the Grenadian H. canis were identical to each other and had one possible mismatch (ambiguous base) from H. canis detected from Spain and Brazil. Grenadian B. c. vogeli sequences were identical to B. c. vogeli from Brazil and Japan. All of the detected pathogens are transmitted, or suspected to be transmitted, by Rhipicephalus sanguineus. Results of this study indicate that dogs from Grenada are infected with multiple tick-borne pathogens; therefore, tick-borne diseases should be included as differentials for dogs exhibiting thrombocytopenia, leukopenia, fever, or lethargy. One pathogen, E. canis, is also of potential public health significance.

Introduction

Tick-borne bacteria and parasites are significant pathogens of domestic dogs and potentially are of public health significance. At least five bacteria species in the genera Ehrlichia and Anaplasma (Ehrlichia canis, E. chaffeensis, E. ewingii, Anaplasma platys, and A. phagocytophilum) have been reported from domestic dogs. Canine monocytotropic ehrlichiosis in dogs is caused by either E. canis or E. chaffeensis. E. canis is a common pathogen of domestic dogs that has a worldwide distribution. Although not considered a zoonosis in the United States, human infections with E. canis, or a closely related organism, have been reported in Venezuela (Perez et al., 1996, Perez et al., 2006). The principal tick vector of E. canis is the brown dog tick, Rhipicephalus sanguineus (Lewis et al., 1977).

Canine granulocytotropic ehrlichiosis is caused by either E. ewingii or A. phagocytophilum. Anaplasma phagocytophilum has been found throughout the world in a number of vertebrate hosts (e.g., dogs, humans, deer, rodents) and is vectored by Ixodes species. E. ewingii is believed to share a similar natural history as E. chaffeensis with white-tailed deer as a potential reservoir and the lone star tick as a vector (Anziani et al., 1990, Yabsley et al., 2002). Recently, E. ewingii was reported from dogs in Cameroon where the lone star tick is not present; Rhipicephalus sanguineus was commonly detected on the dogs and was suggested as a potential vector (Ndip et al., 2005). Another canine pathogen, A. platys, infects platelets and causes canine infectious cyclic thrombocytopenia in numerous countries. Although R. sanguineus is a suspected vector, experimental studies have failed to prove vector competence (Simpson et al., 1991).

Babesiosis, caused by protozoan parasites in the genus Babesia, is a significant disease of domestic dogs. The two predominant species in dogs are B. gibsoni and B. canis which has been divided into three subspecies, B. c. canis, B. c. vogeli, and B. c. rossi. The three subspecies can be differentiated by sequence analysis of the rRNA gene and they differ in their natural history and virulence for dogs (Caccio et al., 2002, Criado-Fornelio et al., 2003, Inokuma et al., 2004, Matjila et al., 2004, Passos et al., 2005, Manzillo et al., 2006). B. c. rossi is transmitted by Haemaphysalis spp. and is considered the most pathogenic of the three subspecies. B. c. canis is transmitted by Dermacentor spp. and causes a variable clinical presentation while B. c. vogeli is transmitted by R. sanguineus and generally only causes a mild, often clinically inapparent infection.

Two species of Hepatozoon have been described from dogs (Ewing and Panciera, 2003). H. americanum, transmitted by A. maculatum, is only known from the United States and causes a severe disease (myositis and gait abnormalities) while H. canis, transmitted by R. sanguineus, is distributed throughout the Old World and usually causes a milder disease (mild anemia and lethargy) (Ewing and Panciera, 2003).Bartonella vinsonii subsp. berkhoffii can cause a wide range of clinical signs in dogs (Breitschwerdt et al., 2004). Infection in dogs is associated with tick infestations and is often detected in association with tick-transmitted organisms. R. sanguineus is a suspected vector (Pappalardo et al., 1997). Detection can be difficult as bacteremia is often low and pre-enrichment culture followed by PCR is necessary for sensitive detection (Duncan et al., 2007).

Recently, R. sanguineus has been implicated as a vector of Rickettsia rickettsii to dogs and humans in Arizona, USA (Demma et al., 2006, Nicholson et al., 2006). R. rickettsii can cause a severe disease in dogs, but those that survive develop antibodies and can be used as sentinels for the distribution of R. rickettsii (Demma et al., 2006, Breitschwerdt et al., 1987).

R. sanguineus is the only known tick to parasitize dogs on Grenada and is frequently detected on dogs. E. canis infection is commonly diagnosed at the Small Animal Veterinary Teaching Hospital (VTH) at St. George's University and is considered one of the most important infectious diseases of dogs on the island (McKibben, personal communication). In this current study, we used serologic and molecular testing to determine the prevalence of E. canis and other tick-borne pathogens suspected to be present in Grenada (e.g., those transmitted or suspected to be transmitted by R. sanguineus) in dogs. Because students at St. George's University frequently bring dogs from the United States, we surveyed for other tick-borne pathogens not transmitted by R. sanguineus to determine if other agents have been introduced.