A survey of tick-borne bacteria and protozoa in naturally exposed dogs from Israel
Introduction
Tick-borne pathogens are a major cause of disease in many regions of the world including Israel. Lyme disease, granulocytic ehrlichiosis and Rocky Mountain spotted fever are diseases of comparative medical importance since both dogs and humans contract illness through tick infestation. Other tick-borne infectious organisms such as Ehrlichia canis, Babesia canis and Babesia gibsoni are pathogenic to canids but not to humans. Dogs which spend much of their time outdoors and often are allowed to roam freely are exposed extensively to ticks during the tick season which varies in length depending on climatic conditions. Ticks can survive for long periods of time off a vertebrate host, and may then find a new host. Many tick species that infest dogs may feed on other hosts including domestic livestock, wildlife carnivores, rodents, and man. Acaricidal treatment of dogs by their owners is often ineffective or completely lacking.
Tick-borne pathogens may cause an acute or chronic disease in susceptible hosts. Other hosts recover spontaneously by elimination of the infective organisms, or may develop a carrier state. Exposure to a pathogen, regardless of whether it results in elimination of the causative agent, or in a state of subclinical infection, produces in most instances an antibody response that can be measured in the animal's serum.
This report describes antibody prevalence to six tick-borne pathogens in dogs from Israel, in which a tick-borne disease was suspected based on clinical history, physical examination and blood tests results. E. canis is a rickettsia that is known to cause a severe disease in dogs (Troy and Dru Forrester, 1990). Canine ehrlichiosis was first described in dogs from Israel in 1972 (Klopfer and Nobel, 1972). Recently, an Israeli strain of E. canis (Keysari et al., 1995) and the prevalence of antibodies against this pathogen in dogs from Israel have been reported (Baneth et al., 1996). B. canis and B. gibsoni are two piroplasm parasites of the red blood cells (RBC) of dogs (Breitschwerdt, 1990). Although B. canis is recognized as a pathogen of dogs in Israel, B. gibsoni has not been reported from this country. B. gibsoni infection has been described in dogs from many regions including: Egypt, the Far East (Purnell, 1981), southern Africa (Matthewman et al., 1993), and North America (Conrad et al., 1991). Rickettsia conorii, the causative agent of Mediterranean spotted fever in humans, is transmitted by the tick Rhipicephalus sangineus and antibody reactivity against this spotted-fever group rickettsial organism has been reported also in dogs (Keysari et al., 1988). Unlike Rickettsia rickettsii which causes Rocky Mountain spotted fever in both dogs and humans, it is not known whether R. conorii can cause disease in dogs. Two strains of R. conorii, one from Morocco and another from Israel (Israel 2) were used in this study. Borrelia burgdorferi is the causative agent of Lyme disease in humans and dogs. Antibody reactivity against a Borrelia sp. in one dog in Israel has been reported previously (Harrus and Bark, 1994) but little evidence concerning the identity of the actual Borrelia was presented and it is not clear whether the reported dog was infected by B. burgdorferi, a different Borrelia species or a serologically cross-reacting organism. Bartonella vinsonii berkhoffii is a gram-negative bacteria that has been isolated from the blood of dogs in North America and is associated with endocarditis (Breitschwerdt et al., 1995). Seroepidemiologic evidence of the transmission of B. vinsonii berkhoffii by ticks has been reported (Pappalardo et al., 1997).
In addition to describing the association between clinical findings in dogs suspected of tick-borne disease and seroreactivity to selected tick-borne pathogens, our aims were to determine the seroprevalence of tick-transmitted pathogens among dogs suspected of tick-borne infection in Israel, and to provide serologic data suggesting the presence of tick-transmitted pathogens that have not previously been described in Israel.
Section snippets
Dogs sampled
Paired, acute and convalescent, (n=20) or single (n=20) serum samples were obtained from dogs suspected of tick-borne illness that were admitted for examination at the Hebrew University Veterinary Teaching Hospital in Israel during the spring and summer of 1994. Initial examination of the dogs consisted of a comprehensive physical examination which included palpation of the prescapular and popliteal lymph nodes, abdominal palpation for an observation of the spleen size, and an inspection of the
Results
Of the 40 dogs in this study, 45% (18/40) were males and 55% (22/40) females. Thirty percent of the dogs were of mixed breeding and the remaining 70% were of various breeds with no particular breed represented by more than six dogs. The age distribution, clinical and hematological abnormalities are presented in Table 1.
Two dogs (in youngest age group) reacted with no antigens (Table 2) and no dog reacted with all of the antigens. Seventy three percent (29/40) reacted with three or more antigens
Discussion
Our findings demonstrate that most of the dogs in this study had antibody titers to several tick-borne pathogens and were therefore presumably exposed to a variety of vector-transmitted organisms. The demonstration of antibodies reactive with a certain antigen in the serum of a dog may be due to a past exposure which resolved, a current subclinical infection, or recent `active' infection. As clinical signs of several tick-borne diseases of dogs, including ehrlichiosis, babesiosis and Rocky
Acknowledgements
We thank Robin Gager, Dr. Michael Levy and Dr. Jay F. Levine from the North Carolina State University for their technical assistance. We also thank Dr. Tom Schwan, National Institutes of Health, for donating the anti-p39 monoclonal antibodies and Dr. David H. Walker from the University of Texas, Medical Branch, Galveston, TX for providing the R. conorii strains used in this study.
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