Coinfection of Leptospira and T. Gondii among Stray Dogs

Leptospirosis and toxoplasmosis are zoonotic diseases with global importance. Asymptomatic animals harboring these pathogens may act as carriers to other animals including humans. The objective of this study was to investigate the seroprevalence of Leptospira and Toxoplasma infections in stray dogs in Bangkok. A total of 230 stray dogs from monasteries in a Bangkok district were examined for specific antibodies to T. gondii and Leptospira. The seroprevalence of T. gondii was determined by a modified latex agglutination test (cut off 1≥64). A microscopic agglutination test was performed to detect antibodies to Leptospira (cut off, 1:100). The seroprevalences of T. gondii and Leptospira were 10.9% (25/ 230) and 83.5% (192/230), respectively. Leptospira serovar bataviae was the most predominant (20.3%) serovar. Co-infection with Leptospira and Toxoplasma was found in 22 dogs (9.6%). The prevalence of Toxoplasma in females was significantly higher than in males (p<0.05), but no significant differences was observed for Leptospira. The high seroprevalence of these two diseases in dogs is of public health concern because close contact between dogs and humans may provide a link between a reservoir in the environment and susceptible humans. ferent leptospiral serovars in a human population depends on the reservoir animals, as well as local environmental conditions, occupation, agronomical, and agricultural practices. Southeast Asia is endemic for leptospirosis. It has been reported that dogs play an important role in the transmission of leptospirosis to humans in India (Venkataraman and Nedunchelliyan, 1992). In Thailand, stray dogs have become of public health concern since the numbers increase annually, especially in Bangkok metropolitan areas (Jittapalapong et al, 2003). This increases the risk for spreading of leptospirosis to humans since the infection results from INTRODUCTION Leptospirosis and toxoplasmosis are important zoonoses affecting both animals and human beings. The incidence of human leptospirosis is higher in the tropics than in temperate regions but transmission occurs in both industrialized and developing countries (WHO, 2003). The prevalence of difSOUTHEAST ASIAN J TROP MED PUBLIC HEALTH 248 Vol 40 No. 2 March 2009 exposure to urine of carrier mammals, either directly or via contaminated soil or water. Toxoplasma gondii is an obligate, intracellular, protozoan parasite with a worldwide distribution. Infection with T. gondii is wide spread in many species of animals, including humans, and it is estimated to infect 30% of the human population worldwide (Aspinall et al, 2002). Although the infection usually does not cause a significant problem for healthy individuals, it can be life-threatening for congenitally-infected and immunosuppressed individuals (Chintana et al, 1998). T. gondii infects human beings either by direct contact with infected animals, ingesting oocysts or by eating raw, undercooked meat or unpasteurised milk containing infective stages of the parasite (Riemann et al, 1975; Sacks et al, 1982). Dogs play a role in transmission of T.gondii to humans without having clinical signs of Toxoplasma infection similar to cats (Lindsay et al, 1997). Dogs are also capable of mechanically shedding oocysts, contaminating the environment (Dubay, 1996). These facts indicate the importance to public health of investigating the prevalence of both Leptospira and Toxoplasma infections in stray dogs. The objective of this study was to determine the seroprevalence of Leptospira and Toxoplasma infections in stray dogs in Bangkok, Thailand. MATERIALS AND METHODS Study areas and animals The dog samples were collected in a district located in the center of Bangkok. More than 20 Buddhist monasteries exist in this area and many stray dogs inhabit in this area. A total of 230 stray dogs were obtained randomly from monasteries in this district. One hundred fifteen male and 115 female dogs were collected. Dogs were examined for sex, general condition and status of ectoparasites. Blood samples were collected and the sera were separated by centrifugation at 500g for 30 minutes at the Department of Parasitology, Faculty of Veterinary Medicine, Kasetsart University and stored at -20oC until analysis. Detection of antibodies to Leptospira spp Serum samples were tested for the infection due to leptospirosis using the following 21 serovars as antigens: L. bratislava, L. autumnalis, L. ballum, L. bataviae, L. canicola, L. cellidoni, L. cynopteri, L. djasiman, L. grippotyphosa, L. hebdomadis, L. icterohaemorrhagiae, L. javanica, L. louisiana, L. manhao, L. pomona, L. ranarum, L. sarmin, L. sejroe, L. shermani, L. tarassovi, and L. patoc. A microscopic agglutination test was performed as previously described (Cole et al, 1973). In brief, the dog sera were inactivated by heating at 56oC for 30 minutes and diluted by two fold dilution beginning with a 1:25 solution on a U-shaped micro plate. A volume of 50 μl of each dilution was made for each serum sample with an approximate concentration of 108Leptospira organisms per sample and incubated at 37oC for 2-4 hours. Only antigens and an equal volume of PBS were added to the plate as negative antigen controls. Rabbit serum positive for homologous strain antigens were used as a positive control. Fifty percent agglutination at a 1:100 dilution was considered to be positive (WHO, 2003). Detection of antibodies to Toxoplasma gondii Antibody to T. gondii was analyzed using a latex agglutination test kit (TOXOCHECK-MT ‘Eiken’ Chemical, Tokyo, Japan). Positive and negative controls were used for each test. The procedure was carried out as previously described (Jittapalapong et al, 2005). The cut-off titer for a positive test was 1:64, as set by the manufacturer of the COINFECTION OF LEPTOSPIRA AND T. GONDII AMONG STRAY DOGS Vol 40 No. 2 March 2009 249 Seropositive Overall Number % Number % Number % Leptospira only 183 79.6 101 87.8 82 71.3 Toxoplasma only 25 10.9 7 6.1 18 15.7 Co-infection 22 9.6 7 6.1 15 13 Leptospira overall 205 89.1 108 93.9 97 84.3 Toxoplasma overall 47 20.4 14 12.2 33 28.7 Total 230 115 115 Table 1 Results of Leptospira and Toxoplasma in stray dogs in Bangkok, Thailand.