Leptospirosis in recent years has assumed considerable significance as the disease is increasingly being involved in cases of abortions, repeat breeding and other reproductive problems in livestock resulting in huge economic losses. In man, the disease is associated with a mild fever to severe jaundice and death as a result of multiorgan failure. Preliminary reports on occurrence of leptospirosis in cattle in India were documented by Adinarayanan et al. (1960). Subsequently, the prevalence of the disease in animals from various parts of the country has been reported by Rajasekhar & Nanjiah (1971), Srivastava et al (1983, 1990), Verma et al. (2001), Piramanayagan et al. (2002), Sivaseelan et al.(2003). The disease is caused by a spirochete belonging to the species Leptospira interrogans known to be comprised of more than 280 serovars, however, only 9-10 serovars are commonly responsible for causation of the disease. Because of the severity of the disease in animals and the economic losses, it is imperative that continuous efforts are made to screen the affected population for finding out the prevalence of the disease in livestock. In the present communication, seroprevalence of leptospirosis in animals of various parts of the country during a ten year period (1990-2000) is being reported.

A total of 4992 sera from various animals were screened for leptospiral antibodies by MAT, and their statewise and species wise distribution is given in Table 1. Most of the sera from cattle, buffalo, sheep and goats were from cases of reproductive disorders viz. abortion, repeat breeding, sterility etc. All these sera were earlier found to be negative for brucellosis. Swine and canine sera were from cases of fever, jaundice or nephritis. Equine sera were from cases of pyrexia with corneal opacity in a few cases. Besides these, a total of 532 human sera received from medical colleges or health departments of various states were also tested by MAT.

The sera were tested for antibodies using microscopic agglutination test (MAT) using a panel of Leptospira serovars namely Icterohaemorrhagiae, Australis, Autumnalis, Sejroe, Hardjo, Tarassovi, Grippotyphosa, Canicola, Pyrogenes, Ballum, Pomona, Hebdomadis, Bataviae, Javanica, Copenhageni, Patoc, Saopaulo and Andamana.

The test was performed as described by Faine (1982). Sera showing a titer of 1:100 or above were considered to be from animals either previously exposed to the Leptospira organisms or currently suffering from the disease.

The prevalence data on total animal samples from various states is summarized in Table 1. Maximum number tested for leptospirosis belonged to cattle (2601) followed by equine (756), sheep (551), buffalo (443), goats (271), dogs (204) and swine (166) with seropositivity for leptospirosis was observed in 15.8%, 9.9%, 15.2%, 2.7%, 14.3%, 19.1%, 89.0%, respectively. Majority of the infected cattle were from A.P. and Gujarat with a history of abortions, repeat breeding etc. Most of the sera from Gujarat belonged to animals from Navsari distt where an abortion storm, a characteristic of leptospirosis outbreak, among cattle was reported in the year 1997 (Srivastava, 1998). Thus, the present serological findings correlated with the clinical manifestations and indicated endemicity of leptospirosis in these states. Majority of buffalo sera were received from AP, however, the seropositivity in these animals was much less than observed in cattle. The reason could be that probably these animals were from other areas of AP. Majority of the infected sheep and goat belonged to AP, UP and HP. In AP the seropositivity of leptospirosis was higher in sheep than other states. Screening of goat samples from Mathura and Agra of UP revealed a high seroprevalence of leptospirosis in goats reared in these areas. Leptospirosis has been reported to be widely prevalent in southern states including AP. (Mrunalini and Ramasastry, 2000; Piramanayagan et al., 2002; Seevaseelam et al., 2003). The present study has further confirmed these observations. The equine sera mostly belonged to army horses stationed at various studs chiefly at Udhampur and Saharanpur. An overall seropositivity percentage of 9.9% was recorded. In Karnataka, the equine sera were from mares belonging to private equine breeding farms and many of these animals had a history of corneal opacity, a characteristic clinical sequel of leptospirosis in horses. The highest seropositivity for leptospirosis was recorded in case of dogs suggesting them to be a source of infection to the owners since recovered or convalescent dogs shed a large number of organisms in urine for a long period as compared to other animal species. Such shedders also serve as a source of infection to other susceptible animals.

Efforts were also made to collect sera from wild animals, since in many countries wild animals have been found to be the source of infection to domestic species. In the present study a total of 32 sera from cheetal and 16 from deer from Delhi zoo were screened and 2 cheetal sera were found positive to serovar Patoc. Moreover, 6 out of 32 sera from sambher, belonging to Lucknow zoo also tested positive, three of them to serovar Pomona, 2 to Pyrogenes and 1 to Javanica. Out of 21 elephants and 11 tigers belonging to zoos in UP, AP or Gujarat, only 4 and 2 animals, respectively, were found positive. These sera were positive to Ballum (2) or Pyrogenes (4). In India, seroprevalence of leptospirosis among wild animals has been reported earlier (Adinarayana & Chackojames, 1980; Upadhyay et al, 1979).

Distribution of various Leptospira serovars responsible for seroconversion in animals as a result of exposure or infection are given in Table 2. Common Leptospira serovars detected were Icterohaemorrhagiae, Patoc, Australis, Autumnalis, Grippotyphosa, Pyrogenes, Ballum, Hardjo, Pomona and Canicola. Other serovars found responsible were Bataviae, Javanica, Hebdomadis, Sejroe, Copenhageni and Andamana. Most of these serovars have been reported earlier in animals in various regions of the country. No animal species specificity was observed as regards the distribution of Leptospira serovars is concerned. There were many samples which reacted with more than one serovar suggesting that several serovars simultaneously could be responsible for the infection. Information on the distribution of Leptospira serovars in animals is essential for selecting serovars for preparation of vaccines.

During the present investigation, serum samples (532) from farmers, animal owners, slaughter house workers, sewage workers etc. with or without history of fever or jaundice were received from medical colleges located in Mumbai, Pune, Chandigarh or Gwalior and subjected to MAT and of these 78 (14.6%) had antibody titres suggestive of leptospirosis. Majority of the positive cases (265) were from Mumbai or Pune medical colleges with 43 (16.2%) of these showing positivity to various serovars. Of the remaining human sera from Chandigarh (12), Bareilly (80), Delhi (90), Gwalior (48) and Nellore (37), none from Chandigarh or Bareilly turned out positive for the leptospirosis, whereas 5 from Nellore showed positivity to serovar Andamana and one to Hardjo. Interestingly, a high percentage of sera (21.10%) from abbatoir workers or goat owners who had brought their animals for slaughter to Delhi were found positive for serovars Patoc (7), Pyro (3), Pomona (3) Autamnalis (4) and Icterohaemorrhagiae (2), probably due to close contact with animals. Among the positive human sera (10) from Gwalior, 9 were positive to Patoc and 1 to Canicola. Most of these serovars have also been detected in animals suggesting the transmission of infection from animals to man. The occurrence of leptospirosis in man in various states of the country is well documented (Sehgal et al., 2000; Kalimuthuswamy et al., 2002).

The present study highlighted that leptospirosis continue to be an important health problem in all species of animals as well as in human beings with a variety of clinical manifestations. It is concluded that epidemiological studies on this disease should continue with a view to monitor the disease trend as well as to evolve control measures.

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