doi:10.5455/vetworld.2013.42-44 Canine leptospirosis – a seroprevalence study from Kerala, India

Aim: To study the seroprevalence of leptospirosis in dogs in Kerala and to identify the most prevalent serovar. 
 
Materials and Methods: A total of 205 sera collected from dogs were screened for the presence of antibodies against leptospirosis by Microscopic Agglutination Test (MAT). 
 
Results: A seroprevalence rate of 71.12 per cent was observed. Leptospira interrogans serovar Autumnalis was found to be the most prevalent serovar followed by Australis, Pomona, Canicola, Pyrogenes, Icterohaemorrhagiae, Javanica and Patoc. 
 
Conclusions: The results revealed the high prevalence of anti leptospiral antibodies in dogs in Kerala. The emergence of serovars other than the vaccinal serovars necessitates the incorporation of these in the vaccines because the immunity against leptospirosis is serovar specific. 
 
Key words: canine leptospirosis, MAT, seroprevalence


Introduction
All the samples were subjected to Microscopic Agglutination Test (MAT).A battery of eight pathogenic Leptospirosis, a spirochaetal zoonosis, has emerged serovars viz., Leptospira interrogans serovar Australis, as a serious global veterinary and public health Autumnalis, Canicola, Grippotyphosa, Icterohaemoproblem rrhagiae, Javanica, Pomona and Pyrogenes and non Many places in South India, pathogenic Patoc I strain of L. biflexa serovar Patoc including Kerala, are known to be endemic for procured from the National Leptospira Reference leptospirosis [2].The pathogenic leptospires are centre, Regional Medical Research Centre, Port Blair, divided into more than 250 different serovars and the Andaman and Nicobar Islands were used as antigens in most common serovars affecting dogs include the test.These cultures were maintained in Leptospira Canicola, Icterohaemorrhagiae, Pomona, Bratislava, liquid culture medium (Difco) with bovine serum Grippotyphosa and Australis [3].Despite routine albumin supplement.The test was carried out in a 96 vaccinations, there are increasing reports of canine well U-bottom microtitre plates.Test sera were first leptospirosis in Kerala.The commercial vaccines are diluted to 1:50 and then serially diluted two fold in becoming less effective because the immunity is phosphate buffered saline, to obtain dilutions of 1: 100 serovar specific and new serovars are emerging [4].
to 1: 25600.To 30 µl each of the serum dilution, 30 µl of Therefore for successful immunization, it is essential to six day old live antigen was added.Appropriate antigen identify the most predominant serovar in the specific controls were set with 30 µl PBS and 30 µl of antigen o region.Hence, the present study was undertaken to and the plates were incubated at 37 C for two hours.identify the prevalence of various serovars involved in After incubation, the result was read by examining a canine leptospirosis in three regions of Kerala viz., drop of serum-antigen mixture from each well under Thrissur, Palakkad and Kozhikode.dark field microscope.The antibody titre was the highest dilution of serum showing agglutination of 50

Materials and Methods
per cent or more leptospiral organisms.Reciprocal A total of 205 canine serum samples were collected agglutination titres of greater than or equal to 100 were from three regions of Kerala viz., Thrissur, Kozhikode considered as positive reactions [5].The serovar and Palakkad during a period from March, 2011 to reacting at the highest titre was considered to be the February, 2012.The samples included those collected infecting serovar.Sera samples showing same from 35 healthy vaccinated animals and 30 healthy agglutination titres to more than one serovar were unvaccinated animals.The rest of the samples were considered as mixed equals.taken from cases suspected for acute leptospirosis.

Results
Paired samples were collected from eight dogs which were diagnosed as positive for acute leptospirosis.
One hundred and forty six samples (71.12 per .The disease has gained much importance as it is often undiagnosed [1].cent) including the 30 healthy vaccinated animals were According to various studies conducted in found to be positive by MAT.The sera from 35 healthy southern states of India, Australis was reported to be unvaccinated animals were found to be negative.In the emerging serovar [3] [10].A seroprevalence study vaccinated healthy animals, agglutination was conducted in Kerala in 2004 revealed Pomona as the observed against serovars Canicola and Icterohaemo-most prevalent serovar affecting dogs [11].However, rrhagiae which are included in the common in the recent studies, serovars Australis and Autumnalis commercial vaccine.Among the eight paired serum were found to be more predominant here [12], [13], samples collected, except one all showed a four fold [14].Variation could be noticed over years in the increase in MAT titre.
prevalence of leptospirosis in animals.Most of the The MAT titres varied from 1: 100 to 1: 6400.The above studies in Kerala were restricted to Thrissur most predominant serovar was found to be Autumnalis district only.Hence, a detailed seroprevalence study is followed by Australis, Pomona, Grippotyphosa, necessary covering the entire state.Canicola, Pyrogenes, Icterohaemorrhagiae, Javanica, and Patoc (Table -  RA carried out the study and prepared the article.MM and SJ participated in scientific discussion, SVK and GA assisted in conducting MAT.All authors read and approved the final manuscript.Microscopic Agglutination test is considered as epidemiological data in the form of presumptive the study.We also thank Dean, College of Veterinary serovars.A titre of 1:100 and above is considered as and Animal Sciences, Mannuthy for giving the positive in MAT [5].
necessary facilities to carry out the work and National However, in an endemic region, where vaccination is routinely Leptospira Reference centre, Regional Medical practiced, this titre has to be increased to confirm the Research Centre, Port Blair, Andaman and Nicobar presence of acute infection [6] as there were antibodies Islands for providing the reference serovars used in the in healthy vaccinated animals.
study.The study reveals the emergence of Autumnalis as

Competing interests
the most predominant serovar in the region.Similar results were obtained in a survey of canine leptospirosis Authors declare that they have no competing interests.on the island of Barbados, where Autumnalis was found to be the most common reactor, followed by between the reservoirs of infection in the environment 5. Office Internationale des Epizootis (2004) Leptospirosis.In and the human beings.

Discussion
In the present study, 146 (71.12 per cent) sera had titre above this.
Javanica and Pyrogenes and Canicola, Though the current vaccines against leptospirosis Icterohaemorrhagiae and Pomona.The area wise in Kerala contains the serovars Icterohaemorrhagiae prevalence of different serovars was not studied.andCanicola, the present study reveals the need of Conclusionsrrhagiae,

Table - 1
. Seroprevalence of canine leptospirosis incorporating the serovar Autumnalis as it was found to