|Year : 2014 | Volume
| Issue : 1 | Page : 64-67
Prevalence of leptospirosis among dogs and rodents and their possible role in human leptospirosis from Mumbai, India
D Patil, R Dahake, S Roy, S Mukherjee, A Chowdhary, R Deshmukh
Department of Virology, Haffkine Institute, Mumbai, Maharashtra, India
|Date of Submission||16-Jul-2013|
|Date of Acceptance||13-Sep-2013|
|Date of Web Publication||4-Jan-2014|
Department of Virology, Haffkine Institute, Mumbai, Maharashtra
Source of Support: The project is solely funded by Haffkine Institute,
Parel, Mumbai, India,, Conflict of Interest: None
A total of 100 blood and 18 urine samples of rodents and suspected dogs were collected from Mumbai, India during 2006-2008. In order to determine the role of animals in transmission of the disease to humans, all the samples were screened retrospectively by real-time polymerase chain reaction for leptospiral DNA and antibodies were detected using microscopic agglutination test. Leptopsiral DNA was detected from two blood and five urine samples from rodents. Of a total of 71 rodent and dog samples investigated for anti-Leptospira antibodies, 14 (19.7%) were positive. Pyrogenes was the predominant serovar found in 100.0% (7/7) and 85.7% (6/7) from suspected canine cases and rodents, respectively; followed by Icterohemorrhagiae, which was found in one rodent sample 14.28% (1/7). The study proves that there is high prevalence of leptospirosis in rodents and dogs in this region, which proves possible role of these animals in transmission of leptospires to humans. Hence it is imperative to necessary control measures to prevent human leptospirosis.
Keywords: Dog, leptospirosis, prevalence, rodent, reservoir
|How to cite this article:|
Patil D, Dahake R, Roy S, Mukherjee S, Chowdhary A, Deshmukh R. Prevalence of leptospirosis among dogs and rodents and their possible role in human leptospirosis from Mumbai, India. Indian J Med Microbiol 2014;32:64-7
|How to cite this URL:|
Patil D, Dahake R, Roy S, Mukherjee S, Chowdhary A, Deshmukh R. Prevalence of leptospirosis among dogs and rodents and their possible role in human leptospirosis from Mumbai, India. Indian J Med Microbiol [serial online] 2014 [cited 2017 Oct 22];32:64-7. Available from: http://www.ijmm.org/text.asp?2014/32/1/64/124319
| ~ Introduction|| |
Leptospirosis, the infection caused by leptospires is the most prevalent zoonosis in the world.  Evidence of reservoir status of different animals for leptospira has been demonstrated and this fact is an important factor in the persistence and epidemiology of human leptospirosis.  Rodents are the most important reservoir host and common source of infection for humans. Most of the cases of human leptospirosis worldwide have been attributed to rodents. The serovar Icterohaemorrhagiae has been often associated commonly with rodents; however, other serovars have also been isolated.  Also, the risk of leptospira infection from dogs to human and other animals is enormous. The disease, which is caused by serovars Icterohaemorrhagiae and Canicola most commonly incriminated with cases of 'classic' canine leptospirosis. It has decreased greatly with the development of commercial vaccines containing antigens from these serovars, whereas there are other serovars becoming more prevalent in producing the disease.  Reservoir hosts play important role in the transmission dynamics of leptospirosis. It is therefore important to have knowledge of the serovars present and their associated reservoir hosts in order to assess risks to humans and apply control measures.  Data reflecting the prevalence of leptospirosis in rodents and dogs in the Mumbai region has been scarce. In the view of the incidence of sporadic cases and post flood outbreak of human leptospirosis with high mortality in Mumbai during 2005, the study was carried out in Mumbai to determine the role of rodents and dogs as reservoirs of infection and to identify the prevalent serovar among them, which would be of importance to apply necessary preventive measures to control human leptospirosis.
| ~ Materials and Methods|| |
A retrospective study was carried out to determine the reservoir status of rodents and dogs for leptospirosis in Mumbai, India during 2006-2008.
A total of 60 rodents (41 Bandicoota bengalensis, 14 Rattus norvegicus and 5 Rattus rattus) were caught alive from different regions of Mumbai. The rodents were taken out of the wonder traps, identified according to their morphological characteristics and noted. Blood samples were taken by piercing the heart after anaesthesia. Suspected canine cases (n = 40) presented to the Bai Sakarbai Dinshaw Petit Hospital for Animals Parel, Mumbai with the signs of anorexia, fever, vomiting, dehydration and icterus (based on the clinician's judgment). The blood was withdrawn from cephalic vein. Serum was then separated by centrifugation and stored at -20°C until use.
A fresh urine samples were also collected from rodents (n = 12) and dogs (n = 6). Urine was withdrawn aseptically from urinary bladder with needle from rodents and using catheter from dogs. The urine was further centrifuged and the sediment was used to detect leptospiral DNA. After reviewing the research protocol, the study was approved by the animal ethics Committee of Haffkine Institute, Mumbai, India.
Serum samples of rodents (n = 31) and dogs (n = 40) were tested for leptospira antibodies by the microscopic agglutination test (MAT).  The test was carried out on all sera using a panel of 10 antigens; Australis, Bankinang, Ballum, Canicola, Grippotyphosa, Hebdomadis, Hardjp, Pomona, Icterohaemorrhagiae, Pyrogenes, Bataviae and Tarrasovi at doubling dilutions starting from 1:20; a titre of 1:80 or above was considered positive. MAT was performed by RMRC, Port Blair, Andaman and Nicobar Islands, India.
Real time PCR was performed to confirm the presence of leptospiral DNA in all serum (n = 100) and urine (n = 18) samples. DNA was extracted using the DNA Sorb-B kit (Saccace biotechnologies, Italy) as per manufacturer's instructions. The real-time PCR assay was carried out based on TaqMan® chemistry in a volume of 25 μL PCR reaction mixtures (Primer Design, UK), which specifically detects LipL32 genes of pathogenic leptospira as described earlier.
| ~ Results|| |
A total of 60 rodent serum samples were tested for the presence of leptospiral DNA using real time PCR, out of which 2 serum samples were positive. MAT was done for only 31 of the 60 rodent samples because serum condition did not allow the use of this technique for the remaining 29 cases. Out of 31 samples, 7 samples (22.6%) showed the presence of anti-leptospira antibodies. The serovar Pyrogenes was found to be predominant, accounting for six samples (85.7%), followed by the Icterohemorrhagiae, accounting for one sample (14.3%) as shown in [Table 1]. All seven positive samples were from rodent species Badicoota bengalensis.
All 40 serum samples of dogs were found to be negative for the presence of the organism by real-time PCR. Of the 40 serum samples, 7 serum samples were positive for anti-leptospira antibodies yielding a prevalence of 17.5% [Table 2]. All serum samples were predominantly positive for serovar Pyrogenes (100%).
Of a total of 71 rodent and dog samples investigated for anti-leptospira antibodies, 14 (19.7%) were positive, comprising 7 (17.5%) of 40 suspected canine leptospirosis cases and 7 (22.6%) of 31 rodents [Figure 1]. All the MAT positive rodent samples belonged to species Bandicoota bengalensis making it the most predominantly rodents species as reservoirs of infection in the study area. More significantly both the animals had Pyrogenes as predominant serovar, which proves its prevalence and epidemiological importance in the study area. Out of 12 rodent urine samples, 5 samples were positive for the presence of pathogenic leptospiral DNA. All six urine samples from dogs were found to be negative.
|Figure 1: Percent prevalence of leptospirosis in rodents and dogs in Mumbai, India|
Click here to view
| ~ Discussion|| |
Leptospires are maintained in nature by numerous sub-clinically infected wild and domestic animal reservoir hosts, which serve as a potential source of infection for humans. Some animals will recover from their first infection and then continue to shed bacteria in their urine, often for the rest of their lives.
Rodents are the most widespread and famous carrier for leptospires. In India, the natural leptospiral infection in rodent was first reported in Kolkata.  In Madurai, 46% positivity of viable leptospires belonging to the serogroups Autumnalis and Javanica in field rats has been reported. Rats and bandicoots have shown the evidence of anti-leptospiral antibodies following isolation of leptospires from suspected human patients from the suburbs of Chennai. Elsewhere, in Tamil Nadu anti-leptospiral antibodies (52.1%) were evident from the field rodents.  Antibodies to Autumnalis, Javanica, Icterohaemorrhagiae and Pomona predominated in rats (51%) in a study from southern India.  Comparatively low seroprevalence (7.1%) was observed among the rat population, yielding two isolates from the Andaman and Nicobar archipelago,  while our study demonstrated seroprevalence of 22.5% among rodents. The most predominant leptospira serovars found was Pyrogenes (85.7%) followed by Icterohemmorhagiae (14.3%).
The only serovar detected from all the MAT positive dog samples (7/7) was Pyrogenes. In the seroprevalence study conducted in peripheral areas around Chennai, India, the author also reported Pyrogenes as one of the few serovars found in dogs.  Similar observation was made in one of the studies on seroprevalence of leptospirosis in animals from Tamil Nadu, India.  While study conducted in Kerala showed that Autumnalis was predominant serovar, while pyrogene was also one of the serovars found.  Apparently, all the vaccines available locally do not contain this serovar. Hence, the present study suggests that there is a need for a change in the vaccines used against canine leptospirosis in Mumbai. It is necessary that any commercial vaccine should include the locally prevalent leptospira serovars found among dogs. Hence, it becomes imperative to do continuous active surveillance of canine leptospirosis to understand the changing epidemiology and the emergence of new serovars in dogs.
Real-time PCR analysis on all serum samples confirmed only two (2%) rodent samples positive for leptospiral DNA. This could be elucidated because probably rest of the rodents and dogs were temporary shedders and they might be in immune phase of the infection, where leptospires are found only in urine. This fact is evident from high positivity by MAT in both rodent and dogs samples. Rodents are known to be important reservoir for leptospira where they are maintained in renal tubules. While determining the reservoir status of leptospira, we found an overall rate of 41% (5/12) for the presence of leptospira in the urine sample of rodents. In one of the study conducted in Bangalore, PCR positivity of 17.65% was for rodent urine samples.  It is clear from this finding that rodents are possibly a significant source of human infection in Mumbai.
In the present study, the major prevalent leptospira serovar found in dogs and rodents was Pyrogenes. Interestingly the similar predominance of serovar Pyrogene was observed in our study carried out on human samples during the same period.  It has been speculated that the serovars present in rodents in a given environment are similar to those present in dogs living in that same environment. These findings suggest that rodents might have been the source of infection for human leptospirosis in Mumbai. This emphasises the importance of rodent control and prevents contamination of feed stuffs and water supplies with the excretions and secretions of these animals as the measures, which can be used to control human leptospirosis. In conclusion, investigating the prevalence of leptospirosis in dogs and rodents, as well as identifying the serovars responsible for an infection provides a better understanding of the role of these animals in transmission dynamics and the epidemiology of human leptospirosis in Mumbai.
| ~ Acknowledgment|| |
The authors would like to wish deep gratitude to Dr. Vijayachari, Director and Dr. Samir Sharma, Research Officer from WHO Collaborating Centre for Diagnosis, Research, Reference and Training in Leptospirosis, RMRC, Port Blair, Andaman and Nicobar Islands, India for providing laboratory support for MAT analysis. The authors would also like to thank Dr. Renu Bhardwaj, Deputy Dean and Head, Dept. of Microbiology, B.J. Medical College, Pune for her guidance and continuous support. The assistance of the Bai Sakarbai Dinshaw Petit Hospital for Animals, Bombay veterinary college and Municipal rat destruction establishment unit, Parel, Mumbai, in collection of dog and rodent samples is gratefully acknowledged.
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[Table 1], [Table 2]
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