Tehsil wise
Leptospira seroprevalence in cattle and goat of ANI is spatially analysed to prepare maps (Fig 1 and 2). The result of seroprevalence among the cattle and goat species were similar. However, the percentage of positive samples was found to be more in goats compared to cattle. In cattle, no significant difference could be found between age, sex and region in the seroprevalence of
Leptospira or for any of the serovars. In the case of goats, overall seroprevalence across the regions was similar while the seroprevalence of serovars Icterohaemorrhagiae AF61, Icterohaemorrhagiae GFA were significantly (p<0.05) high in Rangat Tehsil of North and Middle Andaman district. Seroprevalence of Grippotyphosa CH31 was significantly high (p<0.08) in the Ferrargunj Tehsil of the Andaman and Nicobar Islands. A total of 62 sera samples showed more than 1: 40 titer ( CI: 24.7-37.9%) in both cattle and goats (Table 2). However, the goat sera samples showed the highest seroprevalence compared to cattle. The MAT titer ranged from 1:40 to >1:320, with geometric mean titer ranging from 1:40 (Hardjo) to 1:240 (Hebdomadis) (Fig 3 and 4). In the case of cattle, the frequency of percent positive was found to be highest against Icterohaemorrhagiae (19.05%) followed by Pyrogenes (11.9%), Grippotyphosa (11.9%), Hebdomadis (7.14%) and Pomona (7.4%). Other serovars showed less than a 5% prevalence rate. In goats, the highest frequency of seroprevalence was found against Icterohaemorrhagiae (16.67%), followed by Grippotyphosa (13.89%), Pomona (9.72%), Australis (8.33%), Hebdomadis (8.33%), Autumnalis (6.94%) and Pyrogenes (5.56%) (Table 3). In cattle, none of the samples showed positive against Autumnalis and Australis, while Ballum showed less than 5% prevalence. In goats, none of the samples showed positive against serovar Ballum. The most reactive serovars were Lai-like (6.2% to 15%), followed by Icterohaemorrhagiae (4.6% to 12.7%), Grippotyphosa Moskva V (4.3% to 12.1%), Grippotyphosa CH-31 (3.5% to 10.87%), Pomona (2.4% to 9.0 %), Pyrogenes (2.1% to 8.4%), Hebdomadis (2.1% to 8.4%), Australis (1.4% to 7.1%), Canicola (0.8% to 5.7%), Bangkinag (0.8% to 5.7%), Hardjo (0.3% to 4.3%) and Ballum (0.1% to 3.6%) in both cattle and goat.
Samples having multiple reactions with more than 2 serovars were more in goats (57) than cattle (25) with overall multiple seroreactivity of 71.92% (Table 4). The highest seroreactivity was found in one sample in goat from Rangat tehsil which showed multiple reactivities with 8 serovars. The serovars which showed maximum reactions were Icterohaemorrhagiae Lai-like (20), Grippotyphosa (16) and Icteroharmorrhagiae RGA (15). Multiple reactivities were observed to be more in goats compared to cattle. Multiple reactivities to more than 3 serovars were detected in 15.79% of the goat samples.
The study was conducted with the main objective to evaluate the prevalence rate of leptospirosis in cattle and goats in ANI. As representative samples, a total of 100 samples each from cattle and goats were screened for the presence of leptospiral antibodies against 12 different serovars. The result indicates that there is a moderately high seroprevalence (31%) of leptospirosis with single or multiple serovars. Leptospirosis is highly endemic in ANI with reports of a high sero-prevalance rate as well as isolation of the causative organisms (
Sehgal, 2000;
Sunder et al., 2018; Sharma et al., 2003; Mitra et al., 2015). Livestock, mainly cattle and goats plays an important role in the epidemiology of the disease in ANI. The seroprevalence in both species (cattle-28%, goat -34%) was found to be very high. The goat population is highest in these islands and is distributed to all three districts
(Sunder et al., 2018). However, the cattle population is mainly concentrated in the South and North and Middle Andaman districts of these islands. Cases of
Leptospira have been reported mainly from the North and Middle Andaman followed by South Andaman districts (
Vijayachari et al., 2003;
Sharma et al., 2006). No significant differences were noted in terms of age, sex and region in the case of cattle. Spatial distribution indicated that there was significantly high seroprevalence recorded in the ecoregions of Ferrarrgunj and Rangat Tehsils. The high seroprevalence in cattle and goats from these regions might be due to several factors such as the high concentration of cattle and goat population, agricultural activities, common grazing area and exposure to rodents. Rat plays a significant role in the transmission of the disease in animals and humans. The carrier animals transmit the organisms through the contaminated urine to the other animals. Earlier reports also support that there is seroprevalence of leptospirosis in rats
(Sharma et al., 2003). The topography of the ANI is undulating and due to high rainfall, there is stagnation of water after the monsoon. The favorable climatic conditions facilitate the survival of leptospires and act as a source of infection to humans as well as to animals. All these factors along with weather attributed to the high sero-prevalance of leptospirosis in the ANI.
The most common positive serovars in both cattle and goats were found to be Icterohaemorrhagiae Lai like (17.54%), Grippotyphosa (14.03%) and Icterohaemorrhagiae RGA (13.15%). The results are in agreement with the previous studies, in which the most common serovars were found to be Grippotyphosa
(Sharma et al., 2003), Autumnalis, Hardjo
(Mitra et al., 2015), Grippotyphosa, Icterohaemorrhagiae, Hebdomadis
(Sunder et al., 2018). In all the previous studies, the common serovar was found to be Icterrohaemorrhagiae and Grippotyphosa. Serogroup Grippotyphosa is considered one of the most common serogroups infecting human beings. The high seroprevalence of Grippotyhosa from cattle and goat in the present studies is alarming as the livestock acts as a carrier of
Leptospira and sheds organism and contaminate the environment
(Jeyakumar et al., 2002; Sunder et al., 2005). Sharma and co-workers also reported high sero-prevalance of leptospirosis in cattle (34%) and goats (29%)
(Sharma et al., 2006). They also reported that the most common serovars were Icterohaemorrhagiae, Hebdomadis and Grippotyphosa from the cattle. In the present study also, a high seroprevalence rate of leptospira in cattle and goats was reported. In our studies also, similar results were obtained as the seroprevalence in cattle was 28% and the goat was 34% respectively. This suggests that there have not many changes in the serovars affecting the livestock.
Environment plays a major role in the epidemiology of leptospiral infection. The hot, humid and high rainfall conditions of the ANI highly favours the multiplication of
Leptospira in this region. Previous studies from these islands as well as from different parts of the India and world suggest that the disease is mainly prevalent in the island and coastal regions
(Schafbauer et al., 2019; Dhivahar et al., 2019). The seasonal outbreak of leptospirosis is usually reported from the coastal areas of Tamil Nadu, Kerala, Gujarat, Maharastra and ANI (
Karande and Thakarae, 2002;
Sehgal et al., 1995; Arumugam et al., 2011). Generally, the antibodies remain in the blood for a longer period after the systematic infection. The detection of antibodies did not mean that the animals were infected or were recently infected. However, these animals may act as reservoir host or carrier host and usually transmit the leptospires to other healthy animals. In the present study, more than 31% of the surveyed animals were found to be exposed to leptospires. The animals affected with leptospires continue to excrete bacteria through the urine for up to several months
(Sharma et al., 2003). The high sero-prevalance is an indicator that the
Leptospira are in circulation in cattle and goats and there is always a high risk of contracting the infection from animals to the human being. Therefore, continuous and routine examination of the animals is very much important to develop suitable preventive measures to contain and control leptospirosis in both humans and animals.
The present study reports the prevalence of multiple serovars in cattle and goats, as 20.97% of the animals showed the presence of more than 3 serovars. Our findings are in accordance with the earlier report
(Sharma et al., 2003), wherein, 15.13% of the total tested samples showed multiple reactivities to more than 2 serovars. They also reported the common serovars as Grippotyphosa, Icterohaemorrhagiae, Pomona and Australis. In another study, similar observation of multiple reactivity in 36.5% of the samples were reported
(Schafbauer et al., 2019). Cross-reactivity in
Leptospira is very common since many serovars share a common antigen and there is a high probability of cross-reaction. The distribution of similar serovars in both cattle and goats indicates that the same strains are circulating within the same ecoregions. The epidemiology of leptospirosis is very complex, as the animal/human will show multiple infections with different serovars. In our present study, goat samples showed more cross-reactivity compared to cattle. This might be due to the recent infection and production of IgM antibodies. Reports suggest that IgM antibodies contributed to a certain degree of cross-reactivity
(Schafbauer et al., 2019). Sometimes, after the infection, there is a high rise of IgM antibodies which may persist for a longer period in the blood. Due to this, the MAT titer might be more, however, without exhibiting any clinical symptoms. The high titer does not necessarily indicates infection, however, the animals might have been exposed to leptospires
(Blanco et al., 2016). Mixed infections with different serovars were also reported by many researchers
(Sunder et al., 2018; Tripathy et al., 1985; Balakrishnan, 2012;
Vihol et al., 2016). They have reported multiple infections in goats with serovars
viz., Australis, Hardjo, Hebdomadis, Icterohaemorrhagiae and Pomona.
Out of the total positive samples, the distribution of leptospira with a titer of 1:160 was more (41.23%), followed by the titer of 1:80 (28.07%), 1:40 (15.79%) and 1: 320 (14.91%) respectively. In the previous study conducted on these islands, the highest titer was recorded as 640 from the Andaman Islands and 160 from the Nicobar Islands
(Sharma et al., 2003). However, in the present study, the samples showing a titer of more than 1:320 was found to be more. Vaccination against leptospirosis in animals in these islands is not practiced. The high titer of more than 1:320 indicates a recent infection. As per the OIE Terrestrial Manual 2021, a titer of 1:100 is taken as positive, however, because of the high specificity of the test, we have considered 1:40 as the positive titer with evidence of previous exposure. In our study, the percentage of positives in 1:160 and 1:320 was more in goats (63.89%) compared to cattle (42.86%). Most of the MAT titers were low (1:40), which might be due to exposure to earlier infection or circulation of antibodies in the sera without showing any clinical manifestation of the disease. Serotypes that showed a high titer of more than 1:320 were Grippotyphosa, Hebdomadis, Icterohaemorrhagiae and Pyrogenes. The high titer could be due to reinfection with leptospira and the continuous production of antibodies in the sera. On the island, vaccination is not practiced, so the question of high antibodies due to the vaccinal antibody response is ruled out. As MAT is generally very useful in the diagnosis of acute leptospirosis infection in animals. Animals with a titer of 1:40 (15.79%) are considered low titers or low states of infection. The animals with low titer generally act as a carrier and are the source of infection to other healthy animals. In the present study, none of the animals exhibited any clinical manifestation of the typical leptospira infection. Usually, the carrier animals are regarded as apparently healthy animals without showing any clinical symptoms. Serological test, especially the microscopic agglutination test is considered the gold standard test for the diagnosis of leptospirosis by OIE. Local strains which are prevalent in this island have been used in this study. The use of local strains ma have increased the sensitivity of the test. The specificity of the test is also good, as the leptospira usually does not cross-react with other bacteria. However, there is cross-reactivity among the different serovars. Therefore, in our study, multiple reactivities with more than two serovars are reported in goat and cattle samples. As per the reports, only a few serovars will be endemic in a particular zone or region and each serovar tends to be maintained in a specific maintenance host.
L. hardjo infection is mainly reported and maintained in cattle hosts. In ANI, the common serovars which are reported from this regions are Icteroha emorrhagiae, Pomona, Grippotyphosa, Hebdomadis and Hardjo
(Vijayachari et al., 2003; Sharma et al., 2006). Serogroup Grippotyphosa has been reported as the commonest infecting leptospira in ANI.
Surveillance and monitoring are considered important strategies for the prevention and control of any diseases. In ANI, leptospirosis is endemic and for many decades the disease has been reported in animals and humans. Cases of leptospirosis have been confirmed through clinical symptom, isolation, identification, molecular diagnosis, serology, MAT,
etc. MAT is still used as the standard test for the diagnosis of leptospira l infection. However, a single MAT titer does not necessarily confirm the current clinical infection as past infection against the circulating serovars could develop microscopic agglutinating antibodies which are long-lasting (several years). A MAT titer of 200/400 would provide the presumptive diagnosis of leptospirosis with compatibility of clinical signs and symptoms. However, negative MAT results <1 in 20 do not necessarily rule out the disease as microscopic agglutinating antibodies usually appear in the blood at a detectable level during the end of the first week or early second week of the infection. Therefore, MAT negative samples need to be tested using RT-PCR to confirm or rule out the disease. Serogroups Grippotyphosa and Icterohaemorrhagiae have been reported as the commonest serogroup in cattle and goats. An earlier study also supports the findings
(Sharma et al., 2003; Raj et al., 2018). The same serogroup is also responsible for leptospirosis in humans. Considering the potential to infect multiple species, the one health approach would be taken as the topmost priority in routine surveillance, monitoring and thereby appropriate action plan to contain and control the infection.
