Sample collection
A total of 1000 buffalo serum samples from 242 villages in 63 districts from top 10 milk producing states were collected (Table 1).
Enzyme immunoassay for detection of IBR antibodies
A total of 1000 buffalo serum samples were collected during 2021 and tested for IBR antibodies which showed a per cent positivity of 43.30 [44.02 (95% CI: 40.53-47.58%)] (Fig 1). Punjab showed the highest positivity of 58% [60.92 (95% CI: 49.66-71.5%)] which is a geographically a small state and known for dairy farming, whereas Andhra Pradesh showed the lowest positivity of 27% [(25.29 (95% CI: 16.4-36.13%)] (Table 1). Following four zones of India had a varied seroprevalence of IBR (Table 2).
South zone
Samples analyzed from this zone were from 3 states (Andhra Pradesh, Karnataka and Tamil Nadu). A total of 300 buffalo serum samples were tested and this zone showed seropositivity of 37% [36.78 (95% CI: 30.73-43.21%)] from 58 villages covering 23 districts. In the present study, Karnataka showed the highest seropositivity of 54% [56.32 (95% CI: 45.13-67.17%)] in buffalo samples collected from 13 villages of 7 districts. Whereas,
Renukaradhya et al., (1996) have reported 52.5% (530/1010) seropositivity in buffaloes from one slaughter house alone situated in Karnataka that seems to biased. In another study, 72.60% (106/146) seropositivity in buffaloes of two organized farms in Karnataka was recorded
(Krishnamoorthy et al., 2015). Tamil Nadu has showed 30% seropositivity [28.74 (95% CI: 19.42-39.75%)] in buffalo samples collected from 24 villages belonging to 7 districts in this study. Whereas,
Selvaraj et al., (2008) showed the seropositivity of 8.56% (16/187) in buffaloes of Tamil Nadu.
West zone
Gujarat, Maharashtra and Rajasthan were a part of this zone. A total of 300 buffalo serum samples were tested and showed a positivity of 39.67% [39.85 (95% CI: 33.67-46.32%)] from 114 villages across 14 districts. Maharashtra showed highest seropositivity of 47% [48.28 (95% CI: 37.37- 59.44%)] and Rajasthan showed lowest seropositivity of 33% [32.18 (95% CI: 22.49-43.33%)]. The three states in this zone are the highest milk producers having high yielding dairy animals. Maharashtra has recorded a highest seropositivity of 47% being geographically large state and known for dairy farming. Rajasthan being the second highest milk producing state of India has showed the lowest seropositivity of 33%. Gujarat has showed a seropositivity of 39% in buffaloes which has a good network of milk producer’s cooperative units. The buffalo samples of Gujarat were collected from 81 villages of 3 districts. 24 out of 32 (75%) buffalo samples were found positive for IBR antibodies in Gujarat
(Patel et al., 1983). Pandita and Srivastava, (1993) showed an incidence of IBR as 50.50% in buffaloes in Gujarat.
Jain et al., (2009) have tested buffalo serum samples for IBR antibodies that showed 34.61% seropositivity in Gujarat which shares borders with Rajasthan. A seropositivity of 33.69% (97/288) of IBR antibodies were recorded in buffaloes of Gujarat during 2018
(Kathiriya et al., 2018).
North zone
This zone consisted of Haryana, Punjab and Uttar Pradesh. Cumulative per cent positivity was found to be 52.33 [54.41 (95% CI: 47.92-60.83%)]. Punjab showed the highest seropositivity of 58% [60.92 (95% CI: 49.66-71.5%)]. Punjab is a small state and is a 6
th highest milk producing state of India. According to 20
th livestock census, Punjab has increased its milk production by 50.14% between 2012 and 2019
(DAHD, 2019). In the present study, a seropositivity of 58% was recorded in Punjab buffalo samples collected from 11 villages belonging to 9 districts. Previous studies have reported seropositivity of IBR antibodies in buffaloes as varying percentage.
Aradhana et al., (2004) have reported 33.3% of seropositivity of IBR in buffaloes of Punjab. In another study,
Dhand et al., (2002) have recorded 47.25% (43/91) and 17.47% (43/246) of seropositivity of IBR antibodies in organized and unorganized buffalo farms respectively in Punjab. A small number buffalo serum samples from Ludhiana (Punjab) were tested for IBR antibodies which showed the positivity of 54.50% (12/22)
(Dhami et al., 2008). The lowest seropositivity of 48% [49.43 (95% CI: 38.47-60.56%)] was recorded by Haryana. Uttar Pradesh showed 51% seropositivity [52.87 (95% CI: 41.78-63.88%)].
Uttar Pradesh is the largest state of India and is the number one in milk production. The state has recorded a seropositivity of 51% of IBR antibodies in buffaloes of 8 villages from one district only. The sample number should have been more which was not accomplished due to administrative reasons. A small number of buffalo serum samples tested in Uttar Pradesh revealed 85% (17/20) positivity by
Nandi et al. (2011).
Verma et al., (2014) have recorded 25.27% (23/91) seropositivity of IBR in buffaloes of 8 districts of Uttar Pradesh.
Central zone
Madhya Pradesh is the only state in this region which is geographically large in nature. The state has showed a seropositivity of 46% [47.13 (95% CI: 36.28-58.32%)] in buffaloes from 5 villages of 2 districts. The Chhattisgarh state which was a part of Madhya Pradesh previously, have reported a seroprevalence of 7.15% (3/42) in buffaloes
(Samrath et al., 2016). Madhya Pradesh shares a border with Maharashtra (seropositivity: 47%), Gujarat (seropositivity: 39%), Rajasthan (seropositivity: 33%), Uttar Pradesh (seropositivity: 51%) and Chhattisgarh (seropositivity: 7.1% by
Samrath et al., 2016).
Breed wise seropositivity
Murrah is the most important breed of buffalo in India. Murrah’s home is Haryana and Punjab states and the average milk yield per lactation is 1500-2500 kilograms. A seropositivity of 44.08% of IBR antibodies were reported in Murrah breed. Mehasana’s home is Gujarat and Maharashtra states and is evolved out of cross-breeding between Murrah and Surti. Murrah and Mehsana were two important breeds of buffaloes along with non-descript buffaloes were tested for IBR antibodies (Table 3). 44.08% (320/726) [44.92% (95% CI: 40.81-49.09%)] seropositivity was recorded in Murrah breeds and Mehsana breed recorded 40.48% (34/84) [40.78% (95% CI: 29.45-53.06%)] seropositivity. Non-descript (not assigned any breed characteristics) showed 41.24% (73/177) seropositivity [41.66 (95% CI: 33.62-50.12%)]. Mehasana buffaloes showed a IBR seropositivity of 40.48%. There were some buffaloes which were non descript in nature showed 41.66% seropositivity.
Krishnamoorthy et al., (2015) have shown an incidence of 69.15% (92/133) and 66.67% (4/6) in Murrah and Mehasana buffaloes respectively in south India.
Kathiriya et al., (2018) have reported a seroprevalence of 33.99% in Jafrabadi breed in Gujarat. Very limited reports are there on seropositivity of IBR breed wise in India.
India is the world’s largest milk producer, with 22 per cent of global production. Top 10 milk producing states of India contribute to 80% of the national milk production. Additionally, India stands first in the world of buffalo population contributing significantly to the milk production of the nation. India has 109.9 million buffalo (adult female buffaloes: 55 million). Therefore, an attempt was made to screen one hundred buffalo serum samples for IBR antibodies, collected randomly from top 10 milk producing states. Many authors in India and elsewhere have reported seropositivity of IBR antibodies in buffaloes taking limited number of samples. The present study has revealed seropositivity of IBR antibodies in buffaloes in 100 samples from each top 10 milk producing states of India. Overall seropositivity of IBR antibodies in 1000 buffaloes was found to be 43.30% in India. Buffaloes are domesticated in limited number of countries and many of them have reported seroprevalence of IBR antibodies in buffaloes. A 16.7% (6/30) and 51.50% (103/200) prevalence of IBR in buffaloes was recorded in Pakistan
(Akhtar and Asif, 1996; Batool et al., 2022), wherein the number of buffaloes screened in both the studies appeared limited.
Mahmoud et al., (2009) have demonstrated 38.46% (5/13) seropositivity of IBR antibodies in buffaloes in Egypt. A seroprevalence of 82.40% (155/188) of IBR antibodies was recorded in Murrah and Mediterranean buffaloes in Brazil
(Ferreira et al., 2010). The two studies in Iran have showed a seroprevalence of 5.5% (28/513) and 4.13% (5/121) of antibodies against IBR in buffaloes
(Lotfi et al., 2016; Kargar Moakhar et al., 2002). In Iraq,
Ahmed et al., (2015) have reported 73.9% (17/23) seropositivity of IBR antibodies in buffaloes.
Trangadia et al., (2010) have reported seroprevalence of IBR antibodies in organized buffalo farms located in three zones of India
viz., Western region reported 40.82% (20/49), Central region has revealed 97.96% (48/49) and Northern region has recorded 26.32% (5/19) and overall seroprevalence was found to be 62.39% (73/117).
Age wise seropositivity
In the present study, the buffaloes in age group between 11-15 years showed the highest seropositivity of 50% (15/30). 688 buffaloes in the range of 5-11 years of age were tested and 42.01% (308/688) of animals showed seropositivity (Table 4). Animals with 3-6 years of age were more prone to infection than were younger animals and the seropositivity of IBR increased with age of animals
(Nandi et al., 2009). The highest prevalence of IBR (42.07%) was observed in animals aged more than 7 years
(Kathiriya et al., 2018).
Mahmoud et al., (2009) have showed seropositivity of IBR antibodies in different age groups as buffaloes of 3-6 m having 40%, 3-16 m having 33% and adult buffaloes having 40% in different parts of Egypt. Animals above 9 years of age showed the highest seropositivity (45.9%) whereas young animals between 0 to 2 years of age showed the minimum seropositivity (6.89%)
(Samrath et al., 2016). Increased age has been considered a risk factor for higher prevalence as a result of greater chances of virus exposure to susceptible animals with age and a study noted that BoHV-1 is more prevalent in animals greater than 4 years
(Batool et al., 2022). Lowest seroprevalence of IBR was found in buffaloes below 2 years of age and highest in animals of above 8 years of age
(Dhami et al., 2008). Kathiriya et al., (2018) showed maximum seropositivity of IBR in animals of more 7 years of age. The incidence of IBR was recorded more as the age of animals increased
i.
e., 6 years and above
(Krishnamoorthy et al., 2015) might be due to increased susceptibility and stress.
The possible reason for higher seropositivity may be due to increased susceptibility of animals with age or repeated subclinical infection with the virus that boost to keep the antibody titer higher enough to be detected positive or decrease in immunity and increase in stress, which may lead to reactivation of latent virus
(Singh and Sinha, 2006; Kathiriya, 2018; Sheza et al., 2021).