Seroprevalence of Bluetongue in Free-range Mithuns ( Bos frontalis )

| The present study was conducted to assess the seroprevalence of bluetongue (BT) in mithun (Bos frontalis). Serum samples were collected from apparently healthy mithuns from their original breeding tract of Nagaland with free range management. Anti-BT antibodies were detected in sera using indirect enzyme linked immunosorbent assay (i-ELISA). Out of total 50 serum samples screened, 19 serum samples (38%) were found positive for the presence of anti-BT antibodies. Incidence of bluetongue in animals of Nagaland being not reported so far, the present paper reports seroprevalence of bluetongue in this bovine species indicating bluetongue virus (BTV) infection in those animals. The study indicates presence of bluetongue virus in Nagaland that warrants further studies on potent vectors and BTV serotypes circulating in the state.


Advances in
ious villages falling under three districts -Kohima, Phek and Tuensung having abundant tropical rain forests.Samples were collected from both calf (< 2yr old) and adult (> 3yr old) mithuns of both sexes separately.Collected sera were stored at -20ºC till further used.
For detection of anti-BT antibodies in serum samples, i-ELISA was performed using BTV antigen supplied from the collaborating centre of All India Network Programme on Bluetongue (AINP-BT) at IVRI, Mukteswar following the standard protocol (De et al., 2008).The reading was taken in an ELISA plate reader (ECIL, India) at 492 nm and average optical density (O.D.) values of negative control was calculated and compared with that of test samples.
Chi-square test at two degree of freedom (5%) for detection of significant difference between positive serum samples of male and female animals and that of between age group > 3yr with <2yr old was performed in SPSS version 21 (SPSS Inc., Chicago, USA).
In our study, we found an overall 38% seropositivity in this domesticated yet maintained in the wild bovine species (mithun).However, earlier report showed an overall much higher seropositivity (86%) in mithun (Rajkhowa et al., 2008).Moreover in the present study, % positivity found in male and female animals were 36.36% and 39.26%, respectively.Again younger animals of age <2-3yr had percent positivity of 37.50, but adult animals of age > 3yr had 38.46% seropositivity.The difference in % positivity between males and females or due to age variation was not significant at two degree of freedom (5%).Similar higher % positivity was observed in male (89%) and female (85%) animals as also younger (<2-3yr old) (58%) and adult (> 3yr old) mithuns (86%).This might be due to difference in tests (i-ELISA vs. cELISA) employed in these studies and areas covered for sample collection.Sex of the animals was considered in the study with the idea that virus has potential to cause abortion and BTV exposed female animals might have more seropositivity.However, as the animals were from free ranged management, authors failed to get any data on history of abortion.There was no significant difference in seropositivity in younger and adult animals.Seroconversion in form of considerable high seropositivity in younger animals might be due to vertical transmission that are apparent in bluetongue.However, horizontal transmission also cannot be ruled out.Again, as the animals were in free range system, monitoring of the animals were not possible that hindered of getting clear picture of the BT infection in those animals.High and considerable low anti-BT antibodies were found in bovines of different regions.Oberoi and co-workers (1988) (2013).Bovines are considered to be the reservoir hosts of BTV because the viraemia is prolonged and the majority of infections are sub-clinical (Maclachlan et al., 1992).These animals play an important role for dissemination of BT through potent vector-Culicoides spp.(Halder et al., 2013).The present study confirms the need of studying the vector biology of the area for better understanding the BT epidemiology of the state.It may be mentioned here that, mithun being wild and ferocious in free range form; practically it is quite difficult to get blood samples in large quantity.As such a small sample size may be considered useful for getting an indication of the alarming situation of BTV exposure in this bovine species that warrants future study encompassing the whole agro-climatic zone.
In conclusion, this study reflected the current status of seroprevalence of bluetongue infection in mithun of Nagaland although active disease outbreak/incidence has not been reported so far in ruminants of the state.The results indicated that further studies are needed to identify the competent vector(s) from Nagaland and to determine the BTV serotypes that are circulating in the state.

Table 1 :
Assessment of anti-bluetongue antibodies in serum samples of mithun by i-

ELISA Type of animal Number of sam- ples tested Positive samples Positivity (%)
*No significant difference at two degree of freedom (5%) demonstrated anti-BTV antibodies in 70% cattle sera in Punjab and Joardar et al. (2013) in Assam state.However, considerable low seropositivity (2.69%) was reported in dairy Holstein cattle of central Iran by Noaman et al.