Mithun (Bos frontalis), a rare bovine species inhabiting the north-eastern hilly region (NEHR) of India, immensely contributes to the local tribal economy holding an important position in the social, cultural and religious life of the local community¹. Being a vulnerable species, International Union for Conservation of Nature duly considers the conservation of mithun as immensely essential for India having a diverse climatic situations². Foot and mouth disease (FMD), endemic in India, is caused by FMD virus (FMDV) serotypes O, A and Asia 1. It is one of the significant constraints in the way of mithun and yak farmers in the NEHR and is reported as one of the main reasons for the decline in the mithun population of Nagaland and Manipur³. FMD is reported as a menacing disease in these species with considerable mortality in young animals⁴. Moreover, frequent FMD outbreaks in mithun and yak have been reported during previous instances⁵, ⁶. To cite a few, during 2009, two outbreaks due to serotype O occurred in Mizoram, causing high mortality in mithun population. Many outbreaks in yaks and hybrids of yak with local cattle have also been reported in different parts of Nepal⁷, ⁸.

The global mithun population is estimated at 0.5 million heads⁹. India has the largest mithun population (nearly 97.57%) in the world¹⁰. According to the 20^th Livestock Census by the Department of Animal Husbandry and Dairying, the total population of mithun in the country during 2019 was 390 thousand heads and total yak was 58 thousand heads. The highest population of mithun is found in Arunachal Pradesh state constituting around 90% of the total mithun population, followed by Nagaland, Manipur and Mizoram³. Despite being the main support of the tribal economy of the NE region, mithuns and yaks have generally been ignored with respect to disease control measures that has predisposed them to many infectious diseases⁵. The present study reports FMD caused by serotypes O and A along with the demonstration of infection-specific antibodies in mithun, yak and cattle-yak hybrids in the north-eastern region of India during 2021-2022 that can highlight the importance of prevention of FMD in these species.

During the year 2021, a number of suspected cases of FMD were reported in the cattle population which were confirmed in the containment laboratory at ICAR-NIFMD, Bhubaneswar¹⁵, ¹⁶. Also, several outbreaks were reported in different districts of Arunachal Pradesh and an organized farm of Nagaland. Mithun and cattle from Arunachal Pradesh were reported with suspected FMD incidences and subsequently got laboratory confirmed. The affected animals under investigation exhibited clinical signs of fever, inability to take feed, smacking of the lips with foamy and ropy salivation (Fig. 1) with lameness. Gross erosive lesions in the nasal region (Fig. 2), erosive lesion in palate region with foamy saliva on tongue in the oral cavity (Fig. 3), initial erosive lesions on the muzzle/planum nasolabiale with salivation in the affected mithun (Fig. 4), severe erosive lesions on the muzzle and nasal region with secondary maggot infestation (Fig. 5), erosions on tongue (Fig. 6) and that in the interdigital space and around the hoof suggestive of FMD were observed. Out of 11 clinical samples from mithuns and 5 cattle from Arunachal Pradesh tested in serotyping sandwich ELISA and RT-multiplex PCR, 2 samples from mithun and 1 from cattle were found positive for FMDV serotype O (Fig. 7). Before the present outbreak, FMD incidences in mithun caused by serotype O were reported during 2010 and 2011 in Arunachal Pradesh. Two samples of mithun from the organized herd from Nagaland state were found to be positive for serotype A (Fig. 7). This present study of FMD outbreak in mithun reminds an FMD outbreak long before due to serotype A in Sikkimese yak during 1973¹⁷. Along with the clinical samples from the affected animals, a total of 35 (10.6%) of 330 sera from mithun, 10 (3.83%) of 261 from yak and 5 (16.67%) of 30 from cattle-yak hybrids were found positive for 3AB3 NSP antibody in the indirect ELISA.

During the year 2021, relatively higher numbers of FMD outbreaks were reported in the bovine population in different states in the country compared to preceding years. Mithun and yak being semi-domesticated species, come in contact easily with cattle and the cattle-yak hybrids along with the small ruminants especially goats reared in north-eastern part of the country. Such close proximity and interactions of different susceptible animals in common habitats and grazing areas, even during shelter in the same house or shed might have triggered the spread of infection in these species. Apart from mithun, FMD (due to serotype O) has also been reported in yaks of Himachal Pradesh¹⁸, where the animals were in frequent contact with cattle, sheep and goats being the residents of the districts bordering Tibet. In forest areas with frequent habitual nose-to-nose contact between the infected mithuns and yaks, the disease spreads to a greater number of animals. The contact of mithun and yak with migratory cattle has been predicted to have an important role in spreading the disease to these semi-domesticated animals as reported before⁶. Furthermore, because of their habitats in difficult and unapproachable forest areas, diseased yaks and mithuns are neither usually attended by the veterinarians nor the healthy animals are vaccinated against FMD thereby collectively making the animals more prone to the disease.

The Government of India is on move with the practice of routine FMD vaccination campaign in cattle and buffalo population under the livestock health and disease control programme (LHDCP) in all the states and UTs of the country, while other species have not yet been targeted for vaccination. Spillage of virus from primary hosts like cattle and buffalo to semi-domesticated populations of mithun and yak as well as their hybrids in hilly terrains of north-eastern regions is of high concern from the point of view of prevention of infectious diseases like FMD as well as the conservation of biodiversity in the region. In order to prevent the disease in these species, there is a need for regular serosurveillance and rigorous vaccination strategy in the population of mithun and yak along with cattle at regular intervals that may help in breaking the virus transmission cycle. Vaccination with 100% coverage of semi-domesticated mithun and yak population at the interface of domestication is again the most vital part of FMD management⁴. Besides all these, all the stakeholders should be made aware of the clinical symptoms of FMD to promptly report the disease occurrence to the health authority along with benefits and importance of vaccination in animals for disease prevention and control.

From the present investigation and findings as well as from the earlier reports, it is clear that FMD in mithun and yak may be due to negligible herd immunity due to no/sparse vaccination, unrestricted animal movement, as well as frequent mingling of different susceptible animals in common grazing pasture land. Biosecurity practices are really very difficult to execute in habitation where mithun and yaks inhabit. Apart from this, mithun and yak being rare and unique bovines, should be given more attention on the prevention of infectious diseases like FMD with a planned vaccination strategy combined with other tools of surveillance and monitoring, as is routinely practiced for cattle and buffalo populations under national animal disease control programme in place in the country by the government of India.

Continuous vigil at domestic-wildlife interface along with effective immunization in this zone is likely to be an effective strategy for FMD control in these species which are very important for preservation of biodiversity and sustenance of local livelihoods of the tribal community of the north-eastern region of the country.

References