6.3 Availability of tick vectors
Soft ticks (Acari: Argasidae ) are important vectors of disease-causing pathogens in human and animal populations including wild animals (de la Fuente et al., 2008). Previous studies have shown that the infected Ornithodoros ticks are able to retain the virus for long periods thus serving as a biological vector and transmit it to susceptible hosts (Plowright et al., 1994). In addition, members of Ornithodoros species can transmit ASFV from tick to tick through transstadial (Hess et al., 1989), sexual and transovarial transmission (Plowright et al., 1970) allowing the virus to persist even in the absence of viraemic hosts. Endemism of ASF in any country may depends upon the prevalence and geographical distribution of Ornithodoros species. In India, the prevalence of soft ticks has been found to be comparatively lower than hard ticks (Shyma et al., 2019). This might be because of limited studies on soft ticks especially on Ornithodoros species to even identify their geographical distribution. Ornithodoros ticks has been associated with transmission of ASF, Karshi virus or Langat virus associated encephalitis (tick-borne encephalitis virus complex) and Human relapsing fever (Manzano-Román et al., 2012). Among these diseases, louse borne human relapsing fever has been initially discovered in India in 1907 with the association of Pediculus humanus  in the transmission of the causative agentBorrelia recurrentis (Mackie, 1907). Later a few case reports on tick borne human relapsing fever has been reported from Indian states of Kashmir (Kalra and Rao, 1951), Madhya Pradesh (Aher et al., 2008) and Karnataka (Veena et al., 2013) confirming the involvement of Ornithodoros ticks in their transmission. The present outbreak of ASF in India is still not known in the context of transmission involving tick vectors/biting flies/infective secretions and tissues or possibility of indirect transmission by fomites. Since, Ornithodoros species have already been found to be associated with other diseases and its prevalence has been reported from Gujarat (Sharma et al., 2017; Shyma et al., 2019), Nilgiri Hills and adjoining areas of Tamil Nadu (Kumar et al., 2014), there may be a possibility of involvement of Ornithodoros species with the present outbreak of ASF in the NE India. The paucity of research on prevalence of Ornithodoros ticks and their probable role in the transmission of various diseases of animal and public health importance in the country might further enhance the possibility of further outbreaks of ASF in other pig rearing states of India.