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.