The species distribution of ticks & the prevalence of Kyasanur forest disease virus in questing nymphal ticks from Western Ghats of Kerala, South India

Abstract

Background & objectives: Kyasanur forest disease (KFD) is a zoonotic tick-borne disease across the Western Ghats of India. With the discovery of a cluster of human KFD cases in the Wayanad district of Kerala, the present study was focused on detecting KFD virus (KFDV) in tick populations. To manage this disease, it is necessary to understand the diversity of the tick species and factors influencing the distribution, abundance and prevalence of infected ticks in Wayanad district.

Methods: Surveys were conducted from November 2016 to May 2018 in four forest ranges of Wayanad district. Ticks were collected by the dragging method and were identified to species level and assayed for virus detection using real-time polymerase chain reaction.

Results: A total of 25,169 ticks were collected from 64 sites. Of the identified species, Haemaphysalis spinigera was the most abundant (56.64%), followed by H. turturis 9047 (35.94%), H. bispinosa 999 (3.96%), Amblyomma integrum 691 (2.74%), H. kyasanurensis (0.55%), Rhipicephalus sanguineus (0.08%), Hyalomma marginatum (0.02%), H. cuspidata (0.01%), R.microplus (0.01%) and Dermacentor auratus (0.003%). The nymphal stage was predominant from December to February having peak activity in January. A total of 572 pools were screened for the presence of KFDV, of which 21 pools were positive. The infection rates in H. spinigera and H. turturis tick were 2.62 and 1.04 per cent, respectively.

Interpretation & conclusions: The circulation of KFDV was detected and its correlation with the prevalence in ticks near the fragmented forest and teak plantation areas of Wayanad district. Residents and visitors of these regions may become vulnerable to tick bites and to an increased risk of KFD as the distribution of established, infected tick populations continues to expand.

Keywords: Climate; Haemaphysalis spinigera; Kyasanur forest disease; Wayanad; forest; pool; ticks; virus.

Fig. 1

Spatial distribution map of host-seeking nymphal ticks in four forest ranges of Wayanad district. 1. Muthanga (Zone 1), 2. Sulthan Bathery (Zone 2), 3. Kurichiyat (Zone 3) and 4. Tholpetty (Zone 4), forest ranges from which obtained tick samples has been highlighted in different colours. The location of the positive sample for Kyasanur forest disease is marked with a red colour. Source: Kerala forest department, Sulthan Bathery, Wayanad district, Kerala.

Fig. 2

Seasonal density of Haemaphysalis turturis, Haemaphysalis spinigera and total ticks with respect to climatic factors from Wayanad district.