Biology Reference
In-Depth Information
One important vector of B. bigemina is Boophilus microplus. With regard to mor-
tality and morbidity, these two diseases are probably comparable to malaria in
humans in India.
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Bacterial Diseases
The important bacterial tick-borne disease of man and animals in India is the
relapsing fever caused by spirochaetes. Human infections with spirochetes are
known in the northern colder parts of India, particularly in Kashmir. The disease is
caused by Borrelia persica and is transmitted by the Argasid ticks, Ornithodoros
tholozani. The natural reservoirs are rats, mice, and other rodents. The disease is
clinically characterized by recurring bouts of fever separated by a febrile interval
of 9
10 days. But the mortality rate is rather low. Army personnel working in the
endemic areas are prone to the disease. Use of several synthetic insecticides like
BHC, diazinon, dichlorovas, and Malathion is feasible and has been recommended.
Tularemia, a plague-like disease, caused by Francisella tularensis and carried by
Dermacentor sp. or Amblyomma sp. occurs in many parts of the world, including
the USA, Canada, USSR, Japan, and southern Europe, but there are no reports of
its occurrence in India so far.
Viral Diseases
There are a number of arboviruses which are known to be transmitted by Ixodid
and Argasid ticks. Most of them have animal reservoirs either in domestic animals
or in field animals in the natural environment. All over the world, over 80 such
viruses have been recorded with tick involvement. However, in India the isolation
of viruses from ticks and their hosts has been restricted only to a few areas.
Kyasanur Forest Disease (KFD)
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This is the most important tick-borne viral disease in India. It was first recog-
nized in 1957 in the forests of the Shimoga district of Karnataka state as a fatal
infection of monkeys and subsequently as a serious disease in man. It is still
restricted to the same general area, but with some local extensions along the neigh-
boring districts like north Kanara, South Kanara, Chikkamagaluru, and Udupi. The
disease in man varies considerably from mild pyrexia for a few days to serious ill-
ness with hemorrhagic manifestation leading to death. The virus has been isolated
in nature from man and monkeys and several species of ticks. The virus seems to
be unusually hardy, capable of being isolated from blood or tissues several days
after collection and transportation on ordinary ice.
The mammalian hosts other than man are also of many and varied types.
Monkeys of two species present in the region, namely Presbytis entellus and
Macaca radiata, are highly susceptible. Monkeys get infected by bites of larvae
and nymphal stages of ticks, mostly of the genus Haemaphysalis sp. While the
P. entellus monkey normally succumbs to the infections, the M. radiata monkey
shows a certain degree of ability to overcome the disease and to survive. It is the
infection and death of monkeys in the forest that generally heralds the epidemic
season and the activity of the virus in the locality. The incidence in man coincides
with the season of the prevalence of the nymphs of Haemaphysalis, that is gener-
ally December to March and occasionally up to June. KFD infects many species
