Kyasanur forest disease and the bird migration study of the Bombay Natural History Society

2 Pages·1996·1.4 MB·

by  A N D Nanavati

KYASANUR FOREST DISEASE AND THE BIRD MIGRATION STUDY OF THE
BOMBAY NATURAL HISTORY SOCIETY
A.N.D. Nanavati1
In the mid 1950s a new disease was reported in who had been interested in the migration of birds,
the Kyasanur Forest area ofKarnataka State, causing was requested to undertake the study for the WHO,
high fever and other symptoms among infected and the Virus Research Centre was entrusted with
persons. In addition, there were reports of dead the study of insect parasites and viruses, if any,
monkeys found in the forest. These reports carried by them. A five year study was planned and
setoffan alarmreaction fromPublicHealthauthorities. a grant for this was made to the BNHS with S£lim
Monkey deaths in the forests of Africa often Ali as chiefinvestigator. Aseries oftrapping stations
preface an outbreak of Yellow Fever. There is no were set up at various places favoured by migrating
Yellow fever in Indiabut we have all the ingredients birds. The birds were trapped in mist nets, carefully
necessary for it to flourish. The insect vector, the removed, identified and measured. Insects attached
Aedes aegypti mosquito is common; climatic and to them were removed by combing. These were
environmental conditions similar to those in Central appropriately labelled and carried to the Vims
Africa are found in manyparts ofIndia. Yet wehave Research Centre for further study and detection of
not had any outbreaks. There is a possibility that we viruses. The birds were then tagged with a
have some factor or factors which inhibit the spread lightweight aluminium ring bearing an identifying
ofYellowFeverVirus, butuntil such factor or factors number (entered against the bird’s details in the
are recognized it behoves the Indian health record), and was then released.
authorities to be always on guard. TheBNHS exerciseditsusualcareandeconomy
Accordingly, the Virus Research Centre in forthesestudiessothatwhen thefiveyearperiodended
Pune, specialized in insect or arthropod borne virus there was enough money left to continue for a further
diseases, was asked to investigate the outbreak. three years. The WHO meanwhile had lost interest.
It was soon established thatthiswasnotYellow Since no virus infected birds or insects were found
Fever, but was caused by a hitherto unknown virus among the thousands trapped every year was
it
which was named Kyasanur Forest Disease Virus. concluded that if at all such transfer of infection
This KFD virus was found to be closely allied to the occurred, it mustbe a rare and aberrant phenomenon,
virus of Russian Spring Summer Encephalitis notjustifyingtheeffortofcontinuous monitoring. The
(RSSE) which occurs in Siberia and regions around VirusResearchCentrealso, having identified the new
Lake Baikal. Every year thousands of birds from virus and established that it was transmitted by a tick
arctic and subarctic regions migrate south to winter usually found in the forestundergrowth, whichin turn
in warmer areaswhere food and shelter areavailable. infected animals in the forest and sometimes humans,
Many of those from Siberian regions come and lost interest in migrating birds. The rest of the study
winter in India. Could it be that migrating birds was therefore confined to the study ofbird migration.
carried the virus from Siberia to India?
To resolve this question the World Health Results
Organisation planned a study of migratory birds
coming to India, and oftheir insect parasites, ifany, Migration: About 1,50,000 birds of various
which could transmit the disease to new hosts. species were trapped and studied during this period.
Salim Ali, the leading ornithologist of India, The routes taken by different species could be
studied. Most ofthem travelled eitherby theEastern
'5, Sundervan Rats, Mitha Khali, Rasala Marg,
Ahmedabad-380 006. route via Assam, Bangladesh and down the East
512 JOURNAL, BOMBAYNATURALHIST. SOCIETY, Vol. 93(1996)
Coast or by the Western route over Afghanistan, Discussion
Pakistan, Saurashtra and the West Coast. During
winter there was a large conglomeration ofall these The question of the origin of KFD virus
birds in and around several water bodies in South remains. Two facts should be considered.
India and Sri Lanka where enough food and roost- 1. A Serological survey conducted all over
ing place was available. Information was obtained India revealed a few samples from mature human
on the migrating routes of different species. Reco- individualsin an areaofSaurashtrahavingantibodies
very of a ringed bird or of its ring from distant to RSSE/KFD for which there appeared no
places gave further confirmation, and in some
explanation.
instances gave an indication of the life span of 2. The insect vector for RSSE is a mite,
the bird. The food sources and preferred roosting whereas for KFD the vector is a tick.
places, the associated climatic and environ- It may be postulated that at some time in the
mental conditions were all recorded and a large past a bird or birds infected with RSSE landed in
amount ofdata accumulated for future analysis and Saurashtra and shed infected mites, which in turn
study. infected some humans in the adjoining village. The
The initial camps were supervised by S£lim mites died out, unable to develop in the new
BNHS
Ali himself, with the assistance of the staff. surroundings, leaving as their only trace a few
As work expanded and more camps were set up, humans with antibodies to the disease.
some ofthese wererun by thenow well trained staff. What has happened once can happen again,
Several research workers and interested volunteers thenew scenebeing the KyasanurForest area. Here,
alsojoined the camps. In this process, the assistants though the mites died, the infection was taken up by
learned not only the techniques ofbird trapping and
ticks, possibly through theblood ofan infected bird
banding, but also received a thorough grounding in which lay dying on the forest floor. An arthropod
the techniques of careful and meticulous field borne virus is suited to one species of tick through
research. Some of S£lim Ali’s early assistants have which itistransmitted. Ifitentersthebody ofanother
gone on to become leaders in natural history field speciesiteitherdies outor itundergoes somechange
research within the country. Reports on these or modification which enables it to propagate itself
studies have been published in the Journal of the within the body ofthe new host. It may be assumed
BNHS.
that the virus ofRSSE entering the body ofthe tick
The virus problem: The virus of KFD was underwent such a modification to form the closely
identified and found to be similar but not identical allied virus of KFD. All this is speculation, but it
with that of RSSE. The trapped birds did not show appears to be the most plausible explanation which
the presence of infection, and when tested for
can fit the facts.
evidence of past infection, as shown by antibodies It is unfortunate that this sequence of events
in the blood, the results were negative or equivocal. resulted in a new disease. At the same time, it is
Reports of their findings are given in the published exciting to realize that we are privileged spectators
papers and the annual reports ofthe Virus Research of a small facet of the process of adaptation and
Centre (now renamed the National Institute of natural selection which forms thebasis ofevolution
Virology), Pune. oflife on the earth.