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National Institute of Communicable Diseases |
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ANNUAL REPORT 1997 |
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NICD Branch, Coonoor The
International Health Division of Rockfeller Foundation established a Malaria
Investigation Unit at Pasteur Institute. Coonoor in 1938 under the stalwartship
of Dr. F.Russel. Subsequently a field station was established at Mettupalaiyam,
Coimbatore district (T.N.) in the same year for undertaking laboratory and
field studies on the role of Anopheline species in Malaria transmission. In
1942 the Malaria Investigation Unit of Rockfeller Founation along with its
personnel and equipments was placed under the Malaria Institute of India and
thus establishing the Southern India Branch of the Institute. The Malaria
Institute in consonance with its scope and function was rechristened as
National Institute of Communicable Diseases (NICD) in July, 1963. Hence this
branch has derived its present name viz. NICD, Southern India branch, Coonoor. This
branch, along with its field station at Mettupalaiyam, undertakes research on
epidemiology and control of vectors of various communicable diseases which are
common in this region and also on the ecology and control of vectors of public
health importance. Main activities at the Branch Studies
on the field and domestic rodents in erstwhile plague endemic areas of Nilgiris
district, Tamil Nadu, Bacteriological investigations for the occurrence of Vibrio cholerae Non 01 among diarrhoeal
cases reporting to Government Hospitals of Coimbatore and Nilgiris districts
(T.N.). Studies
on the bioecology of mosquitoes in the Nilgiris and foot hill areas with
special reference to disease vectors. Survey
of ectoparasites among the rodents and domestic animals in the Nilgiris. Studies
on the role of Azolla plant in
controlling the mosquito breeding under field conditions at Wetland
Agricultural Farm, Coimbatore (T.N.). Screening
of filaria cases in selected towns of Coimbatore and Nilgiris districts (T.N.). Routine Services/Activities and maintenance of stock cultures of
various animals, pathogens and parasites: Cyclic
colonies of mosquitoes The
cyclic colonies of the following mosquitoes are being maintained at
Mettupalaiyam Field Station of this Branch. The specimens are being utilised
for various laboratory experiments, training/demonstrations to visitors and
also supplied to teaching/research institutions on demand. Anopheles stephensi (Salem strain) Culex quinquefasciatus (Mettupalaiyam strain) Anopheles stephensi (Coimbatore strain) Aedes aegypti (Kallar strain) Anopheles stephensi (Mettupalaiyam strain) Toxorhynchites splendens (Kallar strain) Maintenance
of larvivirus fishes The
stock of larvivorous fishes viz. Gambusia
affinis and Poeilia reticulata
are being maintained in the rock pools of Kurunthamalai and in cement tanks of
Mettupalaiyam Field Station. Maintenance
of Azolla Azolla
spp., the free floating aquatic fern, is also being maintained in cement tanks
of the Mettupalaiyam field station. Various studies are being carried out in
the laboratory to find out its utility on mosquito control. Research Projects 1. Studies on the Field and Domestic
Rodents in Erstwhile Plague Endemic Areas of Nilgiris District, Tamil Nadu A
research project has been initiated by NICD Southern India Branch, Coonoor in
collaboration with 5 rural plague control units viz. Naduvattam, Otacamund,
Kotagiri, Coonoor and Manjoor during 1992. A total of 407 rodents were trapped
during the period of January to December, 1997. Of the total rodents trapped
the species recorded in the order of abundance were Rattus rattus (378), Mus
musculus (23) and Bandicoota
bengaliensis (6). The ratio of wild and domestic rodents was 1 : 66.83.
During the study, a total of 36 fleas were recorded from the rodents received
from various units. Species identification revealed the occurrence of following
species viz. Xenopsylla cheopsis, X.
astia, Stivalius spp. The total flea index and specific flea index of X.cheopis were 1.24 and 1.10
respectively. 2. Bacteriological investigations for
the occurrence of Vibrio cholerae Non O1 among diarrhoeal cases reporting to
Government hospitals of Coimbatore and Nilgiris districts, Tamil Nadu Vibrio cholerae O139, a new serotype isolated
recently, is known to spread to various parts of the country. In order to find
out the occurrence of this strain in this region, a research project has been
initiated in this branch during August 1993. Stool samples/rectal swabs were
collected from the diarrhoeal cases reporting to various Government hospitals
of Coimbatore and Nilgiris. Only 21 cases were positive for oxidise test and
none of them showed positivity to V.cholerae
O139. Initially this project was being operated only in Coimbatore district.
During the year 1997, the study has been expanded to hospitals and Primary
Health Centres of the Nilgiri district also. Studies on the bioecology of mosquitoes in the Nilgiris and adjoining
Mettupalaiyam town with particular reference to disease vectors A
mosquito breeding survey was carried out in all the available breeding grounds.
Of the 5,164 habitats surveyed, 1,193 (23.10%) were showing positivity for
mosquito breeding. The altitude of a locality primarily govern vertical
distribution of mosquitoes. There is a clear reduction of mosquito breeding at
higher altitude while at foothills it was maximum. A total 23 of anopheline
species has been recorded from the study area which include many of the primary
vectors of malaria. The dengue vector mosquito was prevalent in the
Mettupalaiyam town and the larval indices were showing higher values. Due to
limitation of breeding habitats such as domestic wells, Aedes aegypti has even invaded uncommon breeding habitats such as
domestic wells. Further aspects of studies mosquito ecology and behaviour are
under progress. Studies on the role of Azilla plant in controlling the mosquito
breeding under field conditions at wetland Agricultural Farm, Coimbatore
(T.N.). The
symbiotic nitrogen fixing water fern Azolla
is used as an alternate or supplement source of nitrogen in rice fields. Since
it forms a dense mat on the water it acts as a mechanical barrier to the
ovipositing female mosquitoes. Field as well as laboratory studies carried out
in this regard in various countries showed its utility for control of rice field
breeding mosquitoes vectors. A study in this regard has been undertaken in
Tamil Nadu Agricultural University (TNAU), Coimbatore (T.N.). Paddy breeding
station and an adjoining Poongundram village in which the station is situated.
Adult mosquito collections were carried out in the village and monitoring of
mosquito immature breeding in experimental as well as control fields were also
conducted during the study period. A total of ten Anophelines and seven
culicines have been recorded during adult mosquito collection activities. The
impact of Azolla treatment on the
density of Anopheline and culicine mosquito breeding in rice fields was compard
between control and experimental fields at weekly intervals. During post
treatment period of Azolla (from 3rd
to 12th week after transplantation of rice plant) in the
experimental field the relative density of anopheline larval and pupal 36 and
54 percent and culicine larval and pupal showed a decline of 66 and 83 percent
reduction have been obtained than of control fields. Further replication of the
study in different paddy growing seasons and statistical analysis of the data
collected in this regard are under progress. In order to find out the effect of
Azolla plant on mosquito oviposition
laboratory trials were carried out in Mettupalaiyam Field Station. The
experiments were conducted with the cyclic laboratory mosquito colonies
maintained in the field station by using Barraud mosquito cloth cages of (30 x
30 x 30 cm). In each instance the freshly fed known numbers of the quinquafasciatus and Aedes aegypti were released in cages and
ovitraps (500 ml beaker) were also kept for oviposition with 2.5 gms, 5 gms,
and 10 gms fresh weight of Azolla
floated in 250 ml. of water. In each colony a cage control having only water were
also kept without Azolla. The
eggs/egg rafts were collected everyday and recorded. All the three mosquito
species studied exhibited reduction of oviposition in ovitraps with 10 gm. of Azolla. Since the higher quantity of Azolla form a dense mat over the water
surface ovitraps it resulted in reduction of number eggs/egg rafts laid by
these mosquitoes. Further aspects of the laboratory and field studies are under
study. |
