Kiyoshi Kamimura ( Department of Pathology, Toyamain Medical and Pharmaceutical University, Sugitani, Toyama 930-01, Japan. )
Toshiaki Takasu ( Department of Neurology, Nihon University School of Medicine Itabashi, Tokyo 173, Japan. )
Altaf Ahmed ( Department of Health, Karachi Metropolitan Corporation (KMC), Karachi, Pakistan. )
Akhtar Ahmed ( Department of Neurology, Dow Medical College, Civil Hospital, Karachi,Pakistan. )
A survey was conducted to determine the number and the species of mosquitoes which transmit diseases in Karachi with special reference to possible vector of Japanese encephalitis virus-Culex tritaeniorhynchus. This species has been found throughout Karachi. Four other species mosquitoes were also identified. With detection of 5 serological probable cases of JE in the larger study, the next question of an animal reservoir has arisen. (JPMA 36: 182, 1986).
Fauna of mosquitoes in Pakistan was first published by Aslam Khan1. He listed 92 species, but only a few from Karachi area. The first mosquito species recorded from Karachi city was Aedes aegypti by Barraud2. Later Anopheles stephensi3,4 Culex tritaeniorhynchus5 and An. subpictus6. were detected in this city.
In 1983 the field study team of encephalitis in Karachi area sponsored by the Japanese Ministry of Education and Science surveyed the area widely and found five common species of mosquitoes. This report is the result of the survey.
MATERIALS AND METHODS
Studies were conducted in 22 localities evenly distributed throughout in Karachi city (Fig. 1).
Adult mosquitoes were collected mostly by spray sheet collections and sometimes hand collections from the resting sites of mosquitoes. In addition to these, mosquitoes were also collected from cattle sheds at night. For the spray sheet collection, white sheets were laid over the entire floor and beds in the room, all doors and windows were closed and pyrethrum in Kerosene was sprayed. After about 10 minutes killed adult mosquitoes were collected from the sheets. To detect larvae, dips of water were examined at each breeding place in the same localities which are mostly adjacent to tributaries of Lyari river into which sewerage is discharged.
By spray sheet collection in Karachi area, 12636 female and 7,952 male mosquitoes were identified.
Table 1 (upperside) and
Figure 2 indicate the number of adult mosquitoes captured at Azam town, near seaside of Karachi city. Cx tritaeniorhynchus, the principal vector of J. encephalitis and west nile (WN) virus and Cx. quinquaefasciatus were abundant in the summer season from July to August, and their common breeding places were ground pools at the riverside of tributaries of Lyari river.
Table 1 underside and Figure 3 indicate the number of adult mosquitoes captured at Cattle colony Malir, Karachi. Cx. pipiens quinquaefasciatus, the principal vector of filariasis appeared in all seasons, and their common breeding places were cesspools and ditches in human habitation. An. stephensi, the principal vector of malaria, were rare. An. subpictus were abundant from July to October, and their common breeding places were ground pools, cesspools and ditches in the human habitation and along riversides.
The number of adult mosquitoes captured at the other localities in Karachi city. Ae. aegypti, the principal vector of dengue, was abundant in the sunijner season from July to September at the midtown area and their common breeding places were water tanks. Cx. tritaeniorhynchus was rare (Table II).
Table III indicates the number of adult mosquitoes captured in the bedrooms of nine encephalitis patients. Number of resting mosquitoes were fewer than those on the riverside. Cx. tritaeniorhynchus (abundant in the outskirts and the riverside of Karachi area) were fewer in the houses of encephalitis patients.
Table IV shows the number of adult mosquitoes captured at the outskirts from Thatta to Hyderabad. Cx. tritaeniorhynchus were breeding abundantly in the rice fields, swamps and ground pools.
The species and the number of mosquitoes which carry viruses were surveyed in Karachi area, Pakistan. Cules tritaeniorhynchus, which cany Japanese encephalitis virus, were distributed all over Karachi area in low density. Anopheles step. hensi, vector of malaria, were rare but An. subpictus were abundant. Cx. pipiens quinquae fasciatus, vector of fuiariasis, had appeared throughout the season and Aedes aegypti, vector of dengue appeared in the town in rainy season.
It has been debated whether Japanese encephalitis occurs west of India. In this Project studies five suspected cases of Japanese encephalitis were found (Taksau et al7). In Karachi area great many cattles are reared but not pigs, the known carriers of Japanese encephalitis, and also the density of Cx. tritaeniorhynchus, the principal vector of Japanese encephalitis, was low. So perhaps some of these cattles get infected with Japanese encephalitis virus and act as reservoirs. On the other hand if the vector mosquitoes of Japanese encephalitis were to appear abundantly, most of the animals would develop anti-body and the Japanese encephalitis virus would not be able to maintain itself and new infection with Japanese encephalitis would not be found. Pigs, ‘amplifiers’ of Japanese encephalitis virus, are not reared in Karachi area. In the outskirts from Thatta to Hyderabad, Cx. tritaeniorhynchus breed abundantly, the wide pigs for which the area is well known may provide the reservoir for the IE virus. This aspect needs to be investigated further.
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2. Bariaud, P. J. The fauna of British India, including Ceylon and Burma. Diptera Vol. 5. Family Culicldae; Tribes Megarhini and Culicim. London, 1934; P. 463.
3. Talibi, S.A. and Hussain, M.Z.Y. Incrimination of the vector of malaria in federal Karachi area (Pakistan) Pakistan J. Hith., 1958;665.
4. Afridi, M.K., Talibi, S.A., Rashid, S.A. and Husain, M.Z.Y. Identification of races of anapheles A. stephensi prevalent in the federal Karachi area by measurement of their ova. Pakistan J. HIth., 1958; 8:71.
5. Baker, R.H. and Aslamkhan, M. Mutants of Culex tritaeniorhynchus Giles, 1968; WHO/VBC, 68. 84. 4pp.
6. Aslam Khan, M. and Baker, R.H. Karyotypes of some anopheles, ficalbia, and culex mosquitoes of Asia.Pakistan J. Zool., 1969; 1:1.
7. Takasu, T., Ahmad, A., Kono, R., Kondo, K., Aoyama, Y., Sugamata, M., Chida, K. and Kamel, S. Neuro-virological research of encephalitides in and around Karachi; the clinical aspects (interim report). JPMA.,1986; 36:159.