Dengue

Dengue Bulletin Volume 28 (2004)

 PDF Version

Short Note 2

Detection of Dengue Virus in Wild Caught Aedes albopictus (Skuse) around KozhikodeAirport, Malappuram District, Kerala, India

B.P. Das*, L. Kabilan**, S.N. Sharma*, S. Lal*, K. Regu*** and V.K. Saxena*

*National Institute of Communicable Diseases, 22 Sham Nath Marg, Delhi – 110 054, India

**Centre for Research in Medical Entomology, 4 Sarojini Street, Chinna Chokkikulam,

Madurai – 625 002, India

***National Institute of Communicable Diseases, Kozhikode Branch, Kerala, India

Introduction

In India, outbreaks of dengue fever (DF)/dengue haemorrhagic fever (DHF) have been reported in various parts of the country during the past four decades[1]. Aedes aegypti is the only vector that has so far been implicated in dengue transmission[1,2], even though Aedes albopictus is known to be present in some of the peri-urban and rural areas[2]. Recently, a survey was carried out in the Kozhikode (earlier known as Calicut) airport area of Malappuram district, Kerala. During 2002 and 2003 (up to July), 75 and 150 clinical dengue fever cases, respectively, were reported from the district[3]. Earlier, reports of Aedes survey in Kerala had shown the presence of Aedes albopictus in rubber plantation areas[4] and in plastic cups[5].

This communication presents the results of the detection of dengue virus from the wild and dry preserved, adult females of Aedes albopictus and their breeding indices in and around the airport area. The survey was carried out in May 2004.

Materials and methods

The Kozhikode airport is situated at 11˚.15' N latitude and 75˚.49' E longitude, in a hilly area of Malappuram district, Kerala. It became functional as an international airport in 1988. A larval survey was carried out in various types of water-holding containers to detect the breeding of Aedes (Stegomyia) mosquitoes, both inside the airport premises and its periphery up to about 600 metres. The larvae were identified as per the method described earlier[6,7]. Adults of Aedes (Stegomyia) mosquitoes were collected while landing on human baits by aspirator tube in a forested residential area about 600 metres away from the airport.

The wild Aedes albopictus females caught from outside the Kozhikode airport, the adults reared from larval collections from inside the Kozhikode airport and the city, and the adults of Aedes aegypti reared from larval collection from the Thiruvananthapuram international airport were separated sex-wise, pooled by species (about 15 adults per pool) and transported to the Centre for Research in Medical Entomology (CRME), Madurai, Tamil Nadu, in a dry state, for detection of dengue virus. The methodology followed was similar to that used for the detection of JE virus and based on the protocol developed and standardized by CRME[8]. However, the antibody (D3-5C9-1) was diluted at 1:5000 as being followed by CRME.

Results and discussion

Aedes survey

The survey for larval infestation in 52 houses/premises around the airport area revealed 16 premises as positive for Aedes albopictus breeding (house index 30.7%). A total of 272 wet containers searched for Aedes breeding revealed 41 containers as 

positive for Aedes albopictus and two for Aedes vittatus (container index 15.1% and 0.7% respectively). The most preferred containers for Aedes albopictus breeding were discarded tyres, coconut shells and plastic containers. The average landing rate of Aedes albopictus on humans was 20 females/human bait/hour.

Dengue virus detection in

Aedes albopictus

Of the three pools of Aedes albopictus tested for dengue virus infection following antigen-capture enzyme immunoassay (EIA), one pool was found positive for dengue virus (OD-0.32), thereby indicating dengue viral activity in this mosquito species. The mosquitoes in the positive mosquito pool were collected as landing collection around the Kozhikode airport on 28 May 2004, and transported as dry specimens to the CRME laboratory and processed on 8 June 2004 (Table). Earlier dengue virus was also isolated from Aedes albopictus collected in a village in Vellore district of Tamil Nadu[9].

Table. Aedes mosquito pools tested for dengue virus infection by ELISA

* Positive pool

The present study confirms that antigen-capture enzyme immunoassay is a useful surveillance tool for monitoring dengue virus infection in mosquitoes.

Acknowledgements

The provision of laboratory facilities and the permission for the study by the Director, Centre for Research in Medical Entomology, Madurai, Tamil Nadu, is gratefully acknowledged. The authors are thankful to Mrs V. Thenmozhi and Mr S. Venkatesan, CRME, for providing laboratory assistance.

References

1.      Yadava RL and Narasimham MVVL. Dengue/dengue hemorrhagic fever and its control in India. Dengue Newsletter, 1992, 17: 3-8.

2.      Das BP, Sharma SK and Datta KK. Prevalence of Aedes aegypti at the International port and airport, Kolkata (West Bengal), India. Dengue Bulletin, 2000, 24: 124-26.

3.      Anonymous. Annual Report of the Centre for Research in Medical Entomology, Indian Council of Medical Research, 2002-2003: 82.

4.      Sumodan PK. Potential of rubber plantation as breeding source for Aedes albopictus in Kerala, India. Dengue Bulletin, 2003, 27: 197-98.

5.      Hiriyan J, Tewari SC and Tyagi BK. Aedes albopictus (Skuse) breeding in plastic cups around tea-vendor spots in Ernakulam city, Kerala state, India. Dengue Bulletin, 2003, 27: 195-96.

6.      Das BP. A simple modified method for mounting mosquito larvae. J Commun Dis, 1986, 18: 63-64.

7.      Das BP and Kaul SM. Pictorial key to the common Indian species of Aedes(Stegomyia) mosquitoes. J Commun Dis, 1998, 30: 123-127.

8.      Tewari SC, Thenmozhi V, Rajendran R, Appavoo NC and Gajanana A. Detection of Japanese encephalitis virus antigen in desiccated mosquitoes: an improved surveillance system. Trans Roy Soc Trop Med Hyg, 1999, 93: 525-26.

9.      Tewari SC, Thenmozhi V, Katholi CR, Manavalan R, Munirathinam A and Gajanana A. Dengue vector prevalence and virus infection in a rural area in south India. Trop Med Int Health, 2004, 9(4): 499-507.