Rubber Tree Plantations And Dengue Fever

[timber]

Dengue Bulletin – Vol 27, 2003 197

Potential of Rubber Plantations as Breeding Source for

Aedes albopictus in Kerala, India

by

P K Sumodan#

Post Graduate Department of Zoology, Government College, Madappally, Vadakara-2, Kerala, India

# For correspondence: [email protected]

Introduction

Ever since the major outbreak of DF/DHF during 1996 in Delhi(1), dengue fever has

been receiving manifold attention from health authorities and researchers all over

India. For the first time, one imported dengue case was reported in Wayanad

district of Kerala and a death due to suspected dengue haemorrhagic fever in the

neighbouring Kannur district in June 2002. Vector surveys in localities associated with

these cases indicated that the dominant breeding site for Aedes albopictus, the

second most important dengue vector(2), was artificial containers used for collecting rubber

sap. During the south-western monsoon(June-September) season, it is a practice to

suspend tapping temporarily in some plantations leading to accumulation of

rainwater in these containers, thus providing ideal breeding sites for mosquitoes. Against

this backdrop a systematic study to substantiate the potential of rubber

plantations as sources for the proliferation of Aedes albopictus was conducted in three

villages each in Kannur and Wayanad districts from July to September 2002.

Kannur and Wayanad are two neighbouring districts in north Kerala.

Kannur district has 57,823 rubber plantations of different sizes occupying a total area of

33,944 hectares, while Wayanad has 10,244 rubber plantations occupying 6,450

hectares. The two districts receive on an average 300 mm of annual rainfall

Two categories of rubber plantations were selected for the study. They were

(i) with active tapping using rain guards; and(ii) where tapping was suspended with sapcollecting

containers intact but without rain guards. Ten plantations each were selected

under each category from both districts. In each plantation, 100 trees were surveyed at

random for mosquito breeding. Immature stages of mosquitoes were collected in

plastic containers and transported to the laboratory for emergence and identification

.

Potential of Rubber Plantations as Breeding Source for Aedes albopictus in Kerala, India

198 Dengue Bulletin – Vol 27, 2003

Results and discussions

In both districts the plantations with active rubber tapping, no sap-collecting containers

were found to be having rainwater. However, in the plantations where tapping

had been suspended, sap-collecting containers had rainwater collection and also

mosquito breeding (Table). In Kannur district, of the 1,000 trees surveyed, 802

(80.2%) had sap-collecting containers with rainwater. A total of 788 (98.3%) of these

containers were positive for Aedes albopictus breeding in association with other Aedine sp.

This species constituted 23.2% of the adult mosquitoes that emerged in the laboratory.

In Wayanad district, 917 out of 1,000 trees surveyed had sap-collecting containers with

water. However, only 807 (88.0%) supported mosquito breeding. Breeding of

Aedes albopictus was found only in 534(58.2%) containers. The percentage of Aedes

albopictus adults that emerged in the laboratory was 12.8%. On an average, each

hectare of rubber plantations had 330 trees. The capacity of a sap-collecting container was 500 ml.

This study emphatically indicates the potential of rubber plantations as important

sources for the proliferation of Aedes albopictus. In view of the fact that rubber

plantations play a significant role in the economy of the region, increased contact of

the human population with Aedes albopictus acquires greater epidemiological importance.

The study also revealed that those plantations where tapping was not

abandoned during the rainy season did not have any potential for mosquito breeding.

This is a positive aspect of the entire issue, as encouraging rubber tapping during the rainy

season using rain guards could be one of the most plausible solutions for the problem.

Acknowledgements

The author is thankful to the Director of Health Services, Kerala, for providing the

necessary facilities and to Mr CM Vinod, District Malaria Officer, Kannur, for his

assistance in carrying out the study. He is also grateful to the Rubber Board authorities

at Kottayam for providing facilities for the conduct of the study.

References

1. Anuradha S, Singh NP, Rizvi SN, Agarwal SK, Gur R

and Mathur MD. The 1996 outbreak of dengue

haemorrhagic fever in Delhi, India. South-East Asian

J Trop Med Public Health, 1998, 29(3): 503-506.

2. Shroyer DA. Aedes albopictus and arboviruses: A

concise review of the literature. J Am Mosq

Control Assoc, 1987, 2: 424-428.