Viral threat from deforestation

NST: What have monkeys got to do with dengue? And what have dogs got to do with hookworm infection? Plenty, it appears, as TERESA YONG found out at a recent seminar on parasitology

KUALA LUMPUR: Much has been said about the environmental degradation caused by indiscriminate deforestation.
Chopping down trees, however, means much more than just that.
Everyone knows deforestation takes away the natural habitat of all kinds of jungle animals and drives them closer to human habitats.
What most do not know is that these animals put us at more risk from all kinds of diseases.
Studies done in 1986 suggest dengue viruses are maintained in a primate cycle involving monkeys and vectors of the aedes (Ae) niveus group.
This raises the possibility that the Ae albopictus mosquito may introduce the sylvatic (primate) virus to humans now that these primates live close to people in the urban areas, said Dr Indra Vythilingam, a research officer and former head of the Parasitology Unit, Institute of Medical Research.
Dengue is a viral disease that is transmitted to humans by two types of mosquitoes, Ae aegypti and Ae albopictus.
First reported in Malaysia in 1902, dengue affects 100 million people worldwide.
Dengue cases had more than doubled from 17,368 in 2001 to 39,654 in 2005. The fatality rate showed a similar trend over the same period, increasing from 50 to 107, according to Health Ministry statistics.
Malaysia has one of the best dengue control programmes in the region and yet cases of dengue fever and dengue haemorrhagic fever are increasing, said Dr Indra.
She presented a plenary paper on Emerging Threats of Vector-borne Diseases in Malaysia at the three-day 43rd Annual Scientific Seminar of Malaysian Society of Parasitology and Tropical Medicine and Centenary Celebration of The Royal Society of Tropical Medicine and Hygiene (UK) here recently.
She pointed out that a number of vector-borne diseases discovered decades ago still persist now. These diseases include malaria, dengue, filariasis and Japanese encephalitis.
Some have become of greater public health importance now than before.
"Dengue is a good example of one that is increasing in the number of cases over the years. It has acquired a higher status since it poses a great threat to the people in urban areas."
Chikungunya, another viral disease, is also resurfacing in Malaysia and the main vectors are the same for dengue. Two outbreaks were reported in Klang in 1998 and last year in Bagan Panchor, Perak.
Malaria, which kills a child every second in Africa, is well under control in Malaysia.
"However, our neighbouring countries are not so fortunate and malaria is a serious problem there. Now, due to good diagnostic techniques, we are seeing simian malaria in humans.
"Perhaps this could lead in the future to simian malaria being transmitted from humans to humans," she warned.
Of the parasitic vector-borne diseases, filariasis is rare in Malaysia. However, of late, an increasing number of cases of Wuchereria bancrofti (which causes elephantiasis) are being imported into the country.
Culex mosquitoes, the main vector, is abundant and they are susceptible to the parasite.
Dr Indra said there was too much emphasis on fogging to kill adult mosquitoes. Instead, she said, the breeding sites should be eliminated.
Dr Indra said the health system must be strengthened so that health workers can provide effective intervention and assess the success in controlling the vector-borne diseases.
Besides deforestation, other factors which increase the risk of vector-borne disease transmission include natural disasters and poorly planned urbanisation which leads to the mushrooming of settlements with poor water supply.
Environmental changes and rapid air travel also directly affect the emergence and resurgence of such diseases, said Dr Indra.