Fever Pitch

They8217;re all playing a role in your nearest municipality, but they will not be knocked out by a few puffs of insecticide. Experts agree fumigation is ineffective against the aedes8212;the carrier of dengue and chikungunya8212;as it knocks down a few adults at best, while a whole new generation breeds in less than a fortnight.

With no vaccine, medicine or technique available so far to tackle these diseases, the only strategy is vector control. The issue thus becomes a public health and sanitation issue rather than a medical one. And public health is the large gaping hole that makes this last-minute battle against the mosquito seem futile.

Fly by Night

India has a National Vector-Borne Disease Programme. Till date, of the entire range of viruses that mosquitoes carry, it focused only on malaria. That experience 8212; of studying the anopheles mosquito, the malaria-vector 8212; is of little consequence in dealing with the aedes mosquito, which behaves very differently from its long-feared counterpart.

As a result, Indian researchers face twin challenges: One, even as efforts to combat malaria are stepped up, some strains of the disease begin developing resistance and two, the dengue-carrying aedes requires a different strategy than the malarial anopheles.

According to experts, dengue is here to stay. 8220;It comes with urbanisation, better means of travel and the way water is used in urban areas,8217;8217; says P Jambulingam, deputy director at Vector Control Research Centre VCRC, Pondicherry. Different species breed differently: In water-scarce areas, people tend to store water8212;heaven for dengue aedes8212;while overhead tanks are perfect for the malarial variety and dirty, polluted ditches for the filarial variety.

Dengue is now endemic in more than 100 countries in Africa, the Americas, the eastern Mediterranean, the western Pacific and South-East Asia. The latter two regions are the most badly affected see report, In Flat Word8230;.

The World Health Organisation believes that two-fifths of the world8217;s population8212;some 2,500 million people8212; are at risk of the disease, and that there are 50 million dengue infections every year. Outbreaks have been reported almost every year since the first recorded episodes in Africa, Asia and North America in the late 18th century.

The only strategy that is practical and partially successful in several parts of the world is vector control.

All in the Implementation

The government of India says their three-pronged dengue prevention strategy is based on 8220;international experiences8221;. 8220;The WHO guidelines include all the international strategies,8221; says Dr P L Joshi, director, National Vector Borne Disease Control Programme.

According to Joshi, the policy, which was developed after a 2003 control-dengue directive from the Delhi High Court, includes three steps. First comes vector surveillance for both larvae and adults in basic sampling units like houses. The next step is vector management, including environmental management like improved water supply and mosquito-proofing of overhead tanks, reservoirs. Next comes chemical control with larvicide and inscecticide.

None of these steps are impossible, officials agree. 8220;We have everything but the problem is implementing the guidelines properly,8221; admits Joshi. 8220;Effective implementation is the key.8217;8217;

However, the guidelines are yet to travel from paper to performance. For instance, it is yet to be recognised that surveillance for disease-carrying mosquitoes is the most important step towards preventing dengue. 8220;A sampling technique is available. Based on that model, vulnerable areas can be mapped out. But local governments are not exercising that option,8221; says Jambulingam.

According to VCRC, it is not difficult to design an effective surveillance method. 8220;Ideally, there should be mapping based on environmental risk factors. The mosquitoes are known to come in cycles, once in every 3-4 years in a certain place after the rains. Once their presence has been detected, their density has to be determined. A sample has to be checked for presence of the virus. The actual cases of fever comprise the fourth and final stage.

8220;The shortcoming right now is that the government tends to get into the act after the first cases. Complete monitoring and early recognition is required before preventive measures can be taken,8217;8217; says Jambulingam.

Keeping a Watch

The malaria programme has had partial success largely because the implementation mechanism is in place. Every state is supposed to have a vector-borne disease control component; a coordinating system between the states and the Centre is also functional. Primary health centres carry out passive surveillance for malaria. There are 565 district malaria officers, 13,758 malaria clinics.

Yet even with malaria, no active surveillance is carried out. Already, strains of the anopheles mosquito are developing resistance to common pesticides. The AIIMS report, submitted to the health ministry on Friday, raises this very question: Are mosquitoes getting resistant to commonly used insecticides in the country? If so, it could well pave the way for vector-borne diseases in epidemic and endemic forms throughout the country, especially in the cities.

According to experts, though the aedes mosquito has not demonstrated any resistance to pesticides, the malaria carriers have.

According to Dr A P Dash, director, Malaria Research Centre, of the 58 species of anopheles mosquitoes, nine of the malaria-transmitting ones are showing resistance. 8220;In places like the North-East areas, in hilly areas and some areas in Gujarat, An.Culicifacies and An.Stephensi are showing resistance to commonly used insecticides like DDT, DHT. So we have to use other insecticides,8217;8217; he says.

The government says there is no epidemic, but it needs to act before it becomes one.

Blame it on the weather

Climate change, according to a WHO report, is fuelling vector-borne diseases like malaria, filaria and kala azar. It estimates that in 2000, two per cent of all malaria cases in the world occurred due to climate change.

Scientists have also documented the effect of climate change on the incidence of malaria in India. It is feared that in the coming years, climatic changes will take malaria to many parts of India where it is not yet prevalent, including the southern states and Jammu and Kashmir.

8220;Early last century, the river-irrigated Punjab region experienced periodic malaria epidemics,8221; says the report. 8220;Excessive monsoon rainfall and high humidity was identified early on as a major influence enhancing mosquito breeding and survival. Recent analyses have shown that the malaria epidemic risk increases around five-fold in the year after an El Nino event.8221;

According to the study, even small temperature changes can increase the prevalence of malaria.

8220;Globally, temperature increases of 2-3 degrees celsius would increase the number of people who, in climatic terms, are at risk of malaria by around 3-5 percent, that is several hundred million,8221; it says. The duration of malaria would also increase in areas where it is now endemic, the report says.