Going beyond research to help us stay ahead of the dreaded mosquito

More than new research, better monitoring of vector-borne diseases and a safer environment are what can help us stay ahead of the mosquito, writes Ritwik Sharma

It’s that time of the year. Across much of India, the monsoon rains have brought respite from the blazing summer months. And just as inevitably, the mosquito and its sting is following it up like a party pooper. Fever accompanied by chills, joint and muscle pain, rashes et al are all too common symptoms as every second person contracts one or the other mosquito-borne disease.

The threat of these ailments refuses to die down, despite a decline in malaria cases that has enthused the Indian government to set a target of eliminating the disease by 2030. In recent years, dengue has witnessed a rising trend.

According to the World Malaria Report 2018, India recorded a 24 per cent decrease in its disease burden between 2016 and 2017. India is the one among the 11 nations with 70 per cent of the world’s burden of malaria to have registered a decline, and it managed to exit the position of the top three nations with the highest incidence. The report, however, noted that malaria still posed a risk to 94 per cent of India’s population. More than 200 million new cases of malaria are reported annually, says the World Health Organization, while the estimated number of deaths resulting from it stood at 435,000 in 2017.

Ramesh C Dhiman, senior consultant and former scientist at the Delhi-headquartered DST-ICMR Centre of Excellence on Climate Change & Vector-Borne Diseases, Indian Council of Medical Research (ICMR)-National Institute of Malaria Research, says that the reasons for decline in malaria cases of late are strengthened intervention measures – rapid diagnosis in inaccessible areas, radical treatment and better coverage by long-lasting insecticidal nets. “There is no scare. However, if the intervention measures are relaxed, resurgence may be expected as we are not reducing the vectors’ density,” he adds.

Dengue, which is not curable unlike malaria, is the fastest growing mosquito-borne disease globally and it hits nearly 400 million victims every year. In India, nearly 100,000 cases and 220 deaths were reported in 2015. In 2017, dengue cases were reported to be highest (188,401) in the country in a decade, with 325 deaths.

The World Mosquito Program (WMP), a not-for-profit initiative that works to protect the global community from mosquito-borne diseases such as Zika, dengue, chikungunya and yellow fever, points out that more than 40 per cent of the world’s population, in more than 100 countries, is at risk of dengue infection. The most significant epidemics in recent years have occurred in Southeast Asia, the Americas and the Western Pacific. Annually, around 500,000 cases develop into dengue haemorrhagic fever, a dreaded form of the disease – the virus has four serotypes or variations – resulting in the deaths of nearly 25,000 people worldwide.

In India, work on application of a safe and natural bacteria called Wolbachia for control of mosquito vectors of dengue and chikungunya is underway at the Vector Control Research Centre in Puducherry. In 2017, ICMR inked an MoU with Monash University, Australia, for this purpose. The WMP, pioneered by Australian researchers, has taken the Wolbachia method to 12 countries including India. In this formula, Wolbachia is introduced to the Aedes aegypti mosquito, which carries the dengue, chikungunya and Zika viruses. Once the Wolbachia-carrying mosquitoes are freed from labs, they breed with wild mosquitoes. Eventually, a majority of the vectors carry Wolbachia with less ability to transmit the harmful viruses, thereby limiting chances of outbreaks.

ICMR researchers have developed what they call the Puducherry variant and are rearing the mosquitoes in the lab to be released into the open during field trials by the end of next month, The Indian Express reported.

A recent article, titled “Estimating the dengue burden in India”, published in The Lancet Global Health says that quantifying the true burden of dengue globally remains “elusive because surveillance systems are notoriously poor at capturing all symptomatic dengue infections, resulting in gross under-reporting”.

Surveillance is the major issue when it comes to determining the actual number of cases of any vector-borne disease, agrees Dhiman. “Say for malaria, a mechanism has to be evolved to incorporate the cases treated by private medical practitioners. In the wake of the malaria elimination goal by 2030, adequate manpower for surveillance, particularly in inaccessible areas, is required. Health-seeking behaviour of communities for timely diagnosis and complete treatment should be improved by constant health education.”

Dengue and chikungunya, which require similar supportive treatment, can be controlled by effective health education, he adds.

Poor environments in cities are also to blame for the outbreak of diseases such as dengue, which have spread from urban centres to towns and villages. So it is not a surprise to find patients thronging dengue wards at hospitals in a city like Delhi, despite routine measures by the administration such as fogging.

Yogesh Jain, one of the founders of Jan Swasthya Sahyog, a not-for-profit that provides health care in Chhattisgarh, says that our urban infrastructure leaves us with no hope of preventing outbreaks in the future.

“If there is water stagnating in cities, you cannot stop mosquitoes from breeding. If you have population density of 5,000 in less than a square km, the impact will be magnified,” he says, adding that is why the worst outbreaks of dengue in Delhi spread from hospital campuses.

“Is it any consolation as a human being if one dies of dengue rather than malaria? That is what is happening.”

More than new research findings and knowledge, Jain says, we need to ensure appropriate methods are in place to diagnose people in a timely manner. The personnel involved in public health surveillance also should not be taken to task for the incidence of diseases.
 

SMALL STEPS, BIG GAIN
 
The prevention of mosquito-borne diseases, mainly dengue and chikungunya that have no cure, needs proper management of the environment.
 
One scientist advises individuals and communities to prevent stagnation of water around houses and well-fitting covers on tanks to prevent breeding of Anopheles (malaria vector) or Aedes mosquitoes. At construction sites, similarly, the concrete testing equipment should not have water after completion of work, and pits should be levelled. Garbage disposal is also crucial to curb breeding of the Aedes mosquitoes, the vector of dengue and chikungunya.
 
Water stored in cement tanks or other containers should be emptied or used within five-six days. To avoid mosquito bites altogether, one should apply repellents on exposed parts of the body while venturing out, especially in the evening. Mosquito nets may also be used.

“The approach where people who are supposed to do surveillance are also supposed to be the service provider is counterproductive. Every year we hear of people who will deny there is malaria or dengue in an area, and by the time the epidemic gets magnified, you can do very little to remedy that.”

Malaria is caused by Plasmodium. Humans are infected by four different species of the protozoan parasite — P falciparum, P malariae, P ovale and P vivax. The falciparum malaria, which is the most severe form, hits the poorest sections such as tribals and forest dwellers, while the less harmful vivax malaria strikes mostly in urban areas.

When it comes to drug development, too, the suggestion is better management of the ones already at our disposal — a factor that can be critical in thwarting possible resurgence of malaria amid the optimism of recent years. Already, reports by researchers have suggested drugs are failing at a sharp rate in Southeast Asia due to drug-resistant strains of malaria.

In the Mekong Delta, especially, resistance to artesunate (medication to treat malaria) has been reported raising fears of the parasite spreading to India and elsewhere. In the Northeast, which is not far from the region, cases of drug resistance has been documented earlier.

“We have no other drugs if artesunate stops working,” cautions Jain, adding that it should be prescribed for full treatment of a patient and not merely till relief from the symptoms.

Even as diseases such as malaria and dengue, or more recently Zika virus, dominate the public discourse, other vector-borne diseases such as scrub typhus — caused by infected larval mites — lurk in the horizon.

“Doxycycline, the drug used for its management, is one of the cheapest antibiotics that we have. Usually, expensive antibiotics such as linezolid and cephalosporin that are given to patients in city hospitals don’t work in this infection. So, people have to be educated and trained in the way we use our antibiotics,” says Jain.