The unbearable pain of a sting

CHENNAI: Mosquitoes are one of the biggest challenges to the public health sector across the globe. Despite decades of breeding prevention methods, that tiny insect has prevailed so well that mosquito-borne diseases are a major public health concern in India.

Dengue, Malaria, Chikungunya, Zika virus, Yellow Fever and many others are the most common mosquito-borne illnesses in the country and the diverse climate favours their growth.

The concepts of genetic modification, barrier-effects, mosquito nets, creams, lotions, and powders – none of it works. Public health experts emphasise on the need for focused research, public cooperation, field-level intervention and intensified public health measures to reduce the risk of mosquito-borne illnesses.

Entomologists urge the focus to be on sanitation and it doesn’t begin and end with sewage. Every household needs to take a step towards the prevention of mosquito-breeding. However, the focus on eradication intensifies only when mosquito-borne diseases increase and the public suffers on a large scale.

Less prevention methods

The need to control mosquito-breeding and to prevent diseases, especially dengue, arises mainly during September-November, every year. However, the ‘prevention is better than cure’ policy is not applied by the public or the stakeholders.

A study titled, ‘Knowledge and awareness towards dengue infection and its prevention: A cross-sectional study from rural areas of Tamil Nadu’, done in Kancheepuram and published in the International Journal of Community Medicine highlighted the same.

The study stated that though 93.7 per cent of people had heard about dengue infection, only 50 per cent of participants responded correctly to the symptoms of dengue and 89 per cent said that dengue is transmitted by the Aedes mosquito. However, only around 40per cent of the participants had knowledge about the breeding and biting habits of Aedes.

Vinoth Gnana Chellaiyan, department of community medicine, Chettinad Hospital & Research Institute, stated: “Though most participants had heard about dengue symptoms and the cause of infection, less than half were aware about breeding habits of Aedes, and 25 per cent did not follow any method of prevention. Community awareness plays key role in dengue prevention practices.”

In your homes

Tyres, tubes, refrigerator trays, coconut shells, old containers and plastic boxes are conventionally believed to be the breeding places for mosquitoes, which can also breed in just about 2 mm of depth of water. They can breed in any sort of container that has no direct contact with the soil.

John Victor, regional entomologist, State Health Department, said the source reduction was the key but in certain places where the source can’t be destroyed, insecticides are used to reduce breeding.

“If breeding is reduced, then adult mosquitoes will be less. Fogging is being done to kill them. Mosquitoes don’t travel for long and hence breed in households. To feed, it would just bite the people available around,” he explained.

Field inspectors have observed mosquitos occupy bathrooms with a cement container or drums meant for storage. “It’s important to change the water, so that the larva will be removed but the eggs are often in the inside walls. Hence, we ask the people to remove the water and clean the insides with bleaching powder. The terrace is a breeding ground as well as the tree leaves block the drain pipe and water stagnates in such places,” added Victor.

Environmental factors

A study titled, ‘Prevalence and trend of dengue via disease in Tamil Nadu during 2017-2021’, published by the Tamil Nadu Directorate of Public Health and Preventive Medicine, stated that a major proportion of positive cases were seen during post-monsoon period, prominently between September and November.

“Climate change is a vital factor that would have increased mosquito density resulting in expansion of the geographical and seasonal distribution of vectors,” the study observed. “The trend is that a major proportion of positive cases occur in the post-monsoon period. Thus, correlation between incidence of dengue infection and monsoon season is clearly evident and it has been also supported in previous studies from India and many parts of the world. The north and south regions of the State had major numbers and this could be probably due to varied climatic conditions apart from having coastal areas being suitable for vector breeding.”

Higher incidence of dengue cases was recorded in northern and southern zones of the State while the Central Tamil Nadu reported the least.

The study points out that dengue cases were reported nearly every month, but most were reported between August and December, and the spike was seen particularly in September and November. Among the northern districts, Tiruvallur and Cuddalore contributed more than 65 per cent of dengue cases.

The second highest number of cases was found in southern TN, especially in Ramanathapuram, Tenkasi, Tirunelveli and Virudhunagar, followed by western districts – Namakkal, Tiruppur and Erode. Dharmapuri was found to have the least number of cases. The top seven districts are Tiruvallur, Cuddalore, Ramanathapuram, Tenkasi, Namakkal, Tirupur and Tirunelveli, of which Tirunelveli had higher number of cases between February and May.

Quality control, funding

Disinfect, spray insecticides and undertake fogging to control the spread of mosquitoes – is the quality of the insecticide used in such measures optimum?

“We see the tenders being floated and of course, the lowest cost is accepted but we need to choose the quality disinfectant or chemicals to act on the breeding of mosquitoes. Funds to choose the best product for controlling the population of vectors is important. If the same product has been used for years and has not been effective, we must choose better alternatives,” said an entomologist with the State Health Department.

A microbiologist from the State Public Health Laboratory said that though there were various forms of insecticides, sprays and disinfectants being used, mosquitoes easily adapt with time. New interventions such as genetically-modified mosquitoes need a large-scale intervention in terms of funding for equipment and expertise.

“We’ve done studies on understanding the prevalence and risk factors. There has been some progress in the last decade or so but the progress to control breeding has been slow. Testing does not happen at the primary health centre level. We do not see a significant number of tests, as required for the population of large States like Tamil Nadu, until there is a major outbreak,” the microbiologist pointed out.

Natural parasites dip

Entomologists have observed that the increase in the population of mosquitoes over the years is said to have been because of the disruption in the ecosystem and the lack of natural parasites that have declined due to the pollution.

“Mosquito population is increasing because the pollution has increased exponentially over the years. DragonFly and DamselFly usually engulf the mosquito larvae but due to pollution, the population of these flies has reduced. There is a natural increase in the population of mosquitoes because of lack of potential parasites,” says E Mohan, regional manager-entomologist, in Nakasa Crop Science, Hyderabad.

He added that the process of egg-laying needs to be targeted so that the population can be reduced. “We cannot reduce the population of the mosquito immediately. We need a specialised team to monitor the whole life cycle of the mosquito and target the breeding. Chemical-based intervention needs to be introduced to reduce the risk of breeding in stagnant water. Egg-laying capacity of the mosquito needs to be targeted and appropriate research needs to be done in this regard. We don’t have adequate academic data in this regard,” stated Mohan.

More staff on the ground

Public health experts say that despite the policy-level intervention, the implementation at the grassroots level can be done only with the help of frontline workers.

“We do not have adequate staff on the field to conduct regular domestic-breeding checks. Every household needs to be inspected by health inspectors at least once a week. This practice was prevalent in the 1990s but over the years, the number of health inspectors has reduced in rural and urban areas,” recalled Dr K Kolandaisamy, former Director of Public Health and Preventive Medicine. “We have active ANM workers (Auxiliary Nurse Midwife) and Village Health Nurses in rural areas but we also need health inspectors to ensure the implementation of the methods in every household.”

He pointed out that the next step was to issue a penalty and fine on the people who do not follow instructions to clean their premises upon breeding checks. “Officials of the State Health Department have the authority to do the cleaning and maintenance of sanitation on their own if the commercial space owners or homeowners do not take action. They need to pay the charges for carrying out the cleanliness and hygiene activities,” he stated.

Focus on source reduction

In case of rain, and during water scarcity, the practice of water collection in households, construction sites, office spaces and hospitals are potential breeding points. Therefore, source reduction is very significant.

GCC Commissioner J Radhakrishnan said that the Aedes mosquito remains the biggest challenge because of storage mechanisms used in every household. “Source targeting needs to be done and the mosquito density needs to be controlled. But it’s not a single person’s responsibility and the cooperation of the people is important. We need a change of behaviour and it cannot be a blame-game,” he opined.

It’s a prevalent belief that drains and garbage cause mosquito breeding but the public must also check their homes and/or their surroundings where mosquitoes breed, causing dengue and chikungunya. “Even if an individual follows the preventive measures but their neighbours don’t, the threat of infection still remains. It’s a collective responsibility and the public needs to cooperate with the local bodies and State Health Department to ensure that mosquito breeding measures are effectively implemented,” he added.