Distribution of mosquito borne illness in India

The most prevalent mosquito-borne diseases occurring in India are malaria, dengue fever, and chikungunya. Though distributions and severity of each disease vary considerably. It is worth noting that despite high concentrations of each disease in specific regions, due to rainy seasons mosquitos are capable of spreading across the vast majority of India, with only a few millimetres of stagnant water serving as a potential breeding area.

Malaria

Malaria is transmitted in India by a species of mosquito of the same genus as in Africa, Anopheles. Though various species within the genus are capable of harbouring the disease, in all cases it is carried by an infected female. Though there are overlaps of areas with disease outbreaks, malaria is not as prominent in the south of India as dengue or chikungunya due to the varying species of mosquito carrying the disease.

The disease itself is caused by single celled protozoan called Plasmodium malariae. Symptoms include fever, vomiting and fatigue, though more serious cases can lead to coma and potentially be fatal.

The mosquitos are prominent in tropical, or subtropical regions, and so are commonly found in the north-east region of India (the “seven sister states” as well as Bihar, West Bengal, Jharkhand, Odisha and Sikkim) where damp conditions are perfectly suited for breeding habitats. The mosquitos are also found in urban areas where water tanks and areas of pooled stagnant water allow for ample breeding grounds.

Dengue fever

Unlike Malaria, dengue fever is spread via the Aedis aegypti species of mosquito. This species flourishes more prominently in the south of India but is also at a high concentration in the north-east, again due to wet, forested habitats that are ideal mosquito breeding conditions. This however does not mean the disease is isolated to these regions, with reports of dengue outbreaks this month as far to the north-west as Ahmedabad despite temperature drops. Major cities such as New Delhi are also experiencing outbreaks despite falling temperatures.

The disease is caused by the Dengue virus, with symptoms ranging from the characteristic skin rash to fevers, headaches, vomiting and muscle pain. There is the possibility that further issues may occur due to the disease, with two further conditions being Dengue hemorrhagic fever, in which a reduction in blood platelets, coupled with blood plasma leakage and bleeding can lead to fatality. The other being Dengue shock syndrome, in which severe low blood pressure occurs that can lead to loss of consciousness and potentially death.

Contrary to the spread of the disease in 2015, in which dengue outbreaks were largely confined to the south, the states with the highest count of deaths caused by dengue fever this year were for the most part in the north.

Chikungunya

Spread primarily by the same species of mosquito as dengue fever, typically showing a higher infection rate in the southern states. Much like dengue fever chikungunya has seen a surge in northern states this year, not seen since the last large outbreak of the disease in 2016.

The chikungunya virus is typically not fatal, though can cause death in those with pre-existing health conditions as the symptoms can be debilitating. These symptoms include: fever, joint pain, muscle pain and rashes. While not as serious a condition as dengue fever or malaria, no treatment for chikungunya currently exists. This in itself can cause issues as an outbreak in an unprepared area can lead to hospitals being overwhelmed.

Japanese Encephalitis

Transmitted by mosquitos of the Culex genus, Japanese encephalitis is caused by the namesake virus of the Flaviviridae family. Though the disease is transmitted by mosquitoes it is harboured by both livestock and some species of wild bird, resulting in it being far more common in rural areas.

In India the disease is most common in the following states: Andhra Pradesh, Assam, Bihar, Goa, Haryana, Karnataka, Kerala, Tamil Nadu, Uttar Pradesh and West Bengal.

While the disease is mostly asymptomatic, concern arises due to potential long lasting neurological damage in a minority of cases. Mild cases may come with a headache or aseptic meningitis, whereas severe cases can show a rapid onset with high fever and the possibility of permanent neurological damage.

(Following a recent article published to Health Issues India (HII) regarding mosquito-borne disease, an in depth look at some of the more common diseases may help to provide a better understanding of the issue.)