India has seen a 6.2% increase in dengue cases in the last three years up to 2021 —- from more than 1.9 lakh cases in 2019 to over 2 lakh cases in 2021, as per Minister of State for Ministry of Health and Family Welfare, Dr Bharati Pawar's response in Rajya Sabha on August 2, 2022. On the other hand, Malaria cases dropped by 57% between 2019 and 2021, data from a Lok Sabha response given in February, 2022 show.

Vector-borne diseases such as Dengue, Malaria, Zika, Chikungunya and Lymphatic filiriasis are most common in India. While mosquitoes act as only one type of vector, aquatic snails, blackflies, fleas, lice, etc act as vectors for several other diseases.

These diseases are human illnesses caused by parasites, viruses and bacteria that are transmitted by vectors, according to the World Health Organization. These diseases account for more than 17% of all infectious diseases, causing over seven lakh deaths across the world annually.

Misinformation around common mosquito-borne illnesses are widespread. On World Mosquito Day, FactChecker spoke to Dr Umang Agrawal, Infectious Diseases Consultant, PD Hinduja Hospital and Medical Research, Centre, Mahim, Mumbai to help bust seven popular misconceptions surrounding mosquito-borne diseases.

Myth #1: A Person Can Get Dengue Only Once

Fact: There are four distinct strains of the dengue virus. Once a person is infected with one strain, their body will build up immunity to only that strain of the virus. This means that a person can get dengue another three times during their lifetime, according to the National Health Service UK. "A person can get dengue multiple times, however, for every new infection, the cause is a new strain," said Dr Agrawal.

Myth #2: Dengue is Contagious

Fact: Dengue cannot be spread by direct respiratory droplets or from person-to-person contact, said Dr Agrawal.

Dengue is spread through the bite of the female mosquito, Aedes aegypti. The mosquito becomes infected when it carries the blood of a person infected with the virus. Hence a person infected and suffering from dengue can infect other mosquitoes. According to the WHO, humans are known to carry the infection from one country to another during the stage when the virus circulates and reproduces in the blood system.

Myth #3: Mosquitoes that Spread Chikungunya and Dengue Breed Only in Dirty Water

Fact: Stagnant or still water breeds mosquito-borne diseases, said Dr Agrawal. Mosquitoes hatch eggs wherever they find stagnant water, including water-holding trays near plants, kitchens, buckets and mugs filled with water in bathrooms and toilets, etc.

The Aedes Aegypti mosquito that causes dengue is known to breed in clean stagnant water while the Anopheles and Culex mosquitoes breed in dirty water. According to the Centers for Disease Control and Prevention, different types of water attract different types of mosquitoes: Permanent water mosquitoes tend to lay their eggs in permanent-to-semi-permanent bodies of water. While some prefer clean water some like nutrient-rich waters, the CDC says.

On the other hand, Floodwater mosquitoes lay their eggs in moist soil or in vessels above the water line. These habitats include irrigated fields, containers that hold rainwater, temporary pools and ponds created by rain, etc.

Myth #4: Mosquitoes Prefer Certain Blood Types

Fact: This is absolutely wrong, Dr Agrawal said. Mosquitoes do not gravitate towards people with a particular blood type. Instead, they look to feed on protein which is found in blood. Blood consists of red blood cells, white blood cells and platelets in a liquid called plasma and a blood group is identified by antibodies and antigens in the blood.

Myth #5: Malaria Spreads Only During the Rainy Season

Fact: Plasmodium Vivax, one of the major causes of malaria. adapts to the dry season by developing a prolonged incubation stage in the human liver. This stage can remain dormant for almost nine months before multiplying rapidly in the blood during the infection stage, increasing the chances of a mosquito bite and transmission to a new host.

According to an October 2020 study published in Nature Medicine, researchers said, "Malaria parasites persist inside humans during the dry months at low levels that do not risk the host's health, guaranteeing their survival until the next wet season when parasite transmission can resume."

Myth #6: Chikungunya is a Fatal Illness

Fact: "Chikungunya is not a fatal illness unless it causes a respiratory compromise which is a possibility with any viral illness. The fatality rate of the disease in the country is low," said Dr Agrawal.

According to the CDC, death from Chikungunya is rare. While most patients feel better within a week, after effects such as joint pain might persist for a few months. People at risk for more severe disease include newborns infected around the time of birth, older adults (above 65 years), and people with medical conditions such as high blood pressure, diabetes, or heart disease.

Myth #7: The Birth Defects Associated with Zika are caused by Vaccines

Fact: The birth defects are caused by the virus itself, said Dr Agrawal. Misinformation regarding the vaccine causing birth defects was rampant during the Zika outbreak in Brazil in 2016. The Zika virus infection during pregnancy is known to cause Microcephaly (birth defect in which a baby's head is smaller than expected when compared to babies of the same sex and age) and other birth defects. Misinformation regarding the vaccine causing birth defects was rampant during the Zika outbreak in Brazil in 2016.

However, recognising that Zika is a cause of certain birth defects does not mean that every pregnant woman infected with Zika will have a baby with a birth defect, the CDC highlighted.

The CDC further said that as per available evidence, the Zika virus infection in a woman who is not pregnant will not pose a risk for birth defects in future pregnancies after the virus has been cleared from her blood.