Mosquito-Borne Diseases

Introduction

Mosquito-borne disease is an illness of humans caused by the bite of a female mosquito during its blood meal. Mosquitoes get infested with pathogens like viruses and parasites while feeding on the blood of infected birds or mammals and act as vectors for disease transmission. Disease symptoms are usually asymptomatic at the initial stage, but in mild conditions, there is fever, body aches, joint pain, headache, and rashes, while chronic situations can lead to high fever, stiff neck, coma, seizures, bleeding, brain inflammation, and paralysis.

Common Mosquito-Borne Diseases

Lymphatic filariasis

Lymphatic filariasis is commonly known as elephantiasis. It is a neglected tropical disease and is transferred inside human body through bite of female Anopheles mosquito. Three types of filarial roundworms are common - Wuchereria bancrofti, Brugia malayi, and Brugia timori.

Microfilariae are transmitted to mosquitoes by biting an infected person. These parasites mature into infective larvae within mosquito and on biting a healthy person are deposited on the skin, which then migrates into lymphatic vessels and develops into adult worms.

Clinical symptoms in chronic disease include lymphoedema or tissue swelling, elephantiasis of limbs and hydrocele, swelling of scrotum, breast, and genital organs. In the last two years, 860 million people in about 50 countries were reported to undergo treatment for elephantiasis.

Malaria

Malaria is caused by a protozoan parasite -Plasmodium. Five Plasmodium species cause malaria in humans- Plasmodium falciparum and P. vivax are the deadliest, other species are P. ovale, P. malariae, and P. knowlesi. Inside human body, the Plasmodium invade the red blood cells and continue its life cycle, reach the peripheral blood vessels, and transmitted inside mosquito body. Inside the mosquito body the parasite completes its life cycle and reaches the infective stage. It can also be transmitted through blood transfusion, organ transplants, use of shared needles, mother to foetus during delivery.

Clinical symptoms of malaria include fever, headache, chills, muscle pain, cough, vomiting, diarrhoea, and abdominal pain.

The latest World Malaria report shows 247 million malaria cases in last two years and an estimated death of 6,19,000 people worldwide. The African region is reported to carry the highest share of global malaria burden about 95% of all cases and 96% of mortality reports.

Japanese encephalitis

Japanese encephalitis is caused due to inflammation of the brain by Japanese encephalitis virus (JEV), a flavivirus, transmitted by female Culex mosquitoes. Mosquitoes get infested with the virus while feeding on pigs and wild birds which are later transmitted to a human host while feeding on their blood. It can also be transmitted by blood transfusion or organ transplant. The disease is predominantly evident in rural and suburban regions, where humans live in vicinity of domestic animals.

Clinical symptoms in children cause gastrointestinal pain and vomiting, mild infections include fever and headache, and in more severe infections rapid occurrence of headaches, high fever, impairment of mental condition, neck stiffness, coma, convulsions, tremors, and paralysis. JEV infections are usually mild, case fatality can be 30% among people with symptoms.

West Nile fever

West Nile fever is caused by the West Nile virus (WNV), a neurological disease, most common in Africa, Middle East, Europe, West Asia, and North America. WNV is a flavivirus and humans are infected by the bite of female Culex mosquito.

Mosquitoes get infested with the pathogen while feeding on infected birds, virus develops inside mosquito body and infective stages reach their salivary glands. Later, during blood meals from a mammalian host, virus gets transferred into the animal body, it multiplies and causes illness. In rare cases, transmission can occur through organ transplants, blood transfusion, and feeding on breast milk.

Clinical symptoms are high fever, headache, neck stiffness, muscle weakness, coma, convulsions, tremors, stupor, and paralysis.

Chikungunya

Chikungunya is caused by chikungunya virus (CHIKV), an RNA virus, and transmitted by female Aedes mosquito. The name Chikungunya is in Kimakonde language, meaning - ‘to become contorted.’ When a mosquito feeds on blood of a CHIKV infected person, they ingest the virus and it then replicates inside the mosquito, matures, and reaches its salivary glands. On biting a healthy person, the pathogen is transmitted, the virus completes its life cycle and causes illness.

Clinical symptoms are fever, muscle and joint pain, headache, swelling of joints, skin rashes, and fatigue.

Dengue fever

Dengue or breakbone fever is caused by Dengue virus (DENV) and transmitted by female Aedes mosquito. It is common in tropical and subtropical regions. The pathogen is transmitted from an infected person when a mosquito feeds on their blood. DENV replicates inside mosquito body and the infective stage reaches the salivary gland which is transferred to a healthy person on biting.

Pathogen transmission can also occur from mother to foetus, organ transplants, and blood transfusion. Dengue fever is endemic in the regions of Americas, Africa, Eastern Mediterranean, Western Pacific, and South-East Asia. Asia reports around 70% of global disease burden.

Clinical symptoms include high fever, headaches, muscle and joint pain, nausea and vomiting, skin rashes, and swollen lymph nodes.

Rift Valley Fever

Rift Valley fever (RVF) is a viral zoonotic disease, that primarily affects animals, but can also affect humans. Human infections can occur while handling animal tissues in slaughters, animal births, veterinary hospitals, or animal carcasses and foetuses. People of occupations like slaughterhouse workers, veterinarians, farmers, and herders are prone to such diseases.

Transmission of pathogen can also occur from the bites of female Culex and Aedes mosquito.

Clinical symptoms in mild conditions include fever, muscle and joint pain, headache, sometimes neck stiffness, vomiting, loss of appetite, and sensitivity to light.

Yellow fever

Yellow fever, a viral haemorrhagic disease, is caused by yellow fever virus, a flavivirus, and transmitted by female Aedes mosquito. ‘Yellow’ name is significant for the occurrence of jaundice in some people. The disease is endemic to Africa and Central and South America. The disease pathogens are transmitted from an infected person on bite of the mosquito and transmission to another healthy person on biting.

Clinical symptoms include high fever, headache, backaches, nausea or vomiting, loss of appetite, abdominal pain, jaundice, and internal bleeding.

Zika

Zika is caused by Zika virus and transmitted by female Aedes mosquito. It is most common in tropical and subtropical regions. Transmission occurs by a mosquito biting an infected human, virus replication and biting a healthy human. It can also be transmitted from an infected mother during pregnancy to her child and result in serious health anomalies like microcephaly, sexual contact, blood transfusion, and organ transplantation. Most people with Zika virus are asymptomatic.

In severe cases, clinical symptoms include fever, muscle and joint pain, red eyes, headache, and skin rashes.

FAQs

Qns 1. Are mosquito-borne diseases common?

Ans. Yes.

Qns 2. Are these diseases transmittable?

Ans. Yes, through the bite of mosquitoes only.

Qns 3. Can mosquitoes spread more than one disease?

Ans. Yes, one mosquito can spread many diseases.

Qns 4. Are these diseases curable?

Ans. Yes, depends on the stage of infection.

Qns 5. Are there vaccines?

Ans. Yes, in some cases vaccines are effective.