Vector Borne Diseases



Vector borne diseases

Main vectors and diseases they transmit

• Vectors are living organisms that can transmit infectious diseases between humans or from animals to humans.
• Many of these vectors are bloodsucking insects, which ingest disease-producing microorganisms during a blood meal from an infected host (human or animal) and later inject it into a new host during their subsequent blood meal.
• Mosquitoes are the best known disease vector.
• Others include ticks, flies, sandflies, fleas, triatomine bugs and some freshwater aquatic snails.

Mosquitoes

1. Aedes

1. Chikungunya
2. Dengue fever
3. Lymphatic filariasis
4. Rift Valley fever
5. Yellow fever
6. Zika

2. Anopheles

1. Malaria
2. Lymphatic filariasis

3. Culex

1. Japanese encephalitis
2. Lymphatic filariasis
3. West Nile fever

Sandflies

1. Leishmaniasis
2. Sandfly fever (phelebotomus fever)

Ticks

1. Crimean-Congo haemorrhagic fever
2. Lyme disease
3. Relapsing fever (borreliosis)
4. Rickettsial diseases (spotted fever and Q fever)
5. Tick-borne encephalitis
6. Tularaemia

Triatomine bugs

1. Chagas disease (American trypanosomiasis)

Tsetse flies

1. Sleeping sickness (African trypanosomiasis)

Fleas

1. Plague (transmitted by fleas from rats to humans)
2. Rickettsiosis

Black flies

1. Onchocerciasis (river blindness)

Aquatic snails

1. Schistosomiasis (bilharziasis)

Lice

1. Typhus and louse-borne relapsing fever

Vector-borne diseases

 

• Vector-borne diseases are human illnesses caused by parasites, viruses and bacteria that are transmitted by mosquitoes, sandflies, triatomine bugs, blackflies, ticks, tsetse flies, mites, snails and lice.
• Every year there are more than 700 000 deaths from diseases such as malaria, dengue, schistosomiasis, human African trypanosomiasis, leishmaniasis, Chagas disease, yellow fever, Japanese encephalitis and onchocerciasis, globally.
• The major vector-borne diseases, together, account for aeround 17% of all infectious diseases.
• The burden of these diseases is highest in tropical and subtropical areas and they disproportionately affect the poorest populations.
• Since 2014, major outbreaks of dengue, malaria, chikungunya yellow fever and Zika have afflicted populations, claimed lives and overwhelmed health systems in many countries.
• Distribution of vector-borne diseases is determined by complex demographic, environmental and social factors.
• Global travel and trade, unplanned urbanization and environmental challenges such as climate change can impact on pathogen transmission, making transmission season longer or more intense or causing diseases to emerge in countries where they were previously unknown.
• Changes in agricultural practices due to variation in temperature and rainfall can affect the transmission of vector-borne diseases.
• The growth of urban slums, lacking reliable piped water or adequate solid waste management, can render large populations in towns and cities at risk of viral diseases spread by mosquitoes.
• Together, such factors influence the reach of vector populations and the transmission patterns of disease-causing pathogens.

Vector Borne Diseases in India

• There are many vector-borne diseases prevalent in India like malaria, filariasis, Kyasanur forest disease, Japanese encephalitis, scrub typhus, dengue and chikungunya.
• The control of all of them depends on an understanding of the natural cycles and epidemiology of their vectors.

Malaria

• Malaria is caused by a parasite called Plasmodium, which is transmitted via the bites of infected Female anopheles mosquito. In the human body, the parasites multiply in the liver, and then infect red blood cells.  
• Symptoms of malaria include fever, headache, and vomiting, and usually appear between 10 and 15 days after the mosquito bite. If not treated, malaria can quickly become life-threatening by disrupting the blood supply to vital organs.

Dengue

• Dengue fever, also known as breakbone fever, is a mosquito-borne tropical disease caused by the dengue virus. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles.
• Dengue is transmitted by several species of mosquito within the genus Aedes, principally A. aegypti.

Japanese Encephalitis (JE)

• JE is mostly present in in Southern India, Uttar Pradesh, North Eastern states, Haryana. Its causative agent  is Group B arbovirus (Flavivirus) & it is transmitted by Culex mosquitoes.

Chikungunya

• Chikungunya is a viral disease transmitted to humans by infected mosquitoes. It causes fever and severe joint pain.
• Other symptoms include muscle pain, headache, nausea, fatigue and rash.Joint pain is often debilitating and can vary in duration.
• The disease shares some clinical signs with dengue, and can be misdiagnosed in areas where dengue is common.

Filaria

• Filariasis  is a parasitic disease caused by an infection with roundworms of the Filarioidea type.
• These are spread by blood-feeding black flies and mosquitoes. This disease belongs to the group of diseases called helminthiasis.

Kala-Azar

• Visceral leishmaniasis also known as kala-azar, black fever is the most severe form of leishmaniasis.
• Leishmaniasis is a disease caused by protozoan parasites of the Leishmania genus. This disease is the second-largest parasitic killer in the world after malaria.

Kyasanur forest disease

• The Kyasanur forest disease, transmitted by ticks, and scrub typhus, transmitted by mites, are re-emerging in India.
• Birds and animals, both small and large and wild and domestic, are also involved in the transmission.

 

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