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Understanding Vector-Borne Diseases: A Quick Overview

VECTORS ARE SMALL ORGANISMS THAT CARRY SERIOUS INFECTIONS!


Vector-borne diseases share 17% of all the infectious diseases globally and lead to 7,00,000 deaths annually. These are the diseases caused by bacteria, viruses and parasites which are transmitted through certain vectors which acquire the organisms while biting the host during their meal and pass on to other hosts subsequently during their next meal. The common vectors include mosquitoes, ticks, fleas, sandflies, snails, etc. These diseases cause chronic suffering, life-long morbidity, disability, high mortality rates with a potential risk for outbreaks. The most prevalent vector-borne diseases are malaria, dengue, schistosomiasis, human African trypanosomiasis, leishmaniasis, yellow fever, Japanese encephalitis, chikungunya, zika, lyme disease. Malaria has been the deadliest vector-borne disease with 219 million cases globally. Dengue has been estimated to have 96 million symptomatic cases and an estimated 40,000 deaths every year. Vector-borne diseases occur at different regions but affect the lower socio-economic groups more rapidly. These diseases can be deadly and need to be prevented to decrease the morbidity and mortality by vector control measures personally and community based by the government.  


Keywords: Vector-borne diseases, insects, mosquito, malaria, dengue.



Have you ever been bitten by a mosquito, tick, or a flea?

Many of us have been bitten by either a mosquito, tick, or a flea at least once in our lives. Some of these insect bites can be a way for the bacteria, parasites, or viruses to enter the body and cause what are known as vector-borne diseases. WHO estimated that of all the infectious diseases, vector-borne diseases account for about 17% and cause 7,00,000 deaths every year. Some diseases have been for more than a thousand years like plague, and some have been discovered recently. Malaria has been accounted for as the deadliest vector-borne disease. [1]




Vectors:

There are different types of species which act as vectors in transmitting diseases from animals to humans or humans to humans. These vectors are usually bloodsucking arthropods which acquire disease-causing organisms when they bite the infected host for a meal and then transmit into new host during subsequent bite, and the cycle being repeated. The most common vectors are mosquitoes, ticks, fleas, snails, blackflies, lice, sandflies, and tsetse flies. [1]


Common vector-borne diseases:

The most prevalent vector-borne diseases are malaria, dengue, schistosomiasis, human African trypanosomiasis, leishmaniasis, yellow fever, Japanese encephalitis, chikungunya, zika, Lyme disease, and onchocerciasis. A vast number of these diseases occur in tropical and sub-tropical areas affecting the poor population. Some of these have caused chronic suffering, life-long morbidity, and disability. There have been many epidemics and endemics which have claimed so many lives. The common vector-borne diseases in tropical and sub-tropical regions are Malaria, Dengue, Filariasis, Leishmaniasis, Japanese encephalitis and Chikungunya. [1] [2]


MALARIA:

Malaria is a life-threatening parasitic disease caused by parasites known as Plasmodium vivax, Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale with over 219 million cases globally and results in more than 400,000 deaths every year. Most of the deaths occur in children under the age of 5 years. Infection with P.falciparum being the most deadly form of malaria. The vector transmitting the disease is Anopheles culicifacies mosquito. Regularly malaria presents fever, headache, vomiting and other flu-like symptoms and the parasite enters the blood stream and infects the blood cells and destroys them leading to anemia and extreme fatigue. Some severe symptoms include convulsions/fits, loss of consciousness. [1][2]



DENGUE:

Dengue is an emerging, outbreak-prone, mosquito-borne viral infection. More than 3.9 billion people in over 129 countries are at risk of contracting dengue, with an estimated 96 million symptomatic cases and an estimated 40,000 deaths every year. The disease is transmitted by Aedes aegypti mosquito. The symptoms of dengue include high fever, frontal headache, muscle and joint pains, pain behind the eyes, sometimes rash over chest and limbs. Sometimes it can lead to severe symptoms like vomiting with or without blood, bleeding from nose, skin rashes, difficulty in breathing. [1][2] 



FILARIASIS:

Filariasis is caused by round, coiled, thread-like parasitic nematode worms belonging to filaridea family and transmitted by ubiquitous mosquito species like Culex and Mansonia. The disease manifests as a bizarre painful swelling of legs, high fever, hydrocele. Patients may be bed-ridden for several days. Filariasis is one of the leading causes of disability worldwide. [2]



LEISHMANIASIS:

Leishmaniasis is caused by protozoan parasite of genus Leishmania and is transmitted by sandfly. The parasite infects the reticuloendothelial system. Some symptoms include recurrent fevers, loss of appetite, weight loss, splenomegaly, hepatomegaly, lymphadenopathy, anemia, skin is dry, thin, scaly with grayish discoloration. Mostly affects low socio-economic groups. [2]




JAPANESE ENCEPHALITIS:

Japanese encephalitis is a zoonotic viral disease caused by JE virus and transmitted from birds, pigs, and other animals. This may result in febrile illness with neurological symptoms like headache, fever, meningeal signs, stupor, disorientation, coma, tremors, paralysis, leading to meningitis or encephalitis. It is often difficult to differentiate JE and other viral encephalitis clinically. [2]



CHIKUNGUNYA:

Chikungunya is caused by the chikungunya virus and is transmitted by mosquitoes. The disease resembles Dengue in the presentation with symptoms like persistent joint pain, fever, and rash. As there is no specific treatment for chikungunya, it is better to prevent the disease by avoiding mosquito bites. [2]



PREVENTION BY VECTOR CONTROL:

Personal Measures:

  • Use insect repellent creams, liquids, coils, and mats.

  • Cover your body with full sleeve shirts and pants with socks.

  • Use of mosquito bed nets, mainly for children and infants.

  • Eliminating cracks in walls and perches which are shelters for ticks.

  • Flea traps can be utilized.

  • Getting vaccinated for the available vaccines.

  • Laundering pet bedding, sofa covers, bed coverings for Flea and tick larvae. [3][4]

Environmental Management:

  • Use of larvivorous fishes in places with stagnant water like fountains and tanks

  • Detection and elimination of breeding sources.

  • Detecting and controlling vectors during epidemics. [3][4]

Health education:

  • Creating awareness among the population regarding the disease and vector through media sources like T.V, radio, cinema, etc. [3][4]

Advise for travelers:

  • Consult your doctor for travel health assessment before traveling to places which are endemic to vector-borne diseases for prophylaxis, vaccinations, and vector preventive measurements.

  • During camping, hiking, or trekking do not rest on vegetation or humid dark places and inspect body parts and clothing for any attached arthropods and clear them.

  • Carry insect repellents and mosquito nets to prevent insect bites. [4]



Author: Dr. Mukkamala Sai Priya Chandana, MBBS, Shadan Institute of Medical Sciences, Hyderabad, India.


Editor: Dr. Sidhant Ochani, MBBS, Khairpur Medical College, Khairpur, Pakistan. 


REFERENCES:



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