Vector Borne Disease

A vector-borne disease is caused by a pathogenic microorganism transmitted by an arthropod or other agent. Mosquitoes are one of the deadliest animals in the world, spreading diseases such as Dengue, Lymphatic Filariasis, Zika and Malaria. Vectors such as sandflies, black flies, tsetse flies and mosquitoes cause 17% of all infectious disease burden.

Transmission of vector-borne disease requires at least three different organisms:

  • Pathogenic agent (causes the disease e.g. a bacterium, virus or fungus)
  •  Vector (carries the disease and disperses reproductive structure)
  •  A human host

According to WHO, there are more than 1 billion cases and over 1 million deaths from vector borne diseases a year globally. These devastating diseases have an overwhelming impact in developing countries in the tropics.

Many different factors such as climate change, growing urbanization and changes in agricultural methods cause levels of disease transmission to fluctuate. People displaced and caught up in conflict or natural crises are even more vulnerable to VBD since little or no shelter and poor sanitation increases exposure to vector contact. Alongside malnutrition in the poorest communities, multiple infections decrease the ability of the immune system, meaning that the body cannot fight preventable diseases.

With our expertise and experience in vector borne disease, MENTOR works to educate others of the epidemiology of different types of diseases and how to prioritize key control measures. Through implementing evidence-based control programmes across the world, MENTOR provides those most in need with prevention, surveillance and control of vector borne disease.

Dengue is transmitted by infected female mosquito – Aedes aegypti, primarily a daytime feeder.

Dengue is transmitted by the Aedes Aegypti mosquito which, unlike other mosquitoes, is day biting. Symptoms include fever, headache, muscle and joint pains and the disease can develop into the fatal dengue haemorrhagic fever. There is no current vaccine for dengue, therefore, the best way to eradicate this dangerous disease is to protect against bites and control the vector. Outbreaks of dengue are becoming more numerous and more serious, with 50 million cases annuallyestimated by the WHO.

Read about MENTOR’s response to the Ebola outbreak in Liberia. 

Ebola is caused by a virus that is transmitted through direct contact with bodily fluids and cannot be diagnosed based on symptoms alone. As a viral hemmorrhagic fever, Ebola is highly infectious and the risk of human-to-human transmission is extremely high.  Early symptoms are flu-like, followed by vomiting, diarrhoea, a rash and external and internal bleeding. Intravenous re-hydration and intensive care can help recovery but neither are readily available within the weak health systems of the countries most affected such as Liberia, Guinea and Sierra Leone. Ebola is most typically found in areas of humid climate and rain forest environments in Central and West Africa. Click here to read about MENTOR’s work in Liberia during the Ebola crises.

Leishmaniasis is one of the world’s most neglected tropical disease. Transmitted by the bite of the female phlebotomine sand flies and cause by protozan parasites from the genus Leishmania, these diseases are devastatingly disfiguring and can be fatal.

There are three types of Leishmaniasis:

1.    Visceral leishmaniasis (VL; kala-azar) which is fatal if left untreated;

2.    Cutaneous leishmaniasis (CL) which is typically the most common, causing skin lesions that can be self-resolving but if untreated can lead to mucocutaneous lesions. In its more common clinical presentation, it is known as “Silent Sheikh,” “Oriental Sore,” “Aleppo Boil”

3.    Mucocutaneous lesions can lead to partial or total destruction of the mucous membranes of the nose, mouth and throat cavities and surrounding tissues.

According to the World Health Organization, 310 million people are at risk of infection in six countries reporting over 90% Visceral Leishmaniasis cases worldwide.

Lymphatic Filariasis is a painful and disfiguring disease, more commonly known as elephantiasis. Caused by three species of filarial (thread-like) worm in humans, this parasitic infection can result in an altered lymphatic system and abnormal enlargement of body parts. This disease has devastating social and economic consequences due to its visibility and disabling manifestations. LF is one of the world’s neglected tropical diseases.

Transmission of LF can be reduced by controlling the vector, Culex, Anopheles and Aedes mosquitoes. Through methods such as long lasting insecticidal nets or indoor residual spraying, people are protected from infection. To stop the spread of infection, large scale distribution of the drugs albendazole combined  ivermectin or diethylcarbamazine citrate can clear microfilariae from the bloodstream, preventing the spread of parasites to mosquitoes.

Epidemics of LF usually occur in Asia, Africa, and Central and South America.

Over 120 million people are infected and more than 1.3 billion people are at risk of Lymphatic Filariasis.

Schistosomiasis is caused by adult parasitic flatworms (Schistosoma) which develop from skin-penetrating larvae released by freshwater snails. The adult female shistosoma live in the blood vessels and release eggs which can be passed out in excreta, often contaminating freshwater sources, or stay in the body and damage organs and blood vessels. Access to clean water and sanitation is one of the most important factors in controlling and eliminating this disease.

According to WHO, at least 261 million people required preventative treatment for schistosomiasis in 2013.

Commonly known as parasitic worms, soil-transmitted helminth (STH) infections affect the poorest communities and are transmitted to humans by faecally-contaminated soil. The eggs, passed in faeces, can be ingested in different ways: when vegetables are not carefully cooked or washed, from contaminated water sources or by children who play in the contaminated soil, putting their hands in their mouths without washing them. Furthermore, hookworm eggs hatch in soil and can penetrate the skin of people walking barefoot on the contaminated soil.

Affecting more than 2 billion people worldwide, STH have a chronic, gradual but harmful impact on the health and quality of life of those infected. Through regular treatment of children in endemic areas, health and hygiene education and provision of adequate sanitation, STH infections can be eliminated.

Trachoma is a bacterial eye infection, also called granular conjunctivitis. In advanced stages, the eyelashes turn inwards, scratching the cornea and causing permanent blindness. Trachoma is caused by an organism called Chlamydia trachomatis and the infection usually first occurs in childhood. Infections can spread through the discharge from an infected child’s eye, passed on clothing, hands or by flies landing on children’s faces.

According to WHO, six million people worldwide are blind due to trachoma but it is entirely preventable with better hygiene practice. MENTOR implements Water, Sanitation, and Hygiene (WASH) activities which encourage the washing of children’s hands and faces alongside improving access to clean water and proper waste disposal.

Yellow fever is a serious viral infection that’s spread by the infected Aedes aegypti mosquito. The ‘yellow’ in the name refers to the jaundice that affects some patients. Up to 50% of those severely affected die from yellow fever if left untreated.  The first symptoms usually consist of fever, muscle pain, prominent back ache, headache, shivers and nausea/vomiting. The second phase can affect several body systems with kidney function deteriorating. Vaccination, mosquito control and epidemic preparedness and response are the main ways of combating yellow fever.