What Is the Impact of Vector-borne Diseases?

Malaria
Vector-borne diseases cause more than 1 million deaths annually.6 Approximately 3.2 billion people – almost half of the world’s population – are at risk of malaria, which has ongoing transmission in 95 countries and territories. Sub-Saharan Africa carries a disproportionately high share of the global burden, and in 2015 was home to 88% of malaria cases and 90% of malaria deaths.7Malaria is an acute febrile illness, causing fever, headache, chills, and vomiting in non-immune individuals. If not treated within 24 hours, infections caused by the Plasmodium falciparum malaria parasite can progress to severe illness, often leading to death. The majority of deaths are in children under 5 years of age.8The disability-adjusted life year (DALY) is a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death. When considering vector-borne diseases with this metric, malaria stands out as having the greatest disease burden worldwide, considerably greater than all other vector-borne diseases (Table 1). By comparison, microcephaly and Guillain-Barré syndrome from Zika have been predicted to cause a loss of 43,717 to 108,951 DALYs, if an attack rate of 5% is assumed.9The direct costs of malaria, including illness, treatment, and premature death, have been estimated to be at least US$12 billion per year. On top of this is lost economic growth, which is likely to be many times more than that.10Disease | Million DALYs |
---|---|
Mosquito-borne infections | |
Malaria | 46.5 |
Lymphatic filariasis | 5.8 |
Dengue | 0.62 |
Japanese encephalitis | 0.71 |
Yellow fever | No data |
Others | |
Onchocerciasis | 0.48 |
Leishmaniasis | 2.1 |
African trypanosomiasis | 1.5 |
Chagas | 0.67 |
Lymphatic filariasis
Lymphatic filariasis, commonly known as elephantiasis, is a neglected tropical disease. Infection occurs when thread-like parasitic worms are transmitted to humans through mosquito bites. When these worms grow to their adult stage they can become lodged in the lymphatic system and disrupt the immune system. In severe cases this leads to fluid retention and tissue swelling in the limbs or genitals, and patients suffer from social stigma, as well as financial hardship through loss of earnings or medical expenses.Approximately 1.1 billion people in 55 countries are living in areas that require preventive drugs to stop the spread of infection. Close to 80% of these people are living in just 10 African and Asian countries: Angola, Cameroon, Côte d’Ivoire, Democratic Republic of the Congo, India, Indonesia, Mozambique, Myanmar, Nigeria, and the United Republic of Tanzania.12 A total of over US$800 million is estimated to be lost per year due to lymphatic filariasis in India alone.13Dengue
Dengue is a mosquito-borne viral infection that causes a flu-like illness, and occasionally develops into a potentially lethal complication called severe dengue, or Dengue Haemorrhagic Fever. Recent decades have seen a significant growth in the incidence of this disease, and now more than 2.5 billion people in over 100 countries are at risk of contracting the virus.14Dengue is usually a self-limited illness, and there is no specific antiviral therapy available for it. Treatment involves trying to relieve the symptoms, and with early detection and medical care the fatality rate can be reduced below 1%.14Japanese encephalitis
Related to the dengue virus is the Japanese encephalitis (JE) virus, which is the main cause of encephalitis in many Asian countries. Currently, 24 countries in South-East Asia and Western Pacific regions have endemic JE virus transmission, with over 3 billion people at risk of infection. Encephalitis is a serious condition that causes the brain tissue to become inflamed. There is no cure for this disease, so treatment is focused on supporting the patient and relieving their severe clinical symptoms15. Fortunately less than 1% of people infected with JE virus develop clinical illness.16Other vector borne diseases
The diseases considered above are all transmitted by mosquitoes, but other important vectors include sandflies, tsetse flies, black flies, triatomine bugs, fleas, ticks, and some aquatic snails.7 The pathogens themselves vary from viruses to bacteria, protozoa, and filarial worms, and collectively they are responsible for hundreds of millions of cases of disease in humans and animals each year.The most important vector-borne diseases occur in the tropics, usually in the areas where resources are the most limited and there is very poor surveillance. However, over the past 30 years there has been an expansion in the geographical distribution of vector-borne diseases and they now present the world community with possibly its greatest health problem and threat to economic security today.17To conclude
At some stage the explosive outbreak of Zika we have seen in the Americas is expected burn out as an increasing number of people gain immunity. What will happen after that remains unknown; Zika may behave like dengue and other viruses, recurring regularly with spikes in the rainy seasons, or sufficient immunity may be established to cause the virus to die out altogether.18 While most people infected with Zika will have either no symptoms or only mild symptoms, it is now understood that serious manifestations and complications have resulted in some deaths, and it is still too early to accurately rank the impact of Zika against the other vector-borne diseases.Preventing the Zika Virus: Understanding and Controlling the Aedes Mosquito

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