9 disturbing facts about malaria and other deadly vector-borne diseases

Today, on World Health Day, the World Health Organization (WHO) is drawing attention to one of the biggest public health threats facing people globally — vector-borne diseases.

As the name suggests, this group of diseases is caused by vectors — organisms that transmit parasites and bacteria from infected persons (or animals) to other people. Common examples include mosquitoes, flies, sandflies, ticks, bugs and freshwater snails.

Some of these diseases are household names, such as malaria, dengue, yellow fever, plague, typhus, West Nile virus and Lyme disease. Others may be less well known, such as Chagas disease, schistosomiasis, leishmaniasis and lymphatic filariasis.

So why are they the focus of World Health Day?

Because they cause an untold amount of suffering, illness and death around the world. And those who survive are often left “permanently debilitated, disfigured, maimed, or blind,” says the WHO. Dr. Neeraj Mistry of the Global Network for Neglected Tropical Diseases writes for CNN:

These diseases… are one of the major reasons for lower economic productivity among adults and decreased school attendance among kids in poor and even middle-income countries, and pose a primary obstacle to achieving many of the Millennium Development Goals, particularly for education, nutrition, and maternal and child health.

But here’s the good news — many vector-borne diseases can be prevented, controlled and eliminated through existing technologies, medicines and vector-control measures.

In honor of World Health Day 2014, here are some astonishing facts about vector-borne diseases.

1. They infect more than one billion people worldwide — including over 500 million children — and cause at least one million deaths annually.

As little as 11 cents can protect someone from river blindness for a year by ensuring the treatment reaches the communities in need. (Kate Holt/Sightsavers – Courtesy)

Vector-borne diseases account for 17 percent of all infectious disease suffered worldwide. And various environmental and social factors increase their potential to spread, including “changes in climate, ecology, land-use patterns, and the rapid and increased movement of people and goods,” says the WHO.

2. They thrive in conditions of poverty and inequality, particularly in developing countries.

A child faces the water in Cite Soleil, the biggest slum in Port-Au-Prince April 28, 2010. (Thony Belizaire via AFP/Getty Images)

Vector-borne diseases affect the least developed countries and the poorest segments of society within countries. Commonly found in tropical and sub-tropical regions, they’re also known as “neglected tropical diseases.” They thrive where people experience poor living conditions, including a lack of access to adequate housing, safe drinking water and sanitation systems, and exposure to areas of environmental degradation.

3. Malaria is the world’s most deadly vector-borne disease.

Malaria is the world's deadliest disease, with more than one million people, most of them young African children, dying from it every year. (Spencer Platt via Getty Images)

Malaria is a mosquito-borne illness that causes fever, chills and a flu-like illness. If left untreated, it can lead to severe illness and death. More than 3.4 billion people are at risk of malaria in 97 countries. It kills over 600,000 people each year, most of them children under five. Around 90 percent of all malaria deaths occur in sub-Saharan Africa, particularly in the Democratic Republic of the Congo and Nigeria. “The best way to prevent malaria infection is through the regular use of long-lasting insecticidal nets, indoor spraying of homes with residual insecticides, and the use of WHO-recommended preventive therapies,” states the WHO.

4. More than 40 percent of the world's population is at risk of dengue.

Pakistani patients affected with dengue fever share beds in a ward at the hospital in Lahore on September 7, 2011. (Arif Ali via AFP/Getty Images)

Dengue is a “mosquito-borne infection that may cause lethal complications.” More than 2.5 billion people in 100 countries are at risk of dengue, which causes 100 new infections every year. Dengue is the most rapidly spreading mosquito-borne viral disease in the world, with a 30-fold increase in new infections over the past half century. No effective medications exist to prevent or treat dengue, and the only method to reduce transmission is to control mosquitoes and protect against mosquito bites.

5. Leishmaniasis kills or disfigures thousands of people every year, especially in conflict zones.

The Afghan capital, Kabul, has one of the highest concentrations of the disfiguring skin disease, Cutaneous leishmaniasis, which is a parasitic disease transmitted by a sand fly. (Majid Saeedi via AFP/Getty Images)

Leishmaniasis, transmitted by the bite of infected sandflies, can cause fever, weight loss, spleen and liver enlargement, anaemia, rashes and skin ulcers. The disease infects 1.3 million new people and kills around 30,000 people each year, particularly in the Americas, Asia, east Africa and the Mediterranean. “Among those most vulnerable to vector-borne tropical infections are people who live in conflict zones such as in Syria or Sudan,” writes Dr. Peter Hotez of Baylor College of Medicine for the Huffington Post. “Over the last few decades, leishmaniasis has killed or disfigured hundreds of thousands of people in these war-torn areas.”

6. Snail fever (schistosomiasis) can cause anemia, stunting and learning impairment in children.

Villagers' samples await testing for snail fever, or schistosomiasis, as a medic works at a clinic in a village outside of Yueyang, 31 October 2004, in central China's Hunan province. (Frederic J. Brown via AFP/Getty Images)

Schistosomiasis is caused by parasitic flatworms (blood flukes) transmitted by freshwater snails. People contract the disease when they come into repeated contact with infected water — often through routine activities such as water collection, laundry, bathing, fishing and farming.

One of the signs of schistosomiasis is blood in the urine. More than 700 million people are at risk of infection from the disease, which has been documented in 78 countries. The WHO notes that some 249 million people were treated for schistosomiasis in 2012.

7. Elephantiasis (lymphatic filariasis) inflicts significant pain, disfigurement and social exclusion.

A man with elephantiasis of leg due to filariasis in Luzon, Philippines. (Wikimedia Commons)

This chronic disease, which affects men more than women, “occurs when filarial parasites are transmitted to humans through mosquitoes.” Symptoms include damage to the kidney, lymphatic system and immune system, as well as swelling of the arms, legs and genitals. Lymphatic filariasis infects more than 120 million people worldwide, including 40 million who are disfigured and debilitated by the disease. Around 65 percent of those infected live in southeast Asia, 30 percent live in Africa and the rest in tropical areas throughout Asia and Latin America.

8. Around 37 million people worldwide suffer from river blindness.

Women wash clothes in the river close to their village. Rivers like this one are where the flies that spread river blindness breed. (Kate Holt/Sightsavers – Courtesy)

Onchocerciasis is a parasitic disease transmitted by filarial worms which infects around 37 million people. It causes intense itching and skin depigmentation, lymph node enlargement producing hanging groins and elephantiasis of the genitals, visual impairment and blindness. It’s the world’s second leading cause of blindness from infectious disease and occurs in 31 countries in Africa, central and southern Latin America, and Yemen.

9. Chagas disease is endemic in Latin America and causes progressive cardiac, digestive and neurological damage.

Community health workers conduct a training on preventing Chagas disease in Aquile, Bolivia. (SolidarityBridge via YouTube)

Chagas disease, also known as American trypanosomiasis, is a “life-threatening condition transmitted through triatomine bugs, contaminated food, infected blood transfusion.” Around 10 million people are infected with the disease. Although it was once confined to the Americas, Chagas disease is spreading to other continents through increased travel, migration, blood transfusion and organ donation.

To read about other vector-borne illnesses, as well as what's being done to prevent and control them, visit the WHO’s website here.

Sources: WHO Vector-borne diseases factsheet | WHO A global brief on vector-borne diseases