Beyond Zika: What to Know About Mosquito-Borne Diseases

Many Americans think of mosquitoes in general terms: a mosquito bite results from a mosquito. However, there are different types of mosquitoes out there, and different types of mosquitoes inflict more than just the nuisance of a generic localized allergic reaction or itchy red bump. Different mosquitoes can spread different kinds of serious illnesses.

For example, the Culex genus of mosquitoes spreads West Nile virus, St. Louis encephalitis and arboviridae. Mosquitoes belonging to the Anophelus genus spread malaria. And then, Aedes mosquitoes-primarily Aedes aegypti but also Aedes ablopictus-spread yellow fever, dengue, chikungunya, and Zika virus.

One major factor that contributes to the ability of a mosquito to successfully spread illness is its specific preference for habitat. Culex pipiens, which spreads West Nile, loves stagnant, polluted, and dirty water. Anopheles species, which spread malaria, prefers permanent water sources, such as lakes, ponds, and swamps.

In contrast, Aedes aegypti, which spreads the Zika virus, dengue, and chikungunya, is a floodwater mosquito that can breed in relatively small amounts of water, including small containers. Unlike Aedes ablopictus, which is more of a rural mosquito and is less active in spreading diseases including Zika virus, Aedes aegypti has a special preference for urban areas.

Taken together, these habitat preferences explain why there's been an explosion of Zika virus in wet, damp, heavily populated environments like those of Brazil. As you may have heard, about 4000 cases of newborn microcephaly, many thought to be related to maternal Zika virus infection, were observed in Brazil in 2015.

Here are six different mosquito-borne illnesses.


Yellow Fever

Print of Panama Canal Construction c. 1890

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In 1904, Americans began construction on the Panama Canal (after the French abandoned the project), which today joins the Atlantic and Pacific Oceans. By 1906, 85% of the workforce had been hospitalized with yellow fever or malaria. Of these two mosquito-borne illnesses, yellow fever was considered more deadly.

Yellow fever is primarily transmitted by the Aedes aegypti, which is also known as the yellow fever mosquito. Hot beds for infection include Africa and Latin America. Symptoms of yellow fever can range from mild illness to viral hemorrhagic fever. (Ebola and dengue can also cause viral hemorrhagic fever.)

Yellow fever kills about 20% of all people that it infects. Severe symptoms include persistent fever, seizures, vomiting, headache, arrhythmias, coma, and shock. The classic triad of symptoms consists of albuminuria (protein in the urine), jaundice (which is why this illness is called yellow fever) and black emesis, or vomit. Learn how it's diagnosed.

Treatment for yellow fever is symptomatic and includes medications for pain relief and fluids. There is a very effective vaccination that prevents yellow fever.



Asian Tiger Mosquitos

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Like yellow fever, chikungunya is spread by Aedes aegypti. Chikungunya is also spread by the Asian tiger mosquito (Aedes albopictus).

Probably the only good thing about chikungunya, other than its hilarious name, is that this disease won't kill you. Nevertheless, if you are unfortunate enough to be infected with this illness, be prepared for one helluva week-long ride.

Chikungunya causes severe joint pains, headache, fever, and rash. Joint pain may persist for years after infection.

Other than supportive treatment, like fluids and pain medications such as Tylenol, there is nothing to do for chikungunya. There is also no vaccination to prevent this illness. People who live in areas where chikungunya is endemic should wear insect repellent and cover up to prevent mosquito bites.



Aedes aegypti

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Dengue is spread by both Aedes aegypti and Aedes albopictus.

Dengue presents a lot like chikungunya; fever, rash, and headache are all par for the course. However, instead of the joint pains (arthralgia) more typical of chikungunya, dengue presents with muscle pains or myalgias. This muscle pain can be so intense that dengue has exacted its moniker: "breakbone fever."

Most people with dengue fever recover. Unfortunately, some go on to develop dengue hemorrhagic fever, which is deadly without early and aggressive supportive care as well as intravenous fluids, blood transfusions, and other acute care. People with dengue hemorrhagic fever who are left untreated end up bleeding from many parts of the body and can die from shock.

Dengue fever is treated symptomatically, and no cure exists.

After 20 years of research, the French pharmaceutical firm Sanofi created a vaccination for dengue in 2015.



Anopheles Mosquito

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Malaria is spread by Anophelus mosquitoes, which carry the parasite Plasmodium.

Malaria is responsible for a whopping one million deaths a year; it spreads unabated in many developing nations with tropical and subtropical environs.

Here are some common symptoms of malaria:

  • Intermittent attacks of fever, sweating, and chills
  • Headache
  • Vomiting
  • Muscle pain (myalgia)
  • Anemia
  • Thrombocytopenia (destruction of platelets)
  • Splenomegaly (enlarged spleen)

Severe infection with malaria entails life-threatening organ damage, hypotension (dangerously low blood pressure), pulmonary edema (fluid in the lungs), severe anemia, metabolic (body-salt) disturbances and more. Learn how malaria is diagnosed.

Fortunately, antimalarial drugs are effective at treating malaria; chloroquine is first-line treatment.

Antimalarial drugs can also be used as prophylaxis to prevent malaria in travelers.


West Nile Virus

Culex Pipiens mosquito on a person's arm

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On the Eastern seaboard of the United States, Culex pipiens spreads the West Nile virus. Unlike the other aforementioned mosquitoes, which spread infection among humans, Culex pipiens transmits West Nile after biting a bird first and then a human second.

Most people who are infected with West Nile virus come down with no symptoms and are therefore asymptomatic. The CDC estimates that one of five people infected with West Nile virus develop mild clinical symptoms, including fever, vomiting, diarrhea, rash, as well as aches and pains.

A minority of people — mostly people older than 60 years old with conditions like diabetes, hypertension, or cancer — go on to develop a severe infection. Severe infection involves neurological problems: meningitis or encephalitis. About 10% of people who develop such severe infection die.

There is neither a cure nor vaccine for West Nile virus. For people with mild illness, symptomatic treatment is given. People with severe illness need supportive care and hospitalization.


Zika Virus

Aedes aegypti zika mosquito
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Like dengue, yellow fever, and chikungunya, the Zika virus is primarily spread by Aedes aegypti. It also has similar symptoms to these other diseases.

In early 2016, the WHO declared that the Zika virus was a global health emergency in light of a harrowing link to microcephaly and other birth defects among Brazilian newborns. Learn how Zika is diagnosed and treated.

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