Mosquitoes are considered one of the most dangerous creatures on the planet because of their ability to spread deadly diseases.
The U.S. Centers for Disease Control report that the insects kill more than one million people a year just through the transmission of malaria. Add to that the numbers of those sickened and killed by other mosquito-borne diseases such as dengue fever, yellow fever and West Nile virus, and it’s easy to see how they earned their dangerous reputation. In recent years the rate of infection has risen dramatically, and a growing number of scientists are now concerned that global warming will translate into an explosive growth of mosquito-borne diseases worldwide.
These are some of the most prevalent diseases spread around the world by mosquito bites:
Having spread to almost every country in the Americas, on 1 February 2016, the Zika virus was declared a global public health emergency by World Health Organization Director-General Margaret Chan, who called it an “extraordinary event“. On 13 April 2016, the U.S. Centers for Disease Control and Prevention released a report confirming that the Zika virus does cause a rare birth defect called microcephaly – a neurological disorder that results in babies being born with abnormally small heads and developmental issues.
The Zika virus is typically transmitted by the Aedes aegypti mosquito, but it can also be spread sexually, causing the CDC to update its guidance to couples. Aedes aegypti mosquitoes are aggressive daytime biters and officials are warning people of the need to be vigilant, cover up and reapply repellent regularly. The Asian tiger mosquito (Aedes albopictus) which is also established throughout the United States, and transmits dengue fever and Chikungunya, may also be capable of transmitting the Zika virus.
There is no vaccine, treatment or cure for the disease and travelers to infected areas are being urged to prevent mosquito bites as the best and only protection against the disease. Pregnant women are being warned against travel to countries where Zika is present because of risk to their unborn babies.
Most people infected with Zika (80%) have no symptoms or don’t realise they have it because symptoms are typically mild. Common signs to look out for include slight fever, rash, joint pain and conjunctivitis (red eyes).
The World Health Organization estimates 3 to 4 million people across the Americas, will be infected with the virus in the coming year. To date the Zika virus is now being locally transmitted in Barbados, Bolivia, Brazil, Cape Verde, Colombia, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Saint Martin, Suriname, American Samoa, the U.S. Virgin Islands and Venezuela.
Caused by parasites, primarily Plasmodium falciparum or Plasmodium vivax. Female Anopheles mosquitoes pick up the parasites by feeding on infected humans. The parasites develop in a mosquito’s body for 10 to 18 days, then is passed on when the mosquito injects saliva while feeding.
Once in the human body, malaria parasites migrate to the liver, where they grow and multiply. Eventually the parasites move into the blood stream to continue developing in red blood cells. As they multiply and are released, they destroy the blood cells.
This is the stage when those infected begin to show symptoms such as fevers, chills, sweating, headaches and other flu-like conditions. The infection can sometimes produce even more severe reactions, including kidney failure and death, especially if left untreated.
Quinine and other anti-malarial drugs cure patients by attacking the parasites in the blood.
West Nile virus
A viral infection carried in the blood of birds. Culex mosquitoes pick it by feeding on infected birds, then, after it spreads through their systems, pass it to humans through their saliva during feeding.
The West Nile virus multiplies in the human blood stream and is carried to the brain, where it begins to affect the central nervous system and causes inflammation of brain tissue, known as encephalitis. If this happens, a person will develop high fever, headaches, swollen lymph nodes and stiff neck.
In the most severe cases, the infection can lead to convulsions, coma and death. Even if a severely infected person survives, there is a good chance of permanent neurological damage.
There is no specific treatment of West Nile virus.
However, only one in 150 people infected with West Nile virus experience severe symptoms. People over 50 are most at risk. About 80 percent of those infected show no symptoms at all, according to the CDC.
Researchers believe that people who are infected once develop a natural immunity to West Nile virus that will last the remainder of their lives.
Another infection caused by one of four viruses common to tropical and subtropical climates. The disease is spread by Aedes mosquitoes in much the same way as West Nile and other encephalitic viruses. A mosquito is able to transmit dengue about a week after biting an infected person.
As the dengue virus multiplies and damages cells, an infected person begins to show symptoms similar to other infections: High fever, headaches, back and joint pain, rashes and eye pain. If the fever lasts up to a week and is followed by bruising and bleeding, those are symptoms of dengue hemorrhagic fever.
The fatality rate for hemorrhagic fever is about 5 percent, according to the CDC.
About 100 million people worldwide are infected with dengue each year, especially in Africa and the tropical Western Hemisphere. Hemorrhagic fever cases are estimated in the hundreds of thousands. It is more common to Southeast Asia, where children are especially susceptible.
Like most viruses, there is no specific treatment. Doctors recommend acetaminophen, plenty of fluids and rest for dengue and hospitalization for hemorrhagic fever.
A flavivirus orginally common to primates in Africa and South America. Like dengue, it is transmitted by Aedes mosquitoes, especially Aedes aegypti, the yellow fever mosquito.
The virus incubates in the body for three to six days before an infected person begins to show the common infection symptoms of fever, chills, headache and nausea. There may be a short remission before the disease returns with much more serious symptoms such as nosebleeds, bloody vomit and abdominal pain.
Fatality rates range from 15 to 50 percent.
While there is no treatment for yellow fever, it is possible to be vaccinated against infection for those living in or traveling to climates where the disease is prevalent.
Chikungunya fever is caused by a virus that is spread to people through the bite of infected mosquitoes. Like Dengue, it is transmitted by Aedes mosquitoes, especially Aedes aegypti (the yellow fever mosquito) and Aedes albopictus (the Asian tiger mosquito).
The incubation period is usually 3-7 days and symptoms can include sudden fever, joint pain with or without swelling, chills, headache, nausea, vomiting, lower back pain and a rash.
There is currently no vaccine to prevent Chikungunya. Management of the disease includes rest, fluids and medications to relieve the symptoms of fever and pain, such as ibuprofen, naproxen and paracetamol.