Many diseases, such as malaria and dengue fever, can be transmitted through mosquitoes. Malaria is a disease spread by mosquitoes that bite between dusk and dawn. It is a risk in many countries in the world. There is no vaccine against malaria, but medications, called anti-malarials, are available. Diseases relayed by mosquitoes such as malaria, dengue fever, yellow fever and several kinds of encephalitis are among those eliciting the greatest concern as the world warms.
Cold can be a friend to humans, because it limits mosquitoes to seasons and regions where temperatures stay above certain minimums. Winter freezing kills many eggs, larvae and adults outright. Anopheles mosquitoes, which transmit malaria parasites (such as Plasmodium falciparum), cause sustained outbreaks of malaria only where temperatures routinely exceed 60 degrees Fahrenheit. Similarly, Aedes aegypti mosquitoes, responsible for yellow fever and dengue fever, convey virus only where temperatures rarely fall below 50 degrees F.
Global warming is allowing the species primarily responsible for spreading dengue (Aedes aegypti, also known as the yellow fever mosquito) to expand its range. Population growth in developing nations is pushing more people into substandard housing in mosquito-infested areas. And the ease of travel brings the virus to areas that were previously dengue-free when a mosquito bites an infected traveler and then spreads it to others.
Dengue is now one of the most important tropical diseases. A member of the same family of viruses that causes West Nile, Japanese encephalitis and yellow fever, dengue fever is a potentially fatal disease for which there is no vaccine or treatment despite estimates that it infects at least 50 million people a year. Physicians generally have little reason to suspect malaria, as the sufferers may never have traveled to a region where the disease is endemic and the symptoms can sometimes be confused with flu.
A severe achy-joint fever (called chikungunya, is ravaging parts of Indonesia, sickening people with rashes, vomiting, headaches) spreading in Asia via mosquitoes could easily reach more countries in the region and potentially take hold in Europe and the United States, World Health Organization experts warn; reported recently (01/19/2008).
As of January 25, 2008, the Singapore Ministry of Health (MOH) had reported 11 probable cases of chikungunya fever in a localized area of Singapore. A lack of recent travel among cases and clustering of cases in a small geographic area suggests that there has been local transmission of chikungunya virus through mosquitoes in Singapore.
"With international travel being easy and fast, it is easy for the virus to be imported into a new region," said Stephen Higgs, co-author of the University of Texas findings published last month in the Public Library of Science journal PLoS Pathogens.
Singapore reported eight suspected cases this week, the first time the virus has spread locally, according to a Ministry of Health statement. Taiwan also detected three cases in travelers from Indonesia, two in December and another earlier last year. Nearly 300 people in northern Italy were sickened in 2007 after an infected traveler came from India, the first time an imported case of the tropical disease sparked a local outbreak in Europe.
The resurgence of dengue is one of the quiet disasters of modern public health. In 30 years, only nine countries reported chronic outbreaks. Until 1980, deadly dengue hemorrhagic fever was unheard of in the New World. In 2005 at least 127,000 people have been infected by dengue so far this year from eastern India to Indonesia and the Philippines, with at least 990 deaths.
Northern Africa (Algeria, Egypt, Libyan Arab Jamahiriya, Morocco, Tunisia) have risk of malaria. Sub-Saharan African countries also have risk of mosquito born diseases such as malaria, filariasis, relapsing fever, typhus, plague, yellow fever, hemorrhagic fevers (such as Dengue hemorrhagic fever, etc.) Children who are visiting family and relatives living in developing countries are at high risk for a variety of travel-related health problems, including malaria, intestinal parasites, and tuberculosis.
Thirty-three countries, with a combined population of 508 million, are at risk in Africa. These lie within a band from 15°N to 10°S of the equator. In the Americas, yellow fever is endemic in nine South American countries and in several Caribbean islands. Bolivia, Brazil, Colombia, Ecuador and Peru are considered at greatest risk.
The virus is constantly present with low levels of infection (i.e. endemic) in some tropical areas of Africa and the Americas. This viral presence can amplify into regular epidemics. Until the start of this century, yellow fever outbreaks also occurred in Europe, the Caribbean islands and Central and North America. Even though the virus is not felt to be present in these areas now, they must still be considered at risk for yellow fever epidemics.
Mexican state of Sonora reported number of dengue fever cases in 2004.The dengue fever season in Sonora is seasonal and peaks mid-October, after the summer rainy season.
On January 8, 2008, the Brazilian Ministry of Health (MOH) announced a yellow fever disease alert for tourists and diplomats residing in Brazil, due to a number of suspected and confirmed human yellow fever cases during December 2007 and January 2008. As of January 23, 2008, 18 confirmed cases of Yellow Fever have been reported, including nine deaths.
The Brazilian MOH alert states that travelers to “areas of risk” for yellow fever should be vaccinated 10 days before going to such areas. In addition to areas previously identified in CDC’s guidance to travelers, the Brazilian MOH has identified two additional states with yellow fever risk: the northern part of Espiritu Santo and the western part of Santa Catarina.
Dengue fever -- a tropical infection that usually causes flu-like illness, but which can be deadly -- may be poised to spread across the United States and urgent study is needed, health officials said recently (Jan 2008).
Cases of the mosquito-borne disease have been reported in Texas and this may be the beginning of a new trend, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, and his senior scientific adviser, Dr. David Morens.
A warming climate and less-than-stellar efforts to control mosquitoes could accelerate its spread northwards, they cautioned.
"Widespread appearance of dengue in the continental United States is a real possibility," they wrote in a commentary in the Journal of the American Medical Association.
Take these steps to protect yourself:
• Apply insect repellent according to product directions to prevent mosquito and other insect bites.
• For adults, insect repellent should contain 30%-50% DEET or picaridin, which is available in 7% and 15% concentrations but needs more frequent application. There is less information available on how effective picaridin is at protecting against all of the types of mosquitoes that transmit malaria. For detailed information about insect repellent use, see Insect and Arthropod Protection.
• Wear long pants, long-sleeved clothing, and a hat outdoors.
• Consider applying permethrin (often found in stores with the camping equipment) to the clothing that you will be wearing during your trip as an additional layer of mosquito bite prevention.
• Sleep under an insecticide-treated bed net, especially if you are not staying in screened or air-conditioned housing.
• Visit a health care provider, ideally 4-6 weeks before your trip. Also ask your health care provider or pharmacist for clear directions about how to take the medicine properly. It is still important to prevent mosquito bites even if you are taking medicine.
After you return home if you feel sick during or after your trip (for up to 1 year), especially with a fever, you should see a health care provider right away. If you are back home, make sure to tell the health care provider that you have recently traveled.
Mosquitoes that transmit malaria are most active between dusk and dawn, while dengue is commonly transmitted by day-biting mosquitoes. Mosquitoes are only one of the concerns to take into account when preparing for travel. You can learn more about the recommended vaccinations and prevention tips for your travel on the CDC Travelers Health Web site.
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