Mosquito-borne illnesses have long plagued the tropics, but the invasion of the Asian tiger mosquito (Aedes albopictus) into temperate zones dramatically increases the risk to human health. Because it bites aggressively and during daylight hours, it poses a greater threat to humans than other mosquito species. This article surveys the diseases carried by the Asian tiger mosquito worldwide.
* Diseases: Temperate Zones *
West Nile virus was identified in Africa in 1937, and discovered in the United States in 1999. It is related to Japanese Encephalitis, a serocomplex that is distributed worldwide.
West Nile spreads when an Asian tiger mosquito, or other vector (a vector is any creature that carries a disease without contracting it), bites an infected bird and then bites a person. Most infected people have no symptoms or ill effects, but some develop mild disease characterized by flu-like symptoms: fever, abdominal pain, diarrhea, headache, muscle aches, nausea, vomiting, etc. The infection can last for up to six days.
West Nile can lead to life-threatening encephalitis (swelling of the brain) or meningitis (infection of the membranes of the brain and spinal cord). Patients experiencing confusion, stiff neck, loss of consciousness, muscle weakness, or weakness of one arm or leg should seek immediate medical attention.
Eastern Equine Encephalitis (EEE) is rare in humans, and like West Nile, most infected people have no ill effects. Severe cases are characterized by sudden headache, fever, chills, and vomiting. Symptoms may progress to disorientation, seizures, or coma. One in three severe cases will be fatal, and most survivors experience significant brain damage.
There are no specific treatments for EEE. Victims should be immediately hospitalized, where they can receive fluids, respiratory support, and be protected from further infection.
Cache Valley Virus (CVV) Disease is rarely diagnosed, partly because laboratories rarely test for it. Its true effect on public health is yet to be determined. As of 2006, only two known cases were documented, a fatal case of acute encephalitis and a fully-recovered case of acute aseptic meningitis.
Like other arboviruses, CVV has no specific cure. The Wisconsin man who recovered fully from meningitis received antimicrobial drugs, corticosteroids, and pain medications. Most likely, the anti-inflammatory corticosteroids were the crucial treatment, preventing damaging swelling while CVV ran its course.
The Asian tiger mosquito is a potential vector of several other diseases, including Chikungunya fever, Japanese Encephalitis, La Crosse Encephalitis, St. Louis Encephalitis, and Western Equine Encephalitis. It also transmits canine heartworm.
As the temperate-zone diseases make clear, the most dangerous primary expression of arboviruses in humans is encephalitis and meningitis. Anyone experiencing disorientation, nausea, vomiting, or other telltale signs, should seek immediate medical attention.
* Diseases: Tropics *
1. Dengue fever
Although its cousin Aedes aegypti is the more common vector, the Asian tiger mosquito is a known vector of Dengue fever. Dengue is characterized by high fever, debilitating headaches, rash, and mild bleeding. Victims experience severe pain behind the eyes, and in joints, muscles, and bones. A more advanced form, called Dengue Hemorrhagic Fever (DHF), may set in after the initial fever declines. Symptoms of DHF include persistent vomiting, abdominal pain, and shortness of breath. Capillaries leak, which can cause a breakdown of the circulatory system, shock, and death.
There are no specific medications for Dengue or DHF. Those who believe they are infected should use pain relievers with acetaminophen and avoid aspirin. They should rest, stay hydrated, and consult a physician if possible. If vomiting begins after the fever declines, Dengue has likely progressed to DHF. Immediate hospitalization and fluid replacement therapy can prevent serious repercussions and death.
2. Yellow fever
Most yellow fever infections are mild, but severe cases are characterized by high fever, chills, headache, muscle aches, vomiting, and backache. These can be followed by shock, kidney failure, or liver failure. The jaundice associated with liver failure gives yellow fever its name.
Yellow fever is wholly preventable by vaccine. For those who have already contracted the illness, treatment is based on symptoms: rest, fluids, and pain and fever medications (excluding aspirin).
* Conclusions *
In the tropics, the Asian tiger mosquito is less of a threat than the related Aedes aegypti. Its true danger lies in temperate zones, where it is thriving and out-competing native mosquito species. It bites aggressively and during the day, when most people are outside and active.
Encephalitis and meningitis are the most severe conditions associated with arboviruses vectored by the Asian tiger mosquito. Anyone whose flu-like symptoms progress to confusion or loss of consciousness must be immediately hospitalized so the swelling can be treated before it causes permanent damage or death.
Arboviruses are most common in late summer and early fall, when mosquitoes carry the highest amounts of virus, and before cold weather causes most mosquitoes to die off. To limit your exposure, use insect repellent containing DEET, eliminate standing water where mosquitoes lay eggs, and wear long sleeved, loose-fitting clothes.
Centers for Disease Control and Prevention (http://www.cdc.gov/)
Cleveland Clinic (http://my.clevelandclinic.org/)
National Center for Biotechnology Information (http://www.ncbi.nlm.nih.gov/)