Viral diseases transmitted by mosquitoes have been recognized for many years as a public health problem. It is not unusual for people visiting countries with a high prevalence of a mosquito-transmitted viral disease to return home ill. Because of immigration and travel to and from South America, health care providers are beginning to encounter infections rarely or never previously seen in the U.S.

Mosquitoes are capable of transmitting a number of parasitic (e.g. malaria) and viral diseases.

Zika virus

On February 1, 2016 the World Health Organization declared the Zika virus a public health emergency for the Americas. This concern has also been supported by the Centers for Disease Control (CDC). The primary concern of this infection is that it can cause serious birth defects if the infection occurs in early pregnancy and is associated with other neurological conditions.

This virus was first recognized in 2008 but was rare. In May 2015, this infection was described in Brazil, and by December 2015, the first local transmission of Zika virus infection was reported in the Caribbean. Since then, Caribbean destinations reporting ongoing transmission of Zika have been Barbados, Dominican Republic, Guadeloupe, Saint Martin and the U.S. Virgin Islands.

According to the CDC, about one in five people infected with Zika virus become symptomatic. Symptoms include sudden onset of fever, rash, joint pain, or eye irritation. Clinical illness usually is mild with symptoms lasting for several days to a week. Severe disease requiring hospitalization is uncommon and fatalities are rare. During the current outbreak in Brazil, Zika virus was found in tissues from infants with microcephaly (underdevelopment of the brain) and from fetal losses in women infected during pregnancy. The virus can also be spread through the semen of an infected male.

The CDC has issued travel information about South American and Caribbean countries (see sidebar). The basic recommendation is that women who are pregnant or planning to become pregnant should postpone travel to South and Central America and the Caribbean until better information is available. At present there is a blood test to detect Zika virus, but no vaccine or treatment.

Chikungunya virus

Chikungunya (pronunciation: (chik-en-gun-ye) outbreaks have occurred in Africa, Asia, Europe, and the Indian and Pacific Oceans. In late 2013, chikungunya virus was found for the first time in the Americas on islands in the Caribbean. There is a risk that the virus will be imported to new areas by infected travelers. There is no vaccine to prevent or medicine to treat chikungunya virus infection.

Symptoms typically resolve within seven to 10 days. Rare complications include eye problems, heart muscle inflammation, hepatitis, kidney inflammation, blistering skin lesions, meningitis, muscle inflammation, Guillain-Barré syndrome and facial nerve paralysis. Persons at risk for severe disease include newborns exposed before birth, older adults (e.g., > 65 years), and persons with underlying medical conditions. Some adults experience arthritis symptoms that can lead to chronic joint pain. Mortality is rare and occurs mostly in older adults.

Dengue

Although dengue rarely occurs in the continental United States, it is endemic in Puerto Rico and in many popular tourist destinations in Latin America, Southeast Asia and the Pacific islands. With more than one-third of the world’s population living in areas at risk for infection, dengue virus is a leading cause of illness and death in the tropics and subtropics. As many as 400 million people are infected yearly. Dengue is caused by any one of four related viruses transmitted by mosquitoes. Signs and symptoms of dengue include high fever up to 106 F, headache, muscle and joint pain and pain behind the eyes. There is also rash, nausea and vomiting and bleeding from nose and mouth.

There is no vaccine to prevent infection with dengue virus, and the most effective protective measures are actions to avoid mosquito bites. They include wearing long-sleeved shirts and pants during the time of day that mosquitoes are the most active, using DEET sprays, and avoiding use of perfumes and colognes that attract insects.

Seek out medical care early if any unusual symptoms develop when traveling or on return home. When infected, early recognition and prompt supportive treatment can substantially lower the risk of medical complications and death.

Information for travelers

• Avoid bug bites: http://www.cdc.gov/travel/page/avoid-bug-bites)

• Center for Disease Control zika website: http://cdc.gov/zika

• Zika virus in Central America: wwwnc.cdc.gov/travel/notices/watch/zika-virus-central-america)

• Zika virus in Mexico: wwwnc.cdc.gov/travel/notices/watch/zika-virus-mexico)

• Zika virus in South America: wwwnc.cdc.gov/travel/notices/watch/zika-virus-south-america)