Zika Virus, Other Mosquito-Borne Illnesses, and Mobile Populations

Zika virus disease (Zika) is the result of an infection from the Zika virus, which can be contracted from the bite of an infected Aedes mosquito. Intrauterine or perinatal and sexual transmission may also occur. Additionally, a patient may contract the virus after a blood transfusion from an infected donor. Within two weeks of exposure, a patient infected with Zika may present fever, rash, joint pain, and conjunctivitis, for several days to one week, but an estimated 80 percent of infected people are asymptomatic.

Reporting and preventative literature on Zika has been heavily focused on pregnant women. Zika virus infection during pregnancy increases the risk of microcephaly, a serious birth defect, as well as other severe fetal brain defects.  In areas like Brazil where there has been an increase in microcephaly, the incidence of microcephaly among fetuses with congenital Zika infection is still unknown.  

In a small percentage of cases, Zika may result in Guillain-Barre Syndrome (GBS), in which the immune system damages nerve cells, causing muscle weakness and possible paralysis.  While many patients recover from the syndrome in a matter of months, some have permanent nerve damage. One in 20 cases of GBS results in death.

Before 2015, Zika had been limited to Africa, Southeast Asia, and the Pacific Islands. In 2015, Zika spread rapidly in South America, Central America, Mexico, and the Caribbean. Because the Aedes mosquito -- the primary transmitter of Zika -- lives in many areas of the United States, it is possible that the virus may spread into Eastern, Southern, Southwestern, and Western regions of the US.  As of this writing, local mosquito-borne transmission in the US has been limited to Florida and Texas.  Visit the CDC's Areas with Zika website to learn where there is current transmission.

Migrant Patients: Risks and Diagnosis

Many immigrants to the US arrive from South America, Central America, the Caribbean, and Mexico, areas that are currently experiencing Zika outbreaks, in addition to the hundreds of migrants from Puerto Rico to the mainland US. Education and awareness may be limited in migrant populations, who due to their mobility may have missed opportunities to learn about the virus in their communities. Additionally, migrants may not be in a position to obtain timely care. 

Because migrant clinicians serve a population that is on the move, any clinician serving migrants or newly arrived immigrants should determine whether the patient had recently traveled to an area experiencing a Zika outbreak OR if the patient intends on moving to such an area in the future.

Travelers coming from Zika outbreak areas may spread the virus into new areas. Any patients who are pregnant and have traveled to areas with Zika while pregnant should be evaluated, and given information on the risks of exposure and the need for ongoing evaluation. Any patients presenting the aforementioned symptoms within two weeks of traveling to an infected area should undergo serum testing. Zika symptoms are similar to those of dengue and chikungunya, and the diseases are often found in the same area (as they are spread by the same type of mosquitoes). The CDC notes that it is important to rule out dengue, as proper clinical management can improve outcome.

The Food and Drug Administration (FDA) has issued an Emergency Use Authorization (EUA) for two diagnostic tools: the Zika MAC-ELISA and Trioplex real-time reverse transcription-polymerase chain reaction (rRT-PCR) Assay. The CDC requests that clinicians contact their state or local health department to facilitate testing. Read the CDC’s full instructions for sending diagnostic specimens for more information on diagnostic testing.

Patients who intend to travel to areas of Zika outbreak should be aware of the risks.  All migrant women of childbearing age should be asked about their recent and future travel plans. All migrant women who are pregnant or considering pregnancy should be encouraged to delay travel to areas with a Zika outbreak if possible. Resources, including fact sheets for pregnant women and a preconception counseling guide, are available from the CDC in English and Spanish.

For more on diagnostic testing, treatment, and evaluation, along with tools and resources for health care providers, visit the CDC’s Zika Virus for Healthcare Providers, which includes archives of webinars on Zika for clinicians, like this one from January 2016.

Outdoor workers like agricultural workers are more likely to contract Zika because of the greater risk of mosquito bites. The Occupational Safety and Health Administration (OSHA), in cooperation with the CDC, outlined top actions that both employers and workers can take to prevent mosquito bites and reduce mosquito presence in outdoor work situations, in their Interim Guidance for Protecting Workers from Occupational Exposure to Zika Virus. Key takeaways include the importance of education, prevention through removal of standing water and use of lightweight but long-sleeved clothing, and proper use of approved insect repellants.

Workers in health care settings and laboratories should follow good infection control and biosafety practices (including universal precautions for BBP exposure) as appropriate, to prevent or minimize the risk of transmission of infectious agents like Zika. Standard precautions can be used to expand the universal precautions required by the BBP standard by adding several protections such as hand hygiene and the use of PPE to avoid direct contact with blood and other potentially infectious materials, including laboratory specimens/samples. PPE may include gloves, gowns, masks and eye protection.

Migrant housing is often substandard. Clinicians may seek to educate patients on the importance of screened windows and doors.  Clinicians may also educate patients about community-based approaches to mosquito breeding ground elimination, including the draining of stagnant water in their own yards. Personal empowerment and a mobilized community are critically important ways to lower mosquito presence and prevent mosquito-borne illnesses from spreading. Residents, outdoor businesses, and outdoor workers can make a significant difference by emptying out standing water which may harbor mosquito larvae in places like old tires, gutters, vases, buckets, pet dishes, trash containers, and rain barrels.

Chikungunya is a viral disease spread by Aedes mosquitoes. The most common symptoms are sudden fever and joint pain, but the virus may also cause rash, muscle pain, nausea, headache, or fatigue. The word “chikungunya” comes from the Kimakonde language in Tanzania, and describes the contorted figure of an infected patient, as chikungunya is marked by arthralgia, which may last a few days or in some cases may linger for weeks or even months. Serious long-term complications include encephalitis but are uncommon, and most patients are expected to fully recover. Serological and virological testing should be done to confirm diagnosis, as the illness mimics that of Zika and dengue. (Read more about diagnosis on the WHO’s chikungunya fact sheet.) There is no cure for chikungunya, and treatment is primarily directed at reducing discomfort in the patient. Chikungunya has recently been listed as a nationally notifiable disease in the US.

Chikungunya has long been found in Asia and Africa, but the virus was first noted in the Americas in December 2013, when it jumped from Southeast Asia to the island of St. Martin. It spread quickly throughout Central America and the Caribbean by infected Aedes mosquitoes. Puerto Rico recorded its first case in May, 2014; by the end of that year, it had tallied over 20,000 suspected cases. The island saw fewer cases in 2015. There have been isolated cases in the mainland US as well. In 2014, 12 patients contracted chikungunya from mosquitoes in Florida, but none in 2015. In 2016, the first locally-transmitted case of chikungunya was confirmed by the CDC in Texas. Unlike previous cases in Texas, this patient had not traveled to areas of outbreak. The CDC confirmed the transmission over six months after the patient contracted the virus, and local mosquito testing has not uncovered infected local mosquitoes. Consequently, precautions continue to be generally focused on travelers to areas of active outbreak.

An estimated 100 million cases of dengue occur each year. Dengue is found in tropical regions around the world, including Hawaii and Florida, Mexico, the Caribbean including Puerto Rico, and Central America. The four closely related viruses that are called dengue are transmitted only by Aedes mosquitoes. In a small percentage of cases, a dengue infection may result in Dengue Hemorrhagic Fever, in which the patient has a fever lasting from two to seven days, followed by a one- to two-day period during which the capillaries throughout the body become permeable, causing circulatory system failure. DHF can be deadly if not properly treated.

The World Health Organization noted that 2015 was a year of dengue outbreaks throughout the world, including 1.5 million cases in Brazil, 169,000 cases in the Philippines, 111,000 in Malaysia, and other large outbreaks in India, Hawaii and other Pacific islands.

In December 2015, Mexico became the first country to approve a new vaccine against dengue, called Dengvaxia. As of July 2016, five other countries have followed suit. The vaccine is for use in individuals aged 9 to 45 living in endemic areas and studies are underway to determine its efficacy. A WHO Vaccine Position Paper is expected soon.

West Nile is another virus primarily spread by mosquitoes. West Nile was first identified in the mainland US in 1999, was quickly detected in mosquito populations across all states, and has since spread to Canada, the Caribbean, Mexico, Central America, and elsewhere. Unlike the other viruses highlighted on this page, West Nile is carried by a large variety of mosquito species. In about 20 percent of cases, patients infected with West Nile experience fever accompanied by headache, joint ache, vomiting, diarrhea or rash. Many individuals infected with West Nile have no symptoms at all. In less than one percent of cases, West Nile can advance to encephalitis or meningitis, particularly among young children, people over 60, and immunocompromised patients. No vaccine currently exists.