Chapter 3Infectious Diseases Related To Travel
J. Erin Staples, Susan L. Hills, Ann M. Powers
Infection is caused by the chikungunya virus (CHIKV), a single-stranded RNA virus that belongs to the family Togaviridae, genus Alphavirus.
MODE OF TRANSMISSION
Transmission occurs via the bite of an infected mosquito of the Aedes spp., predominantly Aedes aegypti and Ae. albopictus. Nonhuman and human primates are likely the main reservoirs of the virus with anthroponotic (human-to-vector-to-human) transmission occurring during outbreaks of the disease. Bloodborne transmission is possible; cases have been documented among laboratory personnel handling infected blood and a health care worker drawing blood from an infected patient.
The risk of a person transmitting the virus to a biting mosquito or through blood is highest when the patient is viremic during the first 2–6 days of illness. Maternal-fetal transmission has been documented during pregnancy. The highest risk occurs when a woman is viremic at the time of delivery, with a vertical transmission rate of 49%. CHIKV does not appear to be transmitted through breast milk.
CHIKV has been identified in many countries in Africa and Asia and is responsible for numerous epidemics in these areas. Since the disease reemerged in 2004, millions of cases have occurred and continue to occur throughout countries in and around the Indian Ocean. Transmission has also been documented periodically in temperate areas, such as in Italy in 2007. Given the large CHIKV epidemics, high level of viremia in humans, and the worldwide distribution of Ae. aegypti and Ae. albopictus, there is a risk of importation of chikungunya virus into new areas by infected travelers.
Risk for travelers is highest with travel to areas experiencing ongoing epidemics of the disease. Most epidemics occur during the tropical rainy season and abate during the dry season. However, outbreaks in Africa have occurred after periods of drought, where open water containers served as vector-breeding sites. Risk of CHIKV infection exists throughout the day, as the primary vector, Ae. aegypti, aggressively bites during the daytime. Ae. aegypti mosquitoes bite indoors or outdoors near a dwelling. They typically breed in domestic containers that hold water, including buckets and flower pots.
Both adults and children can become infected and symptomatic with the disease. From 2006 through 2009, 105 cases of chikungunya fever were identified among US travelers. Most cases were travelers returning from areas with ongoing disease activity.
Approximately 3%–28% of people infected with CHIKV will remain asymptomatic. For people who develop symptomatic illness, the incubation period is typically 3–7 days (range, 2–12 days). Disease is most often characterized by sudden onset of high fever (temperature typically higher than 39°C [102°F]) and severe joint pain or stiffness. Other symptoms may include rash, headache, fatigue, nausea, vomiting, and myalgias. Fevers typically last from several days up to 1 week; the fever can be biphasic. Joint symptoms are severe and often debilitating. They are usually symmetric and occur most commonly in hands and feet, but they can affect more proximal joints. Rash usually occurs after onset of fever. It is typically maculopapular, involving the trunk and extremities, but can also include palms, soles, and face.
Abnormal laboratory findings can include thrombocytopenia, leukopenia, and elevated liver function tests. Rare but serious complications of the disease can occur, including myocarditis, ocular disease (uveitis, retinitis), hepatitis, acute renal disease, severe bulbous lesions, and neuroinvasive disease, such as meningoencephalitis, Guillain-Barré syndrome, paresis, or palsies. Fatalities related to CHIKV infection are rare. Older age and comorbidities are likely risk factors for poor outcomes.
After the acute illness, some patients have prolonged fatigue lasting several weeks. Additionally, some patients have reported incapacitating joint pain, stiffness, or tenosynovitis, which may last for weeks or months. Some studies have reported joint symptoms more than a year after the initial infection.
Pregnant women have symptoms and outcomes similar to those of other people, and most CHIKV infections that occur during pregnancy will not result in the virus being transmitted to the fetus. However, when intrapartum transmission occurs, it can result in complications for the baby, including neurologic disease, hemorrhagic symptoms, and myocardial disease. There are also rare reports of spontaneous abortions after maternal CHIKV infection.
Preliminary diagnosis is based on the patient’s clinical features, places and dates of travel, and activities. Laboratory diagnosis is generally accomplished by testing serum to detect virus, viral nucleic acid, or virus-specific IgM and neutralizing antibodies. During the first week after onset of symptoms, CHIKV infection can often be diagnosed by using viral culture or nucleic acid amplification on serum. CHIKV-specific IgM and neutralizing antibodies normally develop toward the end of the first week of illness. Therefore, to definitively rule out the diagnosis, convalescent-phase samples should be obtained from patients whose acute-phase samples test negative.
Testing for CHIKV IgM and IgG is commercially available. However, confirmatory neutralizing antibody testing is only available through CDC (970-221-6400) and a few state health laboratories. Although reporting CHIKV infections is not mandatory in the United States, all clinicians are encouraged to notify their state or local health department of suspected CHIKV cases to mitigate the risk of local (anthroponotic) transmission.
No specific antiviral treatment is available for chikungunya fever. Treatment is for symptoms and can include rest, fluids, and use of analgesics and antipyretics. Infected people should be protected from further mosquito exposure (staying indoors in areas with screens or under a mosquito net) during the first few days of the illness, so they do not contribute to the transmission cycle.
PREVENTIVE MEASURES FOR TRAVELERS
No vaccine or preventive drug is available. Caution should be used when advising travelers at increased risk for more severe disease, including travelers with significant comorbidities and pregnant women whose unborn infants are at increased risk, about travel to areas with ongoing outbreaks of the disease. The best way to prevent chikungunya virus infection is to avoid mosquito bites (see Chapter 2, Protection against Mosquitoes, Ticks, and Other Insects and Arthropods).
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