Chapter 4 Travel-Related Infectious Diseases
J. Erin Staples, Susan L. Hills, Ann M. Powers
Chikungunya virus is a single-stranded RNA virus that belongs to the family Togaviridae, genus Alphavirus.
Chikungunya virus is transmitted to humans via the bite of an infected mosquito of the Aedes spp., predominantly Aedes aegypti and Ae. albopictus. Mosquitoes become infected when they feed on viremic nonhuman or human primates, which are likely the main amplifying reservoirs of the virus. Humans are typically viremic shortly before and in the first 2–6 days of illness. Bloodborne transmission is possible; 1 case has been documented in a health care worker who was stuck with a needle after drawing blood from an infected patient. Furthermore, chikungunya virus has been identified in donated blood products undergoing screening, though no transfusion-associated cases have been identified to date. Cases have also been documented among laboratory personnel handling infected blood and through aerosol exposure in the laboratory. Maternal–fetal transmission has been documented during pregnancy; the highest risk occurs in the perinatal period when a woman is viremic at the time of delivery. Studies have not found virus in breast milk.
Chikungunya virus often causes large outbreaks with high attack rates, affecting one-third to three-quarters of the population in areas where the virus is circulating. Outbreaks of chikungunya have occurred in Africa, Asia, Europe, the Americas, and islands in the Indian and Pacific Oceans. In late 2013, the first locally acquired cases of chikungunya were reported in the Americas on islands in the Caribbean. By the end of 2017, more than 2.6 million suspect cases of chikungunya had been reported in the Americas. Since then, the virus has continued to circulate and cause sporadic disease cases and periodic outbreaks in many areas of the world.
Risk to travelers is highest in 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 near human habitation served as vector-breeding sites. Risk of infection exists primarily during the day, as the primary vector, Ae. aegypti, aggressively bites during the daytime. Ae. aegypti mosquitoes bite indoors or outdoors near dwellings. They lay their eggs in domestic containers that hold water, including buckets and flowerpots.
Both adults and children can become infected and symptomatic with the disease. From 2010 through 2013, 110 cases of chikungunya were identified or reported among US travelers, who predominantly traveled to areas with known ongoing outbreaks. However, following the outbreaks in the Americas, from 2014–2017, >4,000 chikungunya cases were reported among US travelers, and 13 locally acquired cases were reported in the continental United States. In addition, US territories (Puerto Rico, US Virgin Islands, and American Samoa) reported locally acquired cases during 2014–2015, with Puerto Rico also reporting sporadic cases since 2016.
Characteristics of chikungunya and other arboviral diseases are shown in Box 4-01.
Approximately 3%–28% of people infected with chikungunya virus will remain asymptomatic. For people who develop symptomatic illness, the incubation period is typically 3–7 days (range, 1–12 days). Disease is most often characterized by sudden onset of high fever (temperature typically >102°F [39°C]) and joint pains. Other symptoms may include headache, myalgia, arthritis, conjunctivitis, nausea, vomiting, or a maculopapular rash. Fevers typically last from several days up to 1 week; the fever can be biphasic. Joint symptoms are typically severe and can be debilitating. They usually involve multiple joints, typically bilateral and symmetric. The joint pains occur most commonly in hands and feet, but they can affect more proximal joints. Rash usually occurs after onset of fever. It typically involves the trunk and extremities but also can include the palms, soles, and face.
Abnormal laboratory findings can include thrombocytopenia, lymphopenia, and elevated creatinine and liver function tests. Rare but serious complications of the disease can occur, including myocarditis, ocular disease (uveitis, retinitis), hepatitis, acute renal disease, severe bullous lesions, and neurologic disease, such as meningoencephalitis, Guillain-Barré syndrome, myelitis, or cranial nerve palsies. Groups identified as having increased risk for more severe disease include neonates exposed intrapartum, adults >65 years of age, and people with underlying medical conditions, such as hypertension, diabetes, or heart disease.
Acute symptoms of chikungunya typically resolve in 7–10 days. Fatalities associated with infection occur but are rare and most commonly reported in older adults and those with comorbidities. Some patients will have a relapse of rheumatologic symptoms such as polyarthralgia, polyarthritis, tenosynovitis, or Raynaud syndrome in the months after acute illness. Studies have reported variable proportions, ranging from 5% to 80%, of patients with persistent joint pains, as well as prolonged fatigue, for months or years after their illness.
Pregnant women have symptoms and outcomes similar to those of other people, and most infections that occur during pregnancy will not result in the virus being transmitted to the fetus. However, intrapartum transmission can result in neonatal complications, including neurologic disease, hemorrhagic symptoms, and myocardial disease. There are also rare reports of spontaneous abortions after maternal infection during the first trimester.
The differential diagnosis of chikungunya virus infection depends on the clinical signs and symptoms as well as where the person was suspected of being infected. Diseases that should be considered in the differential diagnosis include dengue, Zika, malaria, leptospirosis, parvovirus, enterovirus, group A Streptococcus, rubella, measles, adenovirus, postinfectious arthritis, rheumatologic conditions, or alphavirus infections (including Mayaro, Ross River, Barmah Forest, o’nyong’nyong, and Sindbis viruses).
Preliminary diagnosis is based on the patient’s clinical features, places and dates of travel, and exposures. 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, chikungunya can often be diagnosed by performing viral culture or nucleic acid amplification on serum. Virus-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 chikungunya virus is performed at several state health department laboratories and commercial laboratories. Confirmatory testing for virus-specific neutralizing antibodies is available through CDC (Division of Vector-borne Diseases, 970-221-6400). Health care providers should report suspected chikungunya cases to their state or local health departments to facilitate diagnosis and mitigate the risk of local transmission. Because chikungunya is a nationally notifiable disease, state health departments should report laboratory-confirmed cases to CDC through ArboNET, the national surveillance system for arboviral diseases.
No specific antiviral treatment is available for chikungunya; however, a number of therapeutic options are being investigated. Treatment for symptoms can include rest, fluids, and use of analgesics and antipyretics. Nonsteroidal anti-inflammatory drugs can be used to help with acute fever and pain. In dengue-endemic areas, however, acetaminophen is the preferred first-line treatment for fever and joint pain until dengue can be ruled out, to reduce the risk of hemorrhage. For patients with persistent joint pain, use of nonsteroidal anti-inflammatory drugs, corticosteroids including topical preparations, and physical therapy may help lessen the symptoms.
Currently, no vaccine or preventive drug is available. However, several candidate vaccines are in various stages of development. The best way to prevent infection is to avoid mosquito bites (see Chapter 3, Mosquitoes, Ticks & Other Arthropods). Travelers at increased risk for more severe disease, including travelers with underlying medical conditions and women who are late in their pregnancy (as their fetuses are at increased risk), may consider avoiding travel to areas with ongoing outbreaks. If travel is unavoidable, emphasize the need for protective measures against mosquito bites.
CDC website: www.cdc.gov/chikungunya
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