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Chikungunya Virus

Chikungunya virus is a positive single stranded RNA virus that is normally transmitted by Aedes mosquitoes, especially Aedes aegypti and Aedes albopictus which are common in the tropics, including urban areas. Human-to-mosquito-to-human infection occurs without the need for an intermediate amplifying host.

The virus is endemic in Africa, India, South­east Asia, and the Philippines. Large-scale outbreaks occurred during 2005-2007 in the Indian Ocean islands and then spread to several western India, Southeast Asia and northern Italy. An outbreak in the Caribbean that started in December 2013 has infected more than 100,000 people. The largest outbreak is in the Dominican Republic. A substantial number of imported cases have been docu­mented in the US and in European travelers returning from endemic areas. CDC reported that 25 cases have been confirmed in Florida. CDC is also monitoring cases, in Arkansas, California, Connecticut, Indiana, Maryland, Minnesota, Nebraska, Nevada, New York, North Carolina, Virginia, Puerto Rico and the U.S. Virgin Islands.

Incubation period is estimated to last from 3 to 12 days, without an obvious prodome. Viremia persists in most patients from 6 to 7 days. During this time, viral loads can range from 1.7 x 103 to 1.2 x 1010. Approximately 80% of infected individuals develop high fever, headache, myalgia and symmetrical joint pain in the wrists, elbows, fingers, knees and ankles. A pruritic, maculopapular rash occurs 4 to 8 days later with concurrent leukopenia. The acute febrile phase usually resolves after one week but incapacitating arthralgia may persist for months in 10 to 15% of people.

The defining clinical characteristic is extreme muscle and joint pain. The virus’ name is derived from a Swahili word that describes the extreme pain that people have as a result of the infection. No specific treatment or vaccine is available for chikungunya virus. Infection is thought to confer life-long immunity. Complications include meningoencephalitis, uveitis, retinitis, myocarditis, hepatitis, nephritis, bullous skin lesions, hemorrhage, myelitis, Guillain-Barré syndrome, and cranial nerve palsies. Vertical transmission has been reported including in utero infections, resulting in fetal deaths, and perinatal infection causing symptomatic disease in neonates.

An outbreak of a modified strain of Chikungunya virus on La Réunion Island in the Indian Ocean between September, 2005 and June, 2006 resulted in 57 cases of encephalitis. This was a highly significant outbreak of a modified strain with more serious outcomes than previous outbreaks of the virus.

Even though no transfusion transmitted cases have been confirmed, the risk for transmission by blood transfusion is theoretically high because at least 20% of infected individuals may be asymptomatic and high titer viremia can last for approximately a week. There are no current standards on donor deferral periods during a chikungunya outbreak, donor screening questions, or licensed screening tests. Since the outbreak is likely to spread, however, the transfusion community needs to be prepared.

Diagnostic tests include virus isolation from blood, RT-PCR to detect circulating virus and serologic tests to detect IgG and/or IgM-specific antibody by indirect immunofluorescence or enzyme immunoassay. The diagnostic strategy is twofold. If a serum specimen is obtained 1 to 7 days after the onset of symptoms, real-time PCR can be used to detect viral genome. Real-time PCR testing can differentiate between Dengue virus and Chikungunya. Unfortunately, some infected persons seek medical care at a time when real-time PCR is no longer effective for diagnosis. If serum is collected more than 5 days after onset of symptoms, serologic techniques are used to detect IgM and/or IgG responses to the virus. Specimens collected too early following infection may be negative for antibodies to Chikungunya virus. Testing of convalescent serum is recommended to confirm the diagnosis.

Commercially available ELISAs have very poor sensitivity and specificity (Prat C. etal. Emerging Infectious Diseases, Volume 20, Number 12—December 2014). Specimens should preferably be sent to a reference laboratory. As of July 2015, Focus Diagnostics was the only commercial lab offering PCR and serologic testing.

Chikungunya and Dengue viruses share the same endemic area and infections with these viruses may present with similar clinical symptoms. Testing for both viruses at the initial presentation may expedite diagnosis.

Reference values are negative results for both Chikungunya virus IgG and IgM. Specimen requirement for serologic testing is a red top tube of blood.

Reference value for Chikungunya RNA PCR is not detected. Specimen requirement is a red top tube of blood.

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