Diagnosis of Chikungunya
Chikungunya infections can be confirmed by the detection of the virus, viral RNA, or specific antibodies in patient samples. The type of testing performed is typically dictated by the timing and volume of samples available. Blood test is the only reliable way to identify chikungunya since the symptoms are similar to much more deadly dengue fever. Common laboratory tests for chikungunya include for instance RT-PCR and serological tests.
Viral RNA can be easily detected by reverse transcriptase-polymerase chain reaction (RT-PCR) in serum specimens obtained from patients during the acute phase of infection. Chikungunya infections cause high levels of viremia (up to 1x10E6.8 plaque-forming units per mL), which typically last for 4–6 days after the onset of illness. RT-PCR can therefore easily been done within the first 7 days on an acute-phase specimen to confirm chikungunya virus infection. RT–PCR products from clinical samples may also be used for genotyping of the virus, allowing comparisons with virus samples from various geographical sources. PCR results can be available within one to two days.
Enzyme-linked immunosorbent assays (ELISA) detect both anti-CHIKV immunoglobulin (Ig) M and IgG antibodies from either acute- or convalescent-phase samples. Serological diagnosis requires a larger amount of blood than the other methods. ELISA results require 2–3 days and the test is quite specific with very little cross reactivity with related alphaviruses. Testing of samples from imported cases found that chikungunya-specific IgM antibodies develop rapidly within a few days after illness onset and persist for several months.
Immunofluorescence assays are sensitive and specific but lack the ability to quantify antibodies, are subjective, and require special equipment and training. However, these tests are commercially available and are an option for laboratories that routinely use this method for detection of other infectious agents.
Plaque reduction neutralization tests (PRNT) are very useful because they are quite specific for alphaviruses and are the gold standard for confirmation of serologic test results. The major drawback to PRNT is that it requires the use of live virus. The test must be carried out in Biosafety level 3 laboratories (BSL-3) that requires special laboratory containment equipments.
Another way to diagnose the disease is by distinguishing the chikungunya strain by kinetic Haemagglutination-inhibition tests. Chikungunya is confirmed when symptoms such as fever and joint pain seen along with a four fold Haemagglutination Inhibition antibody difference in paired serum samples. This turns positive within 5 to 8 days of infection.
Testing of both acute- and convalescent-phase samples, collected at least 3 weeks apart, from a patient presenting with a high fever combined with severe joint pain and recent travel to a chikungunya outbreak area should be sufficient to confirm the infection. However, cryoglobulinemia has recently been reported in several patients. Therefore, if a patient presents with appropriate clinical syndrome and travel to an affected area, this should be considered if serologic test results are negative. Health care providers should contact their state or local health department or the CDC for assistance with diagnostic testing.
Dengue and Chikungunya: Making the Diagnosis Chikungunya fever is somewhat similar to the fever of dengue. Chikungunya and dengue are both acute febrile illnesses characterized by fever, myalgia, and lethargy. Some patients may also have maculopapular rash, nausea, vomiting, and headache. Distinguishing features of chikungunya include potentially debilitating bilateral polyarthralgia and, in some cases, arthritis. Although these signs and symptoms may assist in differentiating dengue and chikungunya, clinicians should include both illnesses in their differential diagnosis of patients with acute febrile illness and recent travel to the tropics. The CDC has a comprehensive expert opinion on differentiating chikungunya from dengue: a clinical challenge (Medscape, 14 September 2014).