Signs and symptoms Edit
The incubation period of the chikungunya virus ranges from one to twelve days, and is most typically three to seven.[12] The disease may be asymptomatic, but generally is not, as 72% to 97% of those infected will develop symptoms.[12] Characteristic symptoms include sudden onset with high fever, joint pain, and rash. Other symptoms may occur, including headache, fatigue, digestive complaints, and conjunctivitis.[2]
Information gained during recent epidemics suggests that chikungunya fever may result in a chronic phase as well as the phase of acute illness.[13] Within the acute phase, two stages have been identified: a viral stage during the first five to seven days, during which viremia occurs,[14] followed by a convalescent stage lasting approximately ten days, during which symptoms improve and the virus cannot be detected in the blood.[12] Typically, the disease begins with a sudden high fever that lasts from a few days to a week, and sometimes up to ten days. The fever is usually above 39 °C (102 °F) and sometimes reaching 40 °C (104 °F) and may be biphasic—lasting several days, breaking, and then returning. Fever occurs with the onset of viremia, and the level of virus in the blood correlates with the intensity of symptoms in the acute phase.[14] When IgM, an antibody that is a response to the initial exposure to an antigen, appears in the blood, viremia begins to diminish. However, headache, insomnia and an extreme degree of exhaustion remain, usually about five to seven days.[15]
Following the fever, strong joint pain or stiffness occurs; it usually lasts weeks or months, but may last for years. The joint pain can be debilitating, often resulting in near immobility of the affected joints.[16] Joint pain is reported in 87–98% of cases, and nearly always occurs in more than one joint, though joint swelling is uncommon.[12] Typically the affected joints are located in both arms and legs, and are affected symmetrically. Joints are more likely to be affected if they have been previously been damaged by disorders such as arthritis.[13] Pain most commonly occurs in peripheral joints, such as the wrists, ankles, and joints of the hands and feet as well as some of the larger joints, typically the shoulders, elbows and knees.[12][13] Pain may also occur in the muscles or ligaments.
Rash occurs in 40-50% of cases, generally as a maculopapular rash occurring two to five days after onset of symptoms.[12] Digestive symptoms, including abdominal pain, nausea, vomiting or diarrhea, may also occur.[2][12][17] In more than half of cases, normal activity is limited by significant fatigue and pain.[12] Infrequently, inflammation of the eyes may occur in the form of iridocyclitis, or uveitis, and retinal lesions may occur.[18]
Rarely, neurological disorders have been reported in association with chickungunya virus, including Guillain-Barré syndrome, palsies, meningoencephalitis, flaccid paralysis and neuropathy.[2] In contrast to dengue fever, Chikungunya fever very rarely causes hemorrhagic complications. Symptoms of bleeding should lead to consideration of alternative diagnoses or co-infection with dengue fever or coexisting congestive hepatopathy.[14]
Chronic disease Edit
Observations during recent epidemics have suggested chikungunya may cause long-term symptoms following acute infection.[19][20][21] This condition has been termed chronic chickungunya virus-induced arthralgia.[10] Long-term symptoms are not an entirely new observation; long-term arthritis was observed following an outbreak in 1979.[22] Common predictors of prolonged symptoms are increased age and prior rheumatological disease.[4][23][24][25]
During the La Reunion outbreak in 2006, more than 50% of subjects over the age of 45 reported long-term musculoskeletal pain[23] with up to 60% of people reporting prolonged painful joints three years following initial infection.[4] A study of imported cases in France reported that 59% of people still suffered from arthralgia two years after acute infection.[26] Following a local epidemic of chikungunya in Italy, 66% of people reported muscle pains, joint pains, or asthenia at one year after acute infection.[24]
Currently, the cause of these chronic symptoms is not fully known. Markers of autoimmune or rheumatoid disease have not been found in people reporting chronic symptoms.[4][27] However, some evidence from humans and animal models suggests chikungunya may be able to establish chronic infections within the host. Viral antigen was detected in a muscle biopsy of a person suffering a recurrent episode of disease three months after initial onset.[28] Additionally, viral antigen and viral RNA were found in macrophages in the synovial joint of a person experiencing a relapse of musculoskeletal disease 18 months after initial infection.[29] Several animal models have also suggested chikungunya virus may establish persistent infections. In a mouse model, viral RNA was detected specifically in joint-associated tissue for at least 16 weeks after inoculation, and was associated with chronic synovitis.[30] Similarly, another study reported detection of a viral reporter gene in joint tissue of mice for weeks after inoculation.[31] In a nonhuman primate model, chikungunya virus was found to persist in the spleen for at least six weeks.[32]