Barmah Forest (BF) virus infection occurs when the virus is transmitted to humans through a mosquito bite. Mosquitoes become carriers (vectors) when they feed on an animal infected with the virus, often a kangaroo or wallaby. The virus is indigenous to Australia.
Persons infected with Barmah Forest virus may be asymptomatic or may experience flu-like symptoms. Children are often asymptomatic or present with milder symptoms that usually appear for a short duration in comparison to adults . Symptoms typically onset 1 to 2 weeks after being bitten by an infected mosquito carrying the virus. The most common clinical features of the disease include polyarthritis, arthralgia, myalgia, malaise, and low-grade fever  . Joints that are often affected include the jaw, wrists, elbows, shoulders, knees, and ankles. Joints are usually painful, rather than swollen. Other, less common, symptoms include joint swelling, muscle aches and soreness, vesicular rash, headaches, lymphadenopathy, extreme fatigue, nausea, discomfort around the eyes and orbital area, sore throat, tingling in the palms or soles of the feet . Signs and symptoms typically remit 2 to 6 weeks after infection but have been reported to last as long as one year or more (long-term symptoms will often wax and wane). Anxiety, emotional distress, depression, and disruption of daily activities of life may occur in individuals that have the long-term disease.
Diagnosis of Barmah Forest virus infection is based on clinical presentation and serological testing. Workup begins with a history and physical exam. Patients should be asked about any recent travel to Australia in particular, or to other developing countries worldwide. Rashes or skin lesions indicative of a mosquito bite may be identified during the physical exam. Routine laboratory testing (e.g., serum chemistry, hematology testing including complete blood count with differential count) and radiology tests are usually unaltered by the viral infection and therefore are not useful for the diagnosis of Barmah Forest virus. A definitive diagnosis is achieved through serology tests, in particular, the observation of increasing immunoglobulin (Ig) G levels .
Many of the clinical features of Barmah Forest virus are similar to those of Ross River virus disease . Diagnosis and differentiation of the two diseases can only be confirmed through serological testing (specifically, the measurement of antibodies, IgM, and IgG levels) .
Serological tests include:
Less common (and less readily available) tests that may be performed to facilitate diagnosis include testing for Barmah Forest virus nucleic acid (RNA), isolation of the virus itself , and microneutralization antibody test .
All of the aforementioned tests provide a clear distinction between infections with alphaviruses, including Barmah Forest virus.
The clinician should keep in mind that antibodies to the Barmah Forest virus may remain detectable for up to 4 years after infection . Additionally, false positive results may occur in patients with comorbidities such as autoimmune disease.