Chikungunya is caused by the alpha virus. The mosquitoe taking part in the infection of the disease is through Aedes aegypti, Aedes albopictus
Alpha viruses RNA enveloped virus belonging to Toga viridae family.They are mostly mosquitoe borne.The virus mainly affects the brain.Types of the Virus include. 1) eastern equine encephalomyelitis (EEE); 2) Venezuelan equine encephalomyelitis (VEE); and 3) western equine encephalomyelitis (WEE).They are atypical arboviruses and the pathogens include Chikunkunya and other encephalitis causing virus
Alpha viruses small ,single stranded ,enveloped virus.There are two frames in the genome which are termed as Structural Proteins and Non Structural proteins.The non structure proteins aid the virus in the transcription and replication of the viral DNA.The structural protein helps the virus to build the framework such as Core,nucleocapsid and plays a vital role in the receptor recognization and helps the virus to bind with the host
Alphaviruses enter cells by receptor-mediated endocytosis and exit by budding from the plasma membrane.
Alphaviruses enter the body via mosquito bites and replicate in various tissues, including Langerhans cells, which then migrate to lymph nodes, causing viremia. Viremia results in invasion of the central nervous system (CNS) by alphaviruses that cause encephalitis or of the joints and internal organs by viruses that cause fever, arthralgia, and rash.
All alphaviruses suppress the innate immune response by inhibiting JAK/STAT signaling, a major early determinant of disease severity.
At later times, recovery is mediated by virus-neutralizing antibodies and cytotoxic T cells.
The viruses are capable of boosting the immune system of the host cell and aids in the formation of interferon.
Mosquitoe act as a vector in transmission of this virus. Chikungunya virus is transmitted between humans via mosquitoes. When an uninfected mosquito feeds upon a viremic person (someone who has the virus circulating in their blood), the mosquito can pick up the virus as it ingests the blood. The virus then undergoes a period of replication in the mosquito, before which time it can then be transmitted back to a new host, when the mosquito next feeds. The virus again begins to replicate in this newly infected person and amplify to high concentrations. If a mosquito feeds on them during the time they have virus circulating in their blood, the mosquito can pick up the virus, and the transmission cycle begins again.
Within the mosquito, the virus replicates in the mosquito midgut. It then disseminates to secondary tissues, including the salivary glands. The virus can be transmitted to a new host more quickly than for other mosquito-borne viruses; laboratory experiments have demonstrated virus can be detected in saliva as little as 2-3 days after the blood meal. This suggests that the complete transmission cycle from human to mosquito, and back to humans can occur in well under a week. Once infectious, the mosquito is believed to be capable of transmitting virus for the rest of its life.
Most commonly, the mosquitoes involved in the transmission cycle are Aedes aegypti and Aedes albopictus. Both species can also transmit other mosquito-borne viruses, including dengue and Zika fever virus.
Symptoms usually starts within 3-7 days after the exposure.
The symptoms of the alpha virus include rash,arthralgia and fever. The Incubation period of the virus include 2-10 days. In the early phase, fever, muscle pains, malaise and headache are present. In the long run this can leads to petechiae,purpura,haemetemesis(vomiting of blood),melaena(blood in stools) and bleeding gums.The joints affected commonly are ankle, wrist and phalanges. The symptoms are similar to other inflammatory joint diseases and it is difficult to differentiate clinically without further investigation.
Detection of virus-neutralizing antibodies in combination with recent travel history to an endemic area may be meaningful.
Immunosorbent assay- detect the virus specific IgM or IgG antibodies.
Greater than fourfold rise in titer between acute and convalescent sera and cerebo spinal fluid containing virus specific IgG or IgM or both are the diagnostic features.
Real time polymerase chain reaction (RT-PCR)- is valuable in the early confirmation of arbovirus infections, particularly chikungunya. However, the value of RT PCR is limited to diagnosis in the viraemic phase, with later infection requiring serology.
Direct immonofluorescense assay -to detect chikungunya IgM has a high sensitivity and specificity and is used in the latter stages.However, the use of these tests in the tropics may be limited by financial constraints.
A normal erythrocyte sedimentation rate- and a negative rheumatoid factor are useful to differentiate chikungunya arthritis from rheumatoid arthritis. Extensive, symmetrical joint involvement, particularly of the metacarpophalangeal and proximal joints, the presence of rheumatoid nodules or anti-cyclic citrullinated peptide (anti-CCP) antibodies favours rheumatoid arthritis over chikungunya with chronic arthropathy. The presence of lower limb asymmetrical joint involvement with axial skeletal affliction favours the diagnosis of spondyloarthropathy over chikungunya.
The prognosis is good under proper medication started at an earlier stages.
