Chikungunya overview

# Overview
Chikungunya virus (CHIKV) is an arthropod-borne virus, of the genus Alphavirus, that is transmitted to humans by virus-carrying Aedes mosquitoes.
CHIKV is transmitted similarly to dengue fever and causes an illness with an acute febrile phase lasting two to five days, followed by a longer period of joint pains in the extremities; this pain may persist for years in some cases.
The best means of prevention is overall mosquito control and in addition, the avoidance of bites by any infected mosquitoes. There is no specific treatment currently available but medications can be used to reduce symptoms.

# Historical Perspective
The name chikungunya is derived from the Makonde word meaning "that which bends up" in reference to the stooped posture developed as a result of the arthritic symptoms of the disease. The disease was first described by Marion Robinson and W.H.R. Lumsden in 1955, following an outbreak on the Makonde Plateau, along the border between Tanganyika and Mozambique, in 1952.  Chikungunya is closely related to O'nyong'nyong virus.

# Pathophysiology
Chikungunya virus (CHIKV) belongs to the alphavirus genus of the Togaviridae family and is transmitted by mosquito bites. Both innate and adaptive immunity are involved in the pathogenesis of CHIKV infection.

# Causes
Chikungunya virus is an alphavirus with a positive sense single-stranded RNA genome of approximately 11.6kb. It is a member of the Semliki Forest Virus complex and is closely related to Ross River Virus, ONyong Nyong virus and Semliki Forest Virus. In the United States it is classified as a Category C priority pathogen and work requires Biosafety Level 3 precautions.
Human epithelial, endothelial, primary fibroblasts and monocyte-derived macrophages are permissive for chikungunya virus in vitro and viral replication is highly cytopathic but susceptible to type I and II interferon. In vivo, chikungunya virus appears to replicate in fibroblasts, skeletal muscle progenitor cells and myofibers.

# Differential Diagnosis
Chikunguyna must be differentiated from other diseases that present with flu like symptoms such as fever, headache, fatigue, joint aches or arthralgias, myalgias. Diseases with similar symptoms include dengue, influenza, measles, rubella, malaria, and yellow fever.

# Epidemiology and Demographics
Chikungunya was first described in Tanzania, Africa in 1952. Chikungunya outbreaks have occurred in countries in Africa, Asia, Europe, and the Indian and Pacific Oceans. In late 2013, the first local transmission of chikungunya virus in the Americas was identified in Caribbean countries and territories. Local transmission means that mosquitoes in the area have been infected with the virus and are spreading it to people.

# Risk Factors
People who travel to the Caribbean, Africa, Asia, islands in the Indian Ocean and Western Pacific are at risk as the virus is present in many of these areas. People at risk for more severe disease include newborns infected around the time of birth, older adults (65 years), and people with medical conditions such as high blood pressure, diabetes, or heart disease.

# Natural History, Complications and Prognosis
Complications are rare and include uveitis, retinitis, myocarditis, hepatitis, nephritis, bullous skin lesions, hemorrhage, meningoencephalitis, myelitis, Guillain-Barre syndrome, and cranial nerve palsies.  Persons at risk for severe disease include neonates exposed intrapartum, older adults (e.g., > 65 years), and persons with underlying medical conditions (e.g., hypertension, diabetes, or cardiovascular disease). Most patients recover uneventfully, but variable proportions of patients may have persistent arthralgias (joint pains) for months to years.

# Diagnosis

## History and Symptoms
Chikungunya which follows a bite of an infected mosquito Aedes aegypti or Aedes albopictus carrying chikungunya virus, can either present as an asymptomatic or as a symptomatic disease.  The most common symptoms of the symptomatic disease include fever, arthralgia or polyarthritis, and maculopapular rash.

## Physical Examination
Chikungunya usually presents with clinical signs such as fever, skin rashes, and joint swelling with effusions that can be detected during a physical examination.

## Laboratory Findings
There are no pathognomonic laboratory findings for Chikungunya virus infection. Laboratory abnormalities include mild thrombocytopenia (>100,000/mm3), neutropenia, lymphopenia, and elevated liver function tests. Erythrocyte sedimentation rate and C-reactive protein are usually elevated.

# Treatment

## Medical Therapy
There is no specific antiviral therapy for chikungunya virus. The treatment of the disease is based on decreasing the symptoms and maintain proper hydration. Paracetamol is the drug of choice and treatment should be instituted in all suspect cases without waiting for serological or viral confirmation.  All suspected cases should be kept under mosquito nets during the febrile period.

## Prevention
In the absence of an effective vaccine to prevent chikungunya virus infection, the only available tool to prevent the infection is by reducing the human-vector contact.