diease

Chikungunya


OVERVIEW OF Chikungunya :

Chikungunya is caused by the alpha virus.  The mosquitoe taking part in the infection of the disease is through Aedes aegypti, Aedes albopictus


STRUCTURE of Chikungunya :

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


CAUSES :

They are zoonotic pathogens and reside in the mosquitoe act as the main vector for the disease. The alpha virus causes the following

 

Alphaviruses Producing Fever, Polyarthritis, and Rash:
 

Chikungunya Virus

Chikungunya Virus belongs to the genus alphaviruses. Chikungunya virus is most commonly seen in among Asian and African Populations. There are 3 possible modes of transmission, the first mode is sporadic cases arising when man come in contact with the jungle areas where the reservoir is in monkeys. Chikungunya is also prevalent in Thailand, where people to people spread occur by mosquitoes. The third type of Chikungunya exists in India, when during the rainy season, the population of mosquitoes increases greatly and epidemics can occur.

The clinical disease is a flu-like fever of acute onset, followed by a pharyngitis, maculopapular rash and arthritis. Minor haemorrhagic manifestations are occasionally seen. The diagnosis of infection is usually made by serology.

There are several other alphaviruses which produces a similar picture to that of Chikungunya virus;-

  1. O'nyong-nyong virus - found mainly in East Africa.
  2. Sindbis virus - clinical cases of sindbis disease have been reported from Africa, Middle East, Asia and Africa. Sindbis virus is maintained in nature by a cycle involving mosquito-bird- mosquito.
  3. Mayaro virus - found in S. America
  4. Ross River virus - causes epidemics in Australia and S.Pacific islands.
  5. Ockelbo virus - Sweden and USSR.


PATHOPHYSIOLOGY :

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.


ROUTES OF TRANSMISSION :

             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.

 

 


COMMON CLINICAL SIGNS AND SYMPTOMS :

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.


DIAGNOSTIC :

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.


TREATMENT AND PROGNOSIS :

Corticosteroids are not recommended since it might result in immunosuppression.

Passive immunotherapy by the administration of anti CHIKV hyperimmune human intravenous antibodies(immunoglobulins) might provide a great relief to chikungunya patients.

Medications used:

Acetaminophen

Naproxen

Ibuprofen

 


PROGNOSIS :

The prognosis is good under proper medication started at an earlier stages.


PREVENTION :

  • Wear light coloured clothing and cover your body as much as possible
  • Get plenty of water and stay away from dehydration
  • Use mosquito repellents containing DEET (N,N dimethyl meta toluamide) on exposed skin
  • Use mosquito coils and electric vaporization mats both day and night
  • Use mosquito nets
  • Use door and window screens (mesh)
  • Use full sleeve to protect yourself from mosquitoes.


Medicines used in the Treatment :

Acetaminophen

Naproxen

Ibuprofen