THEORETICAL OVERVIEW OF CHIKUNGUNYA

THEORETICAL OVERVIEW OF CHIKUNGUNYA

CHIKUNGUNYA

            Chkungunya is a relatively rare form of viral fever caused by an alpha virus that is spread by mosquito bites. The name 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. Lumsden (1955) following an outbreak in1955 on them Makonde Plateau, along the border between Mozambique and Tanganyinka (the mainland part of modern day Tanzania). Chikungunya virus infection can cause a debilitating illness, most often characterized by fever, headache, fatigue, nausea, vomiting, muscle pain, rash, and joint pain.

            Acute Chikungunya fever typically lasts a few days to a couple of weeks, but as with dengue              West Nile fever, o'nyong-nyong fever and other arboviral fevers, some patients have prolonged        fatigue    lasting several weeks. Additionally, some patients have reported incapacitating joint pain, or arthritis which may last for weeks or months.  No deaths, neuroinvasive cases, or hemorrhagic cases related to Chikungunya virus(CHIKV) infection have been conclusively documented in the scientific literature. CHIKV infection (whether clinical or silent) is thought to confer life-long immunity. CHIKV is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on a person infected with CHIKV. Monkeys, and possibly other wild animals, may also serve as reservoirs of the virus. Infected mosquitoes can then spread the virus to other humans when they bite.

            Aedes aegypti, a household container breeder and aggressive daytime biter which is attracted to humans, is the primary vector of CHIKV to humans. Aedes albopictus (the Asian tiger mosquito)may also play a role in human transmission is Asia, and various forest-dwelling mosquito species in Africa have been found to be infected with the virus. No vaccine or specific antiviral treatment for Chikungunya fever is available. Treatment is symptomatic--rest, fluids, and ibuprofen, naproxen, acetaminophen, or paracetamol may relieve symptoms of fever and aching. 

Infected persons should be protected from further mosquito exposure (staying                                indoors and/or under a mosquito net during the first few days of illness)   so that they can't contribute to the transmission cycle. The best way to avoid CHIKV infection is to prevent mosquito bites. There is no vaccine or preventive drug for Chikungunya fever.

Epidemiology

             Cikungunya virus is an alpha virus closely related to the O'nyong'nyong virus, the Rose River Virus in Australia and the viruses that cause eastern equine encephalitis and western equine encephalitis. Chikungunya is generally spread through bites from Aedes aegypti mosquitoes,  but recent research by the Pasteur Institute in Paris suggested that Chikungunya virus strains from the 2005-2006 Reunion Island outbreak incurred a mutation that facilitated transmission by Aedes albopictus(Tiger mosquito). Concurrent studies by arbovirologists at the University of Texas Medical Branch in Galveston Texas confirmed definitively that enhanced Chikungunya virus infection of Aedes albopictus was caused by a point mutation in one of the viral envelope genes. Enhanced transmission of chikungunya virus by Aedes albopictus could mean an increased risk for Chikungunya outbreaks in other areas where the Asian tiger mosquito is present.

            In Africa, Chikungunya is spread via a Sylvatic cycle in which the virus largely resides in other primates in between human outbreaks. Since its discovery in Tanganyika Africa in 1952,  Chikungunya virus outbreaks have occurred occasionally in Africa, South Asia, and Southeast Asia, but recent outbreaks have spread the disease over a wider range.The first outbreak in India was in 1963 in kolkatta.

            During 2005-2006, 237 deaths were associated with Chikungunya on Re'union Island   and one third of the island's population were infected. There was also a widespread outbreak in India, primarily in Tamilnadu, Karnataka, Kerala and Andhra Pradesh. After flood and heavy rains in Rajasthan in August 2006, thousands of cases were detected and also in adjoining states like Gujarat and Madhya Pradesh and in the neighbouring country of Sri Lanka.

            From February 2006 to 10 October 2006, the WHO Regional Office for South-East Asia has reported 151 districts in 8 states/provinces of India affected by Chikungunya fever. The affected states are Andhra Pradesh, Andaman & Nicobar Islands, Tamil Nadu, Karnataka, Maharashtra, Gujarat, Madhya Pradesh, Kerala and Delhi. More than 1.25 million suspected cases have been reported from the country, which 752,245 were from Karnataka and 258,998 from Maharashtra provinces. In some areas reported attack rates have reached 45%.

            In the southern Indian state of Kerala, 125 deaths were attributed to Chikungunya with the majority of the casualties reported in the district of Alappuzha primarily in Cherthala.  In October 2006 more than a dozen cases of Chikungunya were reported in Pakistan. In December 2006, an outbreak of 3,500 confirmed cases occurred in Maldieves  and over 60,000 cases in Sri Lanka, with over 80 deaths.

            During June 2007, there was an outbreak in Kerala with 43,138 cases of suspected Chikungunya. In Pathanamthitta, Kottayam,and Alappuzha districts of South Kerala, India claimed more than 50 lives, though no mortality has definitively been linked to chikungunya virus. It is confirmed officially that there are 7000 confirmed Chikungunya patients in these areas. Unofficial reports suggest that more than one hundred thousand are suffering from symptoms of chikungunya. In early 2007, Chikungunya spreaded from Kerala and Tamil Nadu to Sri Lanka and innumerable masses were infected.

Causes

            Chikungunya virus is indigenous to tropical Africa and Asia, where it is transmitted to humans by the bite of infected mosquitoes, usually of the genus Aedes. CHIK fever epidemics are sustained by human-mosquito-human transmission. The word " Chikungunya " is thought to derive from description in local dialect of the contorted posture of patients afflicted with the severe joint pain associated with this disease. The main virus reservoirs are monkeys, but other species can also be affected, including humans.

Treatment

            Chikungunya fever is not a life threatening infection. Symptomatic treatment for mitigating pain and fever using anti-inflammatory drugs along with rest usually suffices. While recovery from Chikungunya is the expected outcome, convalescence can be prolonged (up to a year or more), and persistent joint pain may require analgesic (pain medication) and long-term anti-inflammatory therapy.

Prevention and control

            No vaccine is available against this virus infection. Prevention is entirely dependent upon taking steps to avoid mosquito bites and elimination of mosquito breeding sites. A team from the Ministry of Health and Family Welfare, health officials from Kerala and staff from the WHO India Office and Regional Office for South-East Asia investigated the outbreak in Kerala. They carried out clinical and epidemiological examinations of suspected cases in hospitals and at home, and collected clinical samples. An entomological survey revealed high densities of Aedes albopictus in the affected areas as well as in areas not affected by the disease.

            For personal protection, individuals should take measures to protect themselves against the bites of the mosquitoes which transmit the virus (including Aedes aegypti), which are active during the daytime. Elimination of breeding sites can contribute to the reduction of mosquito densities. As a result, a key recommendation from the investigation team is for urgent vector control measures coupled with an intensive awareness campaign in the community. Health care staff at all levels, government officials and nongovernmental organizations are called upon to assist in this information and health education campaign. The Communication-for-Behavioural Impact methodology has been successful in mobilizing affected populations for vector control activities.

            Use mosquito nets – to protect babies, old people and others, who may rest during the day. The effectiveness of such nets can be improved by treating them with permethrin (pyrethroid insecticide). Curtains (cloth or bamboo) can also be treated with insecticide and hung at windows or doorways, to repel or kill mosquitoes. Mosquitoes become infected when they bite people who are sick with                      Chikungunya. Mosquito nets and mosquito nets and mosquito coils will effectively prevent mosquitoes from biting sick people.

            Control or knockdown of adult infected vector population fogging was carried out to interrupt the transmission. For quicker results, fogging needs to be intensified with 2% Pyrethrum space-spray in the high-risk villages where clustering of cases has been reported from surveillance of fever cases. The Aedes aegypti population was also controlled with the following anti-larval control measures and community based integrated control

Ø        Identification of all water containers having breeding of Aedes larvae and application of Abate (1 ppm) to domestic and peri-domestic non-potable water containers.

Ø        Covering of water containers with tight fitting lid or cloth

Ø        Discarding (and disposing off) tyres and other potential sources of water accumulation.

Ø        Introduction of fishes like guppy and Gambusia in large collections of water in peri-domestic areas.

     Adult mosquitoes can be killed through the following ways

Ø          Making use of commercially available safe aerosols (Pyrethroid-based).

Ø          Spray    bedrooms,      including closets,   bathrooms      and   kitchens (by removing/covering all food items properly) for a few seconds and close the     room for 15-20 minutes. The timing of the spray should coincide with the peak biting times of the Ae. aegypti mosquito, e.g., early morning or late afternoon.

Ø          Use electric bat

To avoid mosquito bites:

Ø        Use mosquito repellents on skin and clothing    When indoors, stay in well-screened areas.

Ø        Use bed nets if sleeping in areas that are not screened or air-conditioned.

Ø        When working outdoors during day times, wear long-sleeved shirts and long pants

Ø        Cover water containers in the house to prevent fresh egg laying.

Ø         Have infants sleep under bed nets during the day.

Ø         Use tight-fitting screens/wire mesh on doors and windows.