CHIKUNGUNYA: A RE-EMERGING PUBLIC HEALTH PROBLEM
Dr. R.Rajendran, Dr.K.Regu and Dr.M.K.Showkath Ali
National Institute of Communicable Diseases
Karaparamba (PO), Kozhikode-673 010 Kerala.
Chikungunya is a relatively rare form of febrile viral disease caused by Alpha virus belongs to the family Togaviridae, transmitted to human beings mainly by Aedes mosquitoes. Chikungunya virus was first isolated during an outbreak of febrile illness during 1952-53 on the Makonde plateau in the Newala province of the East African nation of Tanzania. In fact, the disease derives its name from the language of the tribes in the Makonde plateau of Tanzania, literally meaning “that which bends up”, the term is descriptive of the stooped posture of patients who are afflicted with severe pain and inflammation of the joints-polyarthralgia, which is the typical clinical symptom of the disease.
Chikungunya is geographically distributed in Africa, India and South East Asia. Since 1952 Tanzania outbreak, Chikungunya has caused outbreaks in East Africa (Tanzania and Uganda), in Austral Africa (Zimbabwe and South Africa), in West Africa (Senegal and Nigeria) and in Central Africa (Central African Republic and Democratic Republic of the Congo). The most recent epidemic reemergence was documented in 1999-2000 in Kinshasa, where an estimated 50,000 persons were infected.
Since the first documented Asian outbreak in 1958 in Bangkok, Thailand, outbreaks have been documented in Thailand, Cambodia, Vietnam, Laos, Myanmar, Malaysia, Philippines and Indonesia. The most recent epidemic reemergence was documented in 2001-2003 in Java after 20 years. In both Africa and Asia the reemergence was unpredictable, with intervals of 7-8 years to 20 years between consecutive epidemics.
In India, the first outbreak was recorded in 1963 in Calcutta and was followed by epidemics in Chennai, Pondicherry and Vellore in 1964; Vishakapattinam, Rajmundry, Kakkinada and Nagpur in 1965; Barsi in 1973 and Yawat in 2000.
The ongoing Indian outbreak seems to have followed the Chikungunya outbreak on the Indian Ocean Islands of Comoros, Madagascar, Mayotte, Mauritius, Réunion and Seychelles, which began in the end of 2004.
Since December 2005, massive outbreaks of Chikungunya infection has been ongoing in various states of India - Andhra Pradesh, Karnataka, Maharashtra, Tamil Nadu, Madhya Pradesh, Gujarat, Kerala, Andaman & Nicobar Islands, UT of Lakshadweep, GNCT of Delhi, Rajasthan, Pondicherry and Goa.
The first outbreak of Chikungunya in Kerala was reported from Parasala of Thiruvananthapuram district and Olavanna of Kozhikode district during June 2006. The National Institute of Communicable Diseases, Kerala branch (Kozhikode) has investigated the outbreak in Olavanna and collected 21 sera samples and were tested at National Institute of Communicable Diseases headquarters at Delhi and the National Institute of Virology, Pune. Of this, 17 samples were found positive for Chikungunya. This is the first serologically confirmed case in Kerala.
Investigations indicated that the disease has spread from neighbouring states where the disease was prevalent. The frequent to and fro movement of the population between these states and within, aggravated the situation. From June to November 2006, suspected Chikungunya cases have been reported from all the 14 districts, with highest morbidity in Alappuzha district followed by Thiruvananthapuram, Ernakulam, Palakkad, Pathanamthitta and Kozhikode districts. The affected villages are virtually marooned.
The onset of the disease is typically sudden with malaise and severe debilitating joint pain particularly the knees, hands, wrists, shoulders and low back. The pain was frightening in its severity, completely immobilizing many patients. Within 3-4 hours of onset of joint pain, sudden increase in temperature varying from 102-105º F lasts for 1-6 days. The other symptoms include maculopapular rashes, itching, myalgia, headache, photophobia, nausea and vomiting, occasionally with diarrhoea and ulcer in mouth. Many patients reported that during the initial phase of illness they were unable to keep the feet on ground due to intolerable pain.
The joint pain lasts for weeks to months, severe in elderly people. Even after 5 months, it was observed that difficulties in applying soap on back while bathing, squeezing the cloth while washing, sitting with stretched legs, holding small objects and driving vehicles especially two wheelers, etc are common.
The vectors of Chikungunya are Aedes albopictus and Ae. Aegypti. These mosquitoes are commonly called as ‘tiger mosquitoes’ because of the shining white and black bands of legs and body. The female Aedes mosquito usually becomes infected when it takes blood meal from a person during the acute febrile phase of illness. After an extrinsic incubation period of 3 – 10 days, the virus is transmitted when the infective mosquito bites and injects the salivary fluid into another person. Following an incubation period of 2 –12 days, there is often sudden onset of disease. In case of interrupted feeding, a mosquito can feed on more than one person. This behaviour greatly increases the epidemic transmission efficiency. Thus it is common to see several members of the same household with an onset of illness occurring within 24 hours suggesting that they were infected by the same infective mosquito.
Viraemia is usually present at the time of or just before the onset of symptoms and lasts an average of 5 days after the onset of illness. This is the crucial period when the patient is most infective for the vector mosquito and contributes to maintaining the transmission cycle if the patient is not protected against vector mosquito bites.
The vectors of Chikungunya breed in and around houses and can be controlled by appropriate individual and community action. The eggs of Aedes mosquitoes are laid singly on sides of containers just above the water level. The eggs hatch within 1-2 days. When dried under natural conditions the eggs can retain their viability for up to six months or longer. Flooding and submerging these dried eggs can induce partial hatching from the egg batches. Subsequent drying and flooding can induce further hatching from the remaining unhatched eggs. Generally a female lays about 60-100 eggs per oviposition. Male and female Aedes survives an average of 20 and 30 days respectively. Thus each Aedes female can deposit upto 4-6 batches of eggs with subsequent blood meals.
Aedes mosquitoes are “day biters” bite throughout day with two peaks of biting activities, one at dawn after sunrise and another at dusk before sunset. The flight range of Aedes mosquito is short, will be found around 50-200 metres from the breeding source. Aedes aegypti generally rests indoor in shaded places and Ae. Albopictus prefers to rest outdoor in shrubs and trees. Ae. aegypti mainly bites indoor while Ae. albopictus bites outdoor. Ae. Aegypti lays eggs in practically all types of man-made containers and Ae. albopictus oviposites in both natural and artificial containers.
The Aedes larvae generally breed in clean and unpolluted water. Generally the immature stage of Aedes mosquitoes requires about seven days before adult emergence. As such, any container, natural or artificial, that can accumulate water for that length of time can become a potential breeding habitat for Aedes.
Extensive entomological studies in Kerala show that Ae. albopictus is distributed in both urban and rural areas throughout Kerala and its density is very high and Ae. aegypti is available in very few towns and its prevalence is less than 5%.
Common breeding habitats of Aedes mosquitoes in Kerala:
1. Tyres: Along the National and State Highways tyre repair and resoling shops are common and numerous unwanted tyres are kept in the open, which hold water continuously for several months and acts as a perennial breeding source. Due to automobile explosion, numerous houses are also having unwanted tyres kept in open. 2. Rubber latex collection cups: Rubber plantations are vast and wide spread in Kerala. During rainy season rubber tapping is stopped in thousand of acres of plantations and water collects in each latex collection cups and acts as seasonal breeding source. 3. Cement tanks and cisterns: Ground and overhead tanks and cement cisterns used for storing water. 4. Tar drums and other drums: Numerous full and empty tar drums are the usual sites along the roads and public premises. People use empty drums for storage of water for household purposes. 5. Empty paint tins: After painting of buildings numerous empty paint tins are thrown away in open places. 6. Cocconut shells and husks: Commonly available everywhere and hold water during monsoon season. 7. Grinding stones: Due to common use of mixie and grinders, the conventional grinding stones are kept out side the houses. 8. Mud pots: Due to the advent of beautiful plastic and steel utensils, the mud pots usage has come down and are thrown away from the houses. 9. Flower pots: Empty as well as pots with plants and base trays hold water. 10. Clogged sunshades of buildings and roof gutters. 11. Broken glass bottles and cups. 12. Empty soft drink bottles. 13. Paper cups and other plastic containers. 14. Water trays of refrigerators with automatic defrosting and air conditioner trays. 15. Canoes and small fishing boats, tree holes, bamboo stumps. 16. Leaf axils of banana, colacasia, pineapple, pandaus plants and fallen arecanut leaves. 17. Coco husks and pods. 18. All other containers, which can accumulate water for 5-7 days.
Even the small empty hen’s egg shells can act as a breeding source. The above list is not extensive. In short anything which holds water for more than a week acts as a breeding source for Aedes mosquitoes.
Chikungunya is a man made problem due to lack of knowledge and awareness about the vectors and their breeding sources and transmission. Actually we, the humans rear these mosquitoes in and around our houses, cultivated and uncultivated land with or without our knowledge and get the mosquito bites. Generally mosquitoes bite the persons nearby and if blood source is not available nearby, then only they will go away from the breeding source.
No vaccine is available yet for the prevention of Chikungunya infection and there are no specific drugs for its treatment. Hence Chikungunya control is primarily depend on the control of vector mosquitoes. Aedes larvae are container breeders which breed in both natural and artificial containers. Hence, container management to reduce the sources of breeding habitats is one of the best approaches for controlling Aedes mosquitoes.
This involves any changes that prevents or minimize vector breeding and hence reduces human vector contact. They are source reduction, solid waste management, modification of man made breeding sites and improved house design.
Destruction and elimination of unwanted natural and artificial containers and clearing the unwanted vegetation around houses will definitely contribute to an overall reduction of the Aedes population.
Vector control by the active participation of community with the involvement of local health workers, students, teachers, NGOs such as Neighbourhood groups, residential associations, Kudumbasree, Anganwadi, local body members, social and cultural; organizations will go a long way in Aedes control.
Intensive IEC and health education activities through interpersonal communication, print and electronic media should be imparted to the entire community on war footing and sustained. Vector surveillance and control should also be made as an integral part.
Intersectoral co-ordination is an effective means for successful implementation of vector control. The role of NCC and NSS of various schools and colleges can play a vital role to control mosquito breeding thereby elimination of mosquito-borne diseases. The recent initiatives of the NSS of schools and colleges in Health education and vector control is worth mentioning.
If each and every one of us keep our houses and premises, free from mosquito breeding, then the mosquito-borne diseases such as Malaria, Filariasis, Dengue/Dengue Haemorrhagic Fever, Chikungunya, Japanese Encephalitis, etc can be controlled easily, otherwise the problems and their complications will increase year by year.
