The chikungunya virus: Bangladesh perspective

MORE than 120 mosquito species have been recorded in Bangladesh during 1908–2016. More than 25 of them are Aedes species, which are responsible for carrying and transmitting the chikungunya virus, as well as many other diseases, to humans. Aedes aegypti and Aedes albopictus are proven culprits for chikungunya.
The first case of chikungunya was described during an outbreak of febrile illness during 1952 in the Newala Province of Southern Tanzania. The name ‘chikungunya’, given by local villagers, means ‘bending up or contorting’, reflecting disease symptoms of severe joint pain and limited movement.
However, there are scientific theories that hypothesise that the chikungunya virus outbreak may have happened long before 1952 in different parts of Africa, Asia and the Pacific. They may have been misidentified as dengue fever because of their similar clinical symptoms. This disease moved mostly through the trading routes that time. If we ignore these potential outbreaks, we see that the chikungunya activity remained low for another 48 years around Africa, Asia and the Indian subcontinent.
In 1999–2000, there was a large outbreak of chikungunya in the Democratic Republic of the Congo, followed by several more outbreaks in islands of the Indian Ocean and Gabon. A large number of imported cases in Europe were associated with this outbreak, mostly in 2006 when the Indian Ocean outbreak was at its peak. Since 2005, India, Indonesia, the Maldives, Myanmar and Thailand have reported over 1.9 million cases of chikungunya and ultimately spilled over to south-western part of Bangladesh in 2008. In 2007, the first local transmission was reported in Europe, taking place in north-eastern Italy. There were 197 cases recorded during this outbreak and it was confirmed to be mosquito-borne outbreaks by Aedes albopictus.

Current epidemiology
TO DATE, the chikungunya virus has been identified in more than 60 countries in Asia, Africa, Europe and the Americas. Uptil 2013, chikungunya was mostly confined to Africa, Asia and the Indian subcontinent but in December 2013, France reported two laboratory-confirmed cases in the French region of a Caribbean island in St Martin. Since then, local transmission has been confirmed in more than 43 countries and territories in the WHO Region of the Americas. This is the first documented outbreak of chikungunya with autochthonous transmission in the Americas. As of April 2015, more than 1. 4 million suspected cases of Chikungunya have been recorded in the Caribbean islands, Latin American countries, and the United States of America. One hundred and ninety-one deaths have also been attributed to this disease in the period. Canada, Mexico and the United States have also recorded imported cases.

Signs and symptoms
A bite by either Aedes aegypti or Aedes albopictus, a mosquito carrying the chikungunya virus, may lead to an abrupt onset of fever, malaise (ill feeling), and frequently accompanied by joint pain usually after a week ranging from two to 12 days. The joint pain is often very debilitating, but usually lasts for a few days or may prolong to weeks. Other common signs and symptoms include muscle pain, headache, nausea, fatigue, photophobia and a macular (red small flat) or maculopapular (red small flat with small blister) rash. Dengue, yellow fever and the Zia virus may show similar symptom if present in that area. 
Many can get this virus through a mosquito bite but may never develop any symptoms. However, some may experience severe joint pain that persist for weeks to several months, or even years. Occasional cases of eye, neurological and heart complications have been reported, as well as gastrointestinal complaints. Serious complications are not common, but in young children or older adults, the disease can contribute to the cause of death. Often symptoms in infected individuals are mild and the infection may go unrecognised, or misdiagnosed in areas where dengue occurs.

Virus transmission
IN URBAN settings, chikungynya virus transmitted from human to human through the bites of infected female mosquitoes. The risk of a person transmitting the virus to a biting mosquito or through blood is highest when the patient is viremic (viruses in blood), usually during the first 2–6 days of illness. Most commonly, the mosquitoes involved are Aedes species and Aedes aegypti which can transmit other mosquito-borne viruses, including dengue which is common in many parts of Dhaka city and outside. These mosquitoes can be found biting throughout daylight hours although there may be peaks of activity in the early morning and late afternoon. They are not very active at night compared with day-time but risk should not be ignored. Both species are found biting outdoors, but Aedes aegypti will also readily feed indoors. After the bite of an infected mosquito, the onset of illness occurs usually between four and eight days but can range from two to 12 days. 
Maternal-foetal transmission has been documented during pregnancy; the highest risk occurs when a woman is viremic at the time of delivery, however, chikungunya virus is transmitted rarely from mother to newborn around the time of birth. Transmission of chikungunya virus through breastfeeding has not been reported yet; so, mothers are encouraged to breastfeed even in areas where chikungunya virus is circulating. In theory, the virus could spread through a blood transfusion or organ transplants, but no cases has yet been documented. There is also no evidence to show that chikungunya undergoes the sylvatic cycle — meaning the virus cycles between other non-human primate, small animals, and mosquitoes in-between human outbreaks.

Diagnosis and care
A PRELIMINARY diagnosis can be made by physicians based on careful evaluation of a patient’s signs and symptoms and travel history, as well as the status of local chikungunya activity in humans and primates in the area. For definitive diagnosis, several methods can be used. Serological tests, such as enzyme-linked immune-sorbent assays, may confirm the presence of Immunoglobulin M and Immunoglobulin G anti-chikungunya antibodies. Immunoglobulin M antibody levels are the highest three to five weeks after the onset of illness and persist for about two months. Samples collected during the first week after the onset of symptoms should be tested by both serological and molecular methods.
Differentiating between dengue and chikungunya is difficult since both viruses are being transmitted by the same mosquito and show some common symptoms. Where the above laboratory tests are not feasible, rapid heart rate, cough, and fever at presentation and duration and others were predictive of chikungunya. Bleeding, the presence of fever and longer duration of illness at presentation were indicative of dengue haemorrhagic fever while a longer duration of fever and a higher platelet count increased the odds that the patient had chikungunya.
FOR those who sleep during the daytime, particularly young children, seniors, or those with other illnesses, insecticide-treated mosquito nets can offer a good protection. Mosquito coils or other insecticide vaporisers may also reduce indoor biting. Basic precautions should be taken by people travelling to risk areas and these include use of repellents, wearing long sleeves and pants and ensuring rooms are fitted with screens to prevent mosquitoes from entering.

Treatment and prevention
THERE is no specific antiviral drug treatment for chikungunya but for supportive care. Treatment is directed primarily at relieving the symptoms, including the joint pain using anti-pyretics, optimal analgesics and fluids. In Africa, small groups of patients suffering chronic arthritic pains of more than five years after a chikungunya infection were treated in an open study with chloroquine, and achieved some improvement in their symptom. No definitive clinical trials have been completed. There is also no commercial chikungunya vaccine to date.
Reduce open water around houses: The proximity of mosquito breeding sites to human habitation is a significant risk factor for chikungunya as well as for other diseases that these species transmit. Prevention and control relies heavily on reducing the number of natural and artificial water-filled container habitats that support breeding of the mosquitoes. 
People often wonder if small amounts of outdoor water can breed mosquitoes. The answer is yes. Even one tea spoon of water can support breeding of thousand mosquitoes. Thus careful inspection in and around your residence is necessary. This requires mobilisation of communities, check the homes of your neighbours and friends. 
Use of insecticides during outbreaks: During outbreaks, insecticides may be sprayed to kill flying mosquitoes, applied to surfaces in and around containers where the mosquitoes land, and used to treat water in containers to kill the immature larvae. 
For protection during outbreaks of chikungunya, clothing which minimises skin exposure to mosquitoes is advised such as long shirts and long pants. Repellents can be applied to exposed skin or to clothing in strict accordance with product label instructions.
Biological control: Biological control could effectively disrupt mosquito breeding cycles and thus reduce mosquito borne diseases since no effective vaccine or medicine is available for these mosquito borne diseases. The following biological control independently or in combination can be sued. Those are bacterial or fungal toxins, plant-based mosquitocides, and introducing aquatic fauna in city drains. 
Uses of genetically modified mosquitoes to kill wild mosquitoes: Researchers created different kind of mosquitoes, which will ultimately reduce mosquito population. Among them sterile mosquito, genetically modified mosquitoes and endosymbiotic bacteria containing mosquitoes are notable.
None of the single methods mentioned above will be able to eradicate them fully. Thus application of combined methods should be implemented for a long term basis after proper scientific consultations.

Aedes aegypti and Aedes albopictus
BOTH Aedes aegypti and Aedes albopictus have been implicated in large outbreaks of chikungunya. While Aedes aegypti is confined within the tropics and sub-tropics, Aedes albopictus also occurs in temperate and even cold temperate regions. In recent decades Aedes albopictus has spread from Asia to become established in areas of Africa, Europe and the Americas. The species thrives in a wider range of water-filled breeding sites, including coconut husks, cocoa pods, bamboo stumps, tree holes and rock pools, in addition to artificial containers such as vehicle tyres and saucers beneath plant pots. This diversity of habitats explains the abundance of Aedes albopictus in rural as well as peri-urban areas and shady city parks.
Aedes aegypti is more closely associated with human habitation and uses indoor breeding sites, including flower vases, water storage vessels and concrete water tanks in bathrooms, as well as the same artificial outdoor habitats as Aedes albopictus. In Africa, several other mosquito vectors have been implicated in disease transmission. There is evidence that some animals, including non-primates, rodents, birds and small mammals, may act as reservoirs.

Future directions
Because of climate change and increased global travel, the introduction of new viruses is inevitable. The upsurge of mosquito borne illnesses open opportunities for the government, medical community, universities, research institutions, social workers, and media working together. Surveillance (human, mosquitoes and animal), clinical management and public education are keys to combat this crisis.

Dr Muhammad Morshed is a clinical professor of pathology and laboratory medicine at the University of British Columbia and programme head, zoonotic and emerging pathogens, BC Centre for Disease Control, Public Health Microbiology Laboratory, Vancouver, Canada.

News Courtesy: www.newagebd.net