A global pandemic of dengue began in Southeast Asia after World War II and has intensified during the last 15 years. Epidemics caused by multiple serotypes are more frequent, the geographic distribution of dengue viruses and their mosquito vectors has expanded and Dengue Hemorrhagic Fever (DHF) has emerged in the Pacific region and the Americas. The disease is now endemic in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific.

Before 1970 only nine countries had experienced DHF epidemics, a number which had increased more than four-fold by 1995. Some 2500 million people -- two fifths of the world's population -- are now at risk from dengue. WHO currently estimates there may be 50 million cases of dengue infection worldwide every year. In Southeast Asia, epidemic DHF first appeared in the 1950s, but by 1975 it had become a leading cause of hospitalisation and death among children in many countries in that region (CDC 2000).

Situation in Bangladesh: First outbreak of dengue fever (Dhaka fever) was documented in 1964 in Dhaka followed by few scattered cases of DF during 1977-78. In 1996-97 dengue infections were confirmed in 13.7 per cent of 255 fever patients screened at Chittagong Medical College. The first epidemic of dengue hemorrhagic fever occurred in mid 2000, when 5551 dengue infections were reported from Dhaka, Chittagong and Khulna cities, occurring mainly among adults. Among the reported cases 4385 (62.4%) were dengue fever infections and 1186 (37.6%) dengue haemorrhagic fever. The case fatality rate was 1.7% with 93 deaths reported. Aedes aegypti was identified as the main vector responsible for the epidemic and Aedes albopictus was identified as a potential vector in Chittagong.

The worst outbreak was in 2002 with 6,104 cases and 300 deaths. In 2004, a total of 3,934 cases with 13 deaths (CFR = 0.33%) were reported. The epidemic started in June, peaked in July (1,209) and continued through August. During the outbreak period, 98 per cent of the cases were from Dhaka with a case fatality rate of 2.3 per cent. The rest of the cases were from districts of Khulna, Jessore, Barishal, Comilla, Chittagong, Jhinaidah, Sirajgonj, and Madaripur. In 2005 there were 1048 reported cases and 4 deaths (CFR 0.38%). In 2006 the number of cases and deaths increased two fold as compared to 2005. The maximum transmission period is July to September each year since 2000. This year 37 suspected dengue cases had already been admitted in different hospitals in Dhaka till July. A recent DCC survey found that 8 out of its 10 zones have an alarming concentration of Aedes mosquito.

Seasonal trend: Dengue occurs mostly in rainy season and the present trend in Bangladesh shows its occurrences between May to December with peak incidence between June and October.

Risk factors: It has been seen that in tropical country, rainy season, scattered collection of water in artificial containers (eg bottles, tires, tire casing, flower vases, discarded boxes, cans, empty oil-barrels), uncovered water-storage, cultivation necessitated temporary water accumulation, vector density, plants with temporary water pool, empty receptacles in gardens and courtyards and animal water container are all potential risk factors for dengue (John M Hayes et al, 2003).

Clinical features and complications: Dengue fever usually starts suddenly with a high fever, rash, severe headache, pain behind the eyes, and muscle and joint pain. The severity of the joint pain has given dengue the name "break-bone fever." Nausea, vomiting, and loss of appetite are common. A rash usually appears 3 to 4 days after the start of the fever. The illness can last up to 10 days. Most dengue infections result in relatively mild illness, but some can progress to dengue hemorrhagic fever. With DHF, the blood vessels start to leak and cause bleeding from the nose, mouth, and gums. Bruising can be a sign of bleeding inside the body. Without prompt treatment, the blood vessels can collapse, causing shock (DSS). DHF is fatal in about 5 percent of cases, mostly among children and young adults.

Transmission: Dengue viruses are transmitted to humans through the bites of infective female Aedes mosquitoes. Mosquitoes generally acquire the virus while feeding on the blood of an infected person. Once infective a mosquito is capable of transmitting the virus to susceptible individuals for the rest of its life, during probing and blood feeding.

Policy, strategy and objectives: There is no specific treatment for dengue fever. Moreover, vaccine development is difficult since any of four different dengue serotypes may cause the disease, and protection against only one or two of these serotypes might actually increase the risk of more serious disease. Nevertheless, progress is being made in the development of vaccines that may protect against all four serotypes.

Present elements of strategy should include surveillance of vector density and disease transmission, developing selective and sustainable vector control measures with preparedness for emergency control, strengthening local capacity for assessment of social, cultural, economic and environmental factors that lead to increased vector densities and transmission of disease, early diagnosis and prompt treatment for DHF and DSS, research in vector control and mobilisation of other sectors to incorporate dengue control in their goal and activities.

Prevention and control: At present, the only method of controlling or preventing dengue and DHF is to combat the vector mosquitoes. Vector control is implemented using environmental management and chemical methods. Proper solid waste disposal and improved water storage practices, including covering containers to prevent access by egg laying female mosquitoes are among methods that are encouraged through community-based programmes. The application of appropriate insecticides to larval habitats, particularly those which are considered susceptible use of bed nets, screening sleeping areas, eliminating mosquito breeding sites around homes, discarding items that can collect rain or run-off water, regularly changing the water in outdoor bird baths and pet and animal water containers are of paramount importance to prevent dengue.

Conclusion: Dengue and dengue hemorrhagic fever have emerged as a major public health problem in Bangladesh. Dengue is easily preventable, with self-awareness and collective campaigning to seek public cooperation in keeping neighbourhoods clean. City corporations by taking appropriate vector control measure coupled with arrangements for drainage of logged water can save many from intense suffering and averting deaths from DHF and DSS in the future days to come.

Dr Zulfiquer Ahmed Amin is a physician, specialist in Public Health and Health Economics.