COMMUNICABLE DISEASES DENGUE FEVERDr Abu Zar TaizaiPublic Health SpecialistMMBS, MPH (Distinction)Ex-Consultant WHO
DENGUE A MAJOR GLOBAL HEALTH PROBLEM Dengue in recent years has become a major international public health concern. Dengue is found in tropical and sub-tropical regions around the world, predominantly in urban and semi-urban areas. Dengue Haemorrhagic fever (DHF) a potentially lethal complication was first recognized in the 1950s during the dengue epidemics in the Philippines and Thailand, but today DHF affects most Asian countries and has become a leading cause of hospitalization and death among children.
The global prevalence of dengue has grown dramatically in recent decades. The disease is now endemic in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, South- east Asia and the Western Pacific. South-east Asia and the Western Pacific are most seriously affected. Before 1970 only nine countries had experienced DHF epidemics, a number that had increased more than four-fold by 1995. Some 2500 million people - two fifths of the worlds population - are now at risk from dengue. WHO currently estimates there may be 50 million cases of dengue infection worldwide every year.
In 2001 alone, there were more than 609000 reported cases of dengue in the Americas, of which 15000 cases were Dengue Haemorrhagic Fever. This is greater than double the number of dengue cases which were recorded in the same region in 1995. Not only is the number of cases increasing as the disease is spreading to new areas, but explosive outbreaks are occurring. In 2001, Brazil reported over 390000 cases including more than 670 cases of DHF.
An estimated 500,000 cases of DHF require hospitalization each year, of whom a very large proportion are children. At least 2.5% of cases die, although case fatality could be twice as high. Without proper treatment, DHF case fatality rates can exceed 20%. With modern intensive supportive therapy, such rates can be reduced to less than 1%. The spread of dengue is attributed to expanding geographic distribution of the four dengue viruses and of their mosquito vectors, the most important of which is the predominantly urban species Aedes aegypti. A rapid rise in urban populations is bringing greater numbers of people into contact with this vector, especially in areas that are favourable for mosquito breeding, e.g. where household water storage is common and where solid waste disposal services are inadequate
In Asia and Amrecas the Aedes aegypti breeds primarily in man-made containers like: Earthenware jars, Metal drums and Concrete cisterns used for domestic water storage. Discarded plastic food containers Used automobile tyres and other items that collect rainwater. In Africa it also breeds extensively in natural habitats such as tree holes and leaf axils.
In recent years, Aedes albopictus, a secondary dengue vector in Asia, has become established in the United States, several Latin American and Caribbean countries, in parts of Europe. The rapid geographic spread of this species has been largely attributed to the international trade in used tyres.
Dengue Syndrome Dengue fever and dengue hemorrhagic fever (DHF) are viral diseases transmitted by Aedes mosquitoes, usually Aedes aegypti. There are four types of this virus (serotypes 1 to 4) and are closely related to one another. Recovery from infection by one provides lifelong immunity against that serotype but confers only partial and transient protection against subsequent infection by the other three. There is good evidence that sequential infection increases the risk of more serious disease resulting in DHF.
Dengue viruses are capable of infecting humans and causing disease. These infections may be symptomatic, or may lead to:3. “Classical” dengue fever5. Dengue Haemorrhagic fever without shock7. Dengue Haemorrhagic fever with shock
CLASSICAL DENGUE FEVER Reservoir both man and mosquito The mosquito becomes infective by feeding on the patient from the day before onset to the 5th day of illness. After an extrinsic incubation period of 8-10 days the mosquito becomes infective and is able to transmit infection. The illness is characterized by an incubation period of 3-10 days.11. Onset is sudden with chills and high fever. Temperature rises quickly as high as 104° F (40° C), with relative bradycardia and hypotension.
1. Reddened eyes3. Intense muscles and joint pains5. A flushing or pale pink rash comes over the face and then disappears. The glands (lymph nodes) in the neck and groin are often swollen7. Fever lasts 2-4 days rarely more than 7 days.9. Recovery is complete11. Case fatality is very low
Dengue Haemorrhagic Fever Dengue hemorrhagic fever is a more severe form of the viral illness. Caused by more than one dengue viruses. It is due to double infection with dengue virus. The first infection sensitizes the patient and the second appears to produce immunological catastrophe.Manifestations include: Headache, high fever (continuous and lasting 2-7 days) Rash, and evidence of hemorrhage in the body (Petechiae) Bleeding in the nose or gums, Black stools, or easy bruising are all possible signs of hemorrhage. This form of dengue fever can be life-threatening or even fatal.
THERE IS NO DRUG FOR DENGUE. To prevent dengue fever, you must prevent the breeding of its carrier, the Aedes mosquitoes.TreatmentBecause dengue is caused by a virus, there is no specificmedicine or antibiotic to treat it.For typical dengue, the treatment is purely concernedwith relief of the symptoms (symptomatic).Rest and fluid intake for adequate hydration isimportant.
Immunization Vaccine development for dengue and DHF is difficult because any of four different viruses may cause disease. Nonetheless, progress is being made in the development of vaccines that may protect against all four dengue viruses. Such products may become available for public health use within several years.
The mosquito flourishes during rainy seasons but can breed in water-filled flower pots, plastic bags, and cans year-round. One mosquito bite can inflict the disease. Under optimal conditions, the egg of an Aedes mosquito can hatch into a larva in less than a day. The larva then takes about four days to develop in a pupa, from which an adult mosquito will emerge after two days. Three days after the mosquito has bitten a person and taken in blood, it will lay eggs, and the cycle begins again.
Facts about the mosquito Only the female aedes mosquito bites as it needs the protein in blood to develop its eggs. The mosquito becomes infective approximately 7 days after it has bitten a person carrying the virus. This is the extrinsic incubation period, during which time the virus replicates in the mosquito and reaches the salivary glands.
Peak biting is at dawn and dusk. The average lifespan of an Aedes mosquito in Nature is 2 weeks. The mosquito can lay eggs about 3 times in its lifetime, and about 100 eggs are produced each time. The eggs can lie dormant in dry conditions for up to about 9 months, after which they can hatch if exposed to favourable conditions, i.e. water and food.
Prevention The application of appropriate insecticides to larval habitats. During outbreaks, emergency control measures may also include the application of insecticides as: space sprays to kill adult mosquitoes using portable or truck-mounted machines or even aircraft. However, the killing effect is only transient, variable in its effectiveness because the aerosol droplets may not penetrate indoors to microhabitats where adult mosquitoes are hiding.
Dengue Prevention Checklist To prevent the spread of dengue fever, we must first prevent the breeding of its vector, the Aedes mosquitoes. The Aedes mosquito is easily identifiable by its distinctive black and white stripes on their body. It prefers to breed in clean, stagnant water easily found in our homes. We can get rid of the Aedes mosquito by frequently checking and removing stagnant water in our premises.
CHECKLISTAt all times Turnpails and watering cans over and store them under shelter.
Remove water in plant pot plates. Clean and scrub the plate thoroughly to remove mosquito eggs. Avoid the use of plant pot plates, if possible.
Loosen soil from potted plants to prevent the accumulation of stagnant water on the surface of the hardened soil. Do not block the flow of water in scupper drains.
Cover rarely used gully traps. Replace the gully trap with non-perforated ones and install anti-mosquito valves.
No tray or receptacles should be placed beneath and or/ on top of any air-conditioning unit so as not to create a condition favourable for mosquito breeding.Every other day Change water in flower vases. Clean and scrub the inner sides of vases. Wash roots of flowers and plants thoroughly as mosquito eggs can stick to them easily.
Once a week Clear fallen leaves and stagnant water in your scupper drains and garden. These leaves could collect water or cause blockages to the drains, thus resulting in the build-up of stagnant water. Clear any stagnant water in your air cooler unit.Once a month Add prescribed amounts of sand granular insecticide into vases, gully traps and roof gutters, even if they are dry.