Dengue The Deadly Killer
TABLE OF CONTENTS:
Dengue is a mosquito-borne infection which in recent years has become a major international public health concern. Dengue is found in tropical and sub-tropical regions around the world, predominately in urban and peri-urban areas. Dengue haemorrhagic fever (DHF), a potentially lethal complication, was first recognized during the 1950s and is today a leading cause of childhood mortality in several Asian countries. There are four distinct, but closely related, viruses which cause dengue. 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. Indeed, there is good evidence that sequential infection increases the risk of more serious disease resulting in DHF.
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 (see Table 1). South-East Asia and the Western Pacific are most seriously affected. 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 1998 alone, there were more than 616,000 cases of dengue in the Americas, of which 11,000 cases were DHF. 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 Brazil nearly 475,000 cases were reported between January and October 1998 – more than were reported from the entire continent in previous years.
Some other statistics:
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. Infected femalemosquitoes may also transmit the virus to the next generation of mosquitoes by transovarial transmission i.e. via its eggs, but the role of this in sustaining transmission of virus to humans has not yet been delineated. Humans are the main amplifying host of the virus, although studies have shown that in some parts of the world monkeys may become infected and perhaps serve as a source of virus for uninfected mosquitoes. The virus circulates in the blood of infected humans for 2-7 days, at approximately the same time as they have fever; Aedes mosquitoes may acquire the virus when they feed on an individual at this time.
Dengue fever is a severe, flu-like illness that affects infants, young children and adults but rarely causes death. The clinical features of dengue fever vary according to the age of the patient. Infants and young children may have a non-specific febrile illness with rash. Older children and adults may have either a mild febrile syndrome or the classical incapacitating disease with abrupt onset and high fever, severe headache, pain behind the eyes, muscle and joint pains, and rash. Dengue haemorrhagic fever is a potentially deadly complication that is characterized by high fever, haemorrhagic phenomena—often with enlargement of the liver—and in severe cases, circulatory failure. The illness commonly begins with a sudden rise in temperature accompanied by facial flush and other non-specific constitutional symptoms of dengue fever. The fever usually continues for 2-7 days and can be as high as 40-41° C, possibly with febrile convulsions and haemorrhagic phenomena. In moderate DHF cases, all signs and symptoms abate after the fever subsides. In severe cases, the patient's condition may suddenly deteriorate after a few days of fever; the temperature drops, followed by signs of circulatory failure, and the patient may rapidly go into a critical state of shock and die within 12-24 hours, or quickly recover following appropriate volume replacement therapy.
There is no specific treatment for dengue fever. However, careful clinical management by experienced physicians and nurses frequently save the lives of DHF patients. With appropriate intensive supportive therapy, mortality may be reduced to less than 1%. Maintenance of the circulating fluid volume is the central feature of DHF case management.
Vaccine development for dengue and DHF is difficult because any of four different viruses may cause disease, and because protection against only one or two dengue viruses could actually increase the risk of more serious disease. Nonetheless, progress is gradually being made in the development of vaccines that may protect against all four dengue viruses. Such products could be commercially available within several years.
Prevention and Control
At present, the only method of controlling or preventing dengue and DHF is to combat the vector mosquitoes. In Asia and the Americas, Aedes aegypti breeds primarily in man-made containers like earthenware jars, metal drums and concrete cisterns used for domestic water storage, as well as 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 and several Latin American and Caribbean countries as well as two European and one African state. The rapid geographic spread of this species has been largely attributed to the international trade in used tyres. 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 which are encouraged through community-based programmes. The application of appropriate insecticides to larval habitats, particularly those which are considered useful by the householders, e.g. water storage vessels, prevent mosquito breeding for several weeks but must be re-applied periodically. Small, mosquito-eating fish have also been used with some success. 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 sequestered, and the procedure is costly and operationally very demanding. Regular monitoring of the vectors' susceptibility to the most widely used insecticides is necessary to ensure the appropriate choice of chemicals. Active monitoring and surveillance of the natural mosquito population should accompany control efforts in order to determine the impact of the programme
Source: WHO Press Releases, Fact Sheets and Features http://www.who.ch
Dengue fever virus is considered the most important arbovirus in terms of morbidity, mortality and economic cost with an estimated 100 million cases of dengue fever occurring throughout the world annually. Dengue is transmitted by mosquito and occurs in epidemic and endemic proportions throughout tropical and subtropical regions of the world. Infection with dengue virus causes a wide number of clinical symptoms which range in severity. These include fever, a maculopapular rash and headache. Primary infection with dengue usually results in a febrile, self limiting disease, however, secondary infection may result in severe complications such as dengue shock syndrome (DSS) or dengue haemorrhagic fever (DHF). Patients diagnosed with dengue in endemic areas such as South East Asia generally have secondary infection, whereas patients in non endemic areas are usually diagnosed with primary infection. Characteristic antibody responses to the disease enable serological diagnosis and differentiation between primary and secondary dengue.
RNA viruses belong to family Flaviviridae four serotypes (1, 2, 3 and 4) different strains within each serotype
Transmitted by mosquito, principally Aedes aegyptiincubation time ranges from 3 to 10 days
Primary Infection acute febrile illness of sudden onset fever lasting 3 to 5 days headache, myalgia, arthralgia or muscular pain, retro-orbital pain, anorexia fine mculopapular rash on extremities recovery may be associated with fatigue and depression chidren usually have milder disease than adults
Over 90% of cases of DHF and DSS occur in patients previously infected with the virus symptoms are similar to those seen in primary infection, although after a period of 3 to 7 days the patient goes on to display
Bleeding, particularly in skin (petichiae), occaisionally in gunms and nose increased vascular permeability, resulting in leakage of plasma into extravascular spaces and which leads to hypovolaemia haemorrhagic symptoms reduced blood pressure vascular changes and coagulopathy circulatory shock vomiting and abdominal pain lymphadenopathy and hepatomegaly may occur presence of blood in stools, vomitus, urine
Infection will result in lifelong immunity to that serotype, but only temporary immunity to other serotypes
Approximately 5% patients do not produce detectable levels of specific IgM
May not be diagnosed correctly in endemic areas due to generalised and non specific clinical manifestations based mainly on serological methods, as this method is useful in distinguishing primary from secondary infection
Haemagglutination Inhibition Assays (HAI)
Traditional method of diagnosis sera must be acetone or kaolin treated before testing requires paired sera collected at least 7 days apart variance in potency of haemagglutinins made in different laboratories has lead to doubts regarding general applicability
Pre-treatment of sera is not required serial dilution not required - diagnosis can be made from a single serum specimen diagnosis can be from a single serum sample
No Specific treatment for primary dengue Secondary Infection intravenous fluid replacement and use of plasma expanders oxygen therapy blood transfusions in cases of severe bleeding heparin for severe haemorrhage
Presently no vaccine for prevention of disease interruption of breeding cycles of mosquitoes, particularly in stagnant water around the home use of insect repellent and insecticidal treatment and spraying.
Source:PanBio Pty. Ltd., Brisbane, Australia. http://www.panbio.com.au/lit.htm
Almost everyone has had the unpleasant experience of being bitten by a mosquito. Mosquito bites can cause severe skin irritation through an allergic reaction to the mosquito's saliva - this is what causes the red bump and itching. But a more serious consequence of some mosquito bites may be transmission of certain serious diseases such as malaria, dengue fever and several forms of encephalitis. Not only can mosquitoes carry diseases which afflict humans, but they also can transmit several diseases and parasites that dogs and horses are very susceptible to. These include dog heart worms and eastern equine encephalitis.
Aedes Aegypti the Dengue Vector
There are about 200 different species of mosquitoes in the United States, all of which live in specific habitats, exhibit unique behaviors and bite different types of animals. Despite these differences, all mosquitoes share some common traits, such as a four-stage life cycle. After the female mosquito obtains a blood meal (male mosquitoes do not bite), she lays her eggs directly on the surface of stagnant water, in a depression, or on the edge of a container where rainwater may collect and flood the eggs. The eggs hatch and a mosquito larva or "wriggler" emerges. The larva lives in the water, feeds and develops into the third stage of the life cycle called a pupa or "tumbler". The pupa also lives in the water, but no longer feeds. Finally, the mosquito emerges from the pupal case and the water as a fully developed adult, ready to bite.
Mosquito Life Cycle
The type of standing water in which the mosquito chooses to lay her eggs depends upon the species. The presence of beneficial predators such as fish and dragonfly nymphs in permanent ponds, lakes and streams usually keep these bodies of water relatively free of mosquito larvae. However, portions of marshes, swamps, clogged ditches and temporary pools and puddles are all prolific mosquito breeding sites. Other sites in which some species lay their eggs include tree holes and containers such as old tires, buckets, toys, potted plant trays and saucers and plastic covers or tarpaulins. Some of the most annoying and potentially dangerous mosquito species, such as the Asian tiger mosquito, come from these sites.
What You Can Do to Help Fight Mosquitoes
Source: American Mosquito Control Association (AMCA) (a member of the EPA Pesticide Environmental Stewardship Program (PESP)) http://www.epa.gov/pesticides/citizens/mosquito.htm
A citizens body led by president of Bishwa Shahittya Kendra, Prof. Abdullah Abu Sayeed, yesterday launched an awareness campaigne in the capital about dengue infection and its prevention.
According to a press release a group of artists including magician Jewel Aich, TV and stage performer Khairul Alam Sabuj, actress Shirin Bakul and economist Prof. Anisur Rahman and Dr. Atiur Rahman took part in the campaigne.
The group boarding a vehicle distributed leaflets at different points of the city. There were festoons and banners on the the vehicle with various information on the dreaded disease.
Members of the groups sprayed insecticide in some areas and appealed to people to join the campaign to continue for seven days.
They went to different educational institutions including Dhaka college Notre Dame College and Ideal College and encouraged students to begin a civil society movement against Dengue fever.
Source:The Daily Star http://www.dailystarnews.com