DENGUE - THE CURRENT PROBLEM

           Dengue is a tropical disease which is caused by dengue virus. Dengue is transmitted by mosquitoes especially with genus Aedes i.e. Aedes aegypti. In very rare cases the disease is life threatening while many a times the symptoms are asymptomatic or only have mild symptoms. As such there is no commercially vaccine.

ABOUT VIRUS :- Dengue fever virus is a RNA type virus belongs to family of Flaviviridae and genus Flavivirus. Transmission of virus is through arthropods i.e. via arbovirus ( arthropod borne virus ). Genome of virus contain about 11,000 nucleotide base which is coding for different types of proteins that are C, prM and E, together comprise the viral particle. Four strains of the virus present in atmosphere are DENV-1/ D-1, DENV-2/ D-2, DENV-3/D-3, DENV-4/ D-4.

TRANSMISSION:- Primarily the virus is transmitted through Aedes aegypti. While other species involved in transmitting the disease are A.scutellaris, A.albopictus, A.polynesiensis. Mosquito bite is generally during day time, particularly in early morning or evening. Humans are primary host. Yet many a times primates are also infected. Usually single bit is enough to contract the disease. Virus transmission is also possible through vertical transmission ( from mother to child ) and during organ transplant.

             Female mosquito takes a blood from a person who infected with dengue fever and then becomes itself infected with the virus. About 8–10 days later, the virus spreads to other tissues including the salivary glands of mosquito and is subsequently present its saliva. With contact with human/primates the virus is released inside the host. The virus seems to have no harmful effect on the mosquito, which remains infected for life. 

             
         Once virus enters the host, it binds to cell lining and enters white blood cells, It reproduces inside the cells while they move throughout the body. The white blood cells respond to virus by producing a number of signaling proteins, such as interferon, which are responsible for many of the general symptoms, such a fever, flu-like symptoms and the severe pains. In severe infection occurs , the virus multiplication inside the body is greatly increased, and many more organs can be affected. Furthermore, dysfunction of the bone marrow leads to reduced numbers of platelets, which are necessary for effective blood clotting; this increases the risk of bleeding, the other major complication of dengue fever.

              Once inside the skin, dengue virus binds to Langerhans cells. (a population of dendritic cells.). The dendritic cell moves to the nearest lymph node. Meanwhile, the virus genome is translated in membrane-bound vesicles on the cell's endoplasmic reticulum. Here cell's protein synthesis apparatus produces new viral proteins that replicate the viral RNA and begin to form viral particles. Immature virus particles are transported to the Golgi apparatus and complete mature particle is formed. Mature new viruses bud on the surface of the infected cell and are released through exocytosis. 

              The incubation period (time between exposure and onset of symptoms) ranges from 3–14 days. And therefore, travelers returns from endemic areas show likely symptoms are unlikely to have dengue. Children often experience symptoms similar to those of the common cold and gastroentritis and, though initial symptoms are generally mild but include high fever. Symptoms ignored in children’s or old people can give rise to severe dengue infection which can be life threatening and thus preliminary precautions has to be taken.

SIGNS AND SYMPTOMS:-

                       The general characteristic symptoms of dengue are sudden-onset fever, headache  muscle and joint pains, and a rash. The alternative name for dengue, "break-bone fever", comes from the associated muscle and joint pains. The course of infection is divided into three phases: febrile, critical, and recovery. Phases are associated with pain headache for  3 to 6 days while may a times vomiting is seen due to abdominal discomfort. Measles like rashes are prominently visible, this symptoms should be confused with measles. The fever itself is classically biphasic in nature, breaking and then returning for one or two days, although there is wide variation in how often this pattern actually happens.

                    In some people, the disease proceeds to a critical phase. During this phase there may be significant fluid accumulation in the chest and abdominal cavity due to increased capillary permeability and leakage. This leads to depletion of fluid from the circulation and decreased blood supply to vital organs. During this phase, organ dysfunction and severe bleeding, typically from the gastrointestinal tract, may occur. Shock (dengue shock syndrome) and hemorrhage (dengue hemorrhagic fever) occur in less than 5% of all cases of dengue, however those who have previously been infected with other serotypes of dengue virus ("secondary infection") are at an increased risk.

 DIAGNOSIS:-

             The diagnosis of dengue is typically made clinically, on the basis of reported symptoms and physical examination; this kind of diagnosis is especially carried in endemic areas. However, early disease can be difficult to differentiate from other viral infections. General diagnosis is based on the findings of fever  nausea and vomiting, rash, generalized pains, low white blood cell count, positive tourniquet test, in someone who lives in anendemic area. The diagnosis should be considered in anyone who develops a fever within two weeks of being in the tropics or subtropics. It can be difficult to distinguish dengue fever and chikungunya, as both the viral infection shares many symptoms and occurs in similar parts of the world to dengue. Often, investigations are performed to exclude other conditions that cause similar symptoms, such as malaria, leptospirosis, viral hemorrhagic fever, typhoid fever,  measles, and influenza.

                The earliest change detectable in laboratory testing is a low white blood cell count, which may then be followed by low platelets and metabolic acidosis. A moderately elevated level of aminotransferase from the liver is commonly associated with low platelets and white blood cells. 

             Dengue fever may be diagnosed by microbiological laboratory testing. This can be done by virus isolation in cell cultures, nucleic acid detection by PCR, viral antigen detection or specific antibodies. Virus isolation and nucleic acid detection are more accurate than antigen detection, but these tests are not widely available due to their greater cost.

             Tests for dengue virus-specific antibodies, types IgG and IgM, can be useful in confirming a diagnosis in the later stages of the infection. Both IgG and IgM are produced after 5–7 days. The highest levels of IgM are detected following a primary infection. After a primary infection the IgG reaches peak levels in the blood after 14–21 days. Both IgG and IgM provide protective immunity to the infecting serotype of the virus.

PREVENTION AND CONTROL:- 

- There are no approved vaccines for the dengue virus. 

-Prevention thus depends on control and protection from the bites of the mosquito that transmits it. 

-Elimination of stagnant water at home, schools and work place to avoid breeding of mosquitoes. 

-Using insect repellents over the exposed parts of the body.Using mosquito screens or nets in non – air-conditioned rooms. 

-Wearing the long sleeved clothes like long trousers of a light shade for protection against mosquitoes.

-Properly covering all water tanks so that mosquitoes cannot get in. Getting rid of any container capable of retaining water in the outdoor surroundings (used tyres, food cans, garbage, saucers under flower pots, etc).

- Renew water in flower vases at least once a week. Aedes species is the main target of control. Source reduction of breeding sites of mosquitoe. 

-Requires community involvement to keep the water storage containers free of mosquitoes. Eliminate other breeding places in and around houses. 

-Introduction of larvivorous fish, namely Gambusia and Guppy in water tanks and other water sources. -

-The organophosphorous insecticide ABATE is being used in a large scale. ABATE can prevent breeding upto 3 months when applied to sand granules. It does not affect man or the taste of water. 

-Educate community about the disease, mode of its transmission, availability of treatment and adoption of control measures.

-Changes in practice of storage of water and personal protection should be encouraged. They should also be reassured that this a preventable disease. 

-Community should be advised to cooperate in fogging. Take measures for eliminating breeding places. Special campaigns may be carried out involving mass media including local vernacular newspapers/magazines, radio and TV as well outdoor publicity like hoardings, miking, drum beating, rallies etc. 

-Health education materials should be developed and widely disseminated in the form of posters, pamphlets, handbills. 

-Interpersonal communication through group meetings, traditional/folk media particularly must be optimally utilized.

EPIDEOMOLOGY :-