Kolkata is reeling under its worst bout of dengue this monsoon season. Many people have succumbed to the infection and government and private hospitals are flooded with dengue patients. (1) The city is facing one of its worst dengue outbreaks in recent times.
Nine-year old Sreeja Das was the first dengue victim in the state. The epidemic first struck in the second week of August.Several people in and around Kolkata have been hospitalized since then with symptoms similar to dengue. Many patients have died from the disease and the number of confirmed cases has gone up to 638 (2) and still counting.
Dengue is a Public Health Menace which is better prevented rather than being treated as is the case with all diseases.
There has been a recent surge in Dengue cases not only in Kolkata, but in various other parts of the world as well. The incidence of dengue has grown dramatically around the world in recent decades. Over 2.5 billion people (i.e. over 40% of the world's population) are now at risk from dengue. WHO currently estimates that there may be 50–100 million dengue infections worldwide every year (3) .
Dengue also known as breakbone fever, is an infectious tropical disease caused by the dengue virus (4) . There are four distinct, but closely related, serotypes of the virus that cause dengue (DEN-1, DEN-2, DEN-3 and DEN-4). Recovery from infection by one provides lifelong immunity against that particular serotype. However, cross-immunity to the other serotypes after recovery is only partial and temporary. Subsequent infections by other serotypes increase the risk of developing severe dengue (3) .
Dengue is transmitted by the Aedes aegypti mosquito which is the primary vector of dengue. The virus is transmitted to humans through the bites of infected female mosquitoes. 4–10 days after getting infected, a mosquito is capable of transmitting the virus for the rest of its life. Infected humans are the main carriers and multipliers of the virus, serving as a source of the virus for uninfected mosquitoes (3) .
The Aedes aegypti mosquito lives in urban habitats and breeds mostly in man-made containers. Ae. aegypti is a daytime feeder; its peak biting periods are early in the morning and in the evening before dusk. Female Ae. aegypti bites multiple people during each feeding period (3) .(Also called Fearless Day Biter.)
The rapid transmission of the dengue virus this year in Kolkata has led experts to believe that a new vector is stalking the city along with the primary carrier Aedes aegypti, especially in Salt lake, the fringe areas of the city and along the EM Bypass where hundreds have been infected. Aedes albopictus or the Asian tiger mosquito is a secondary vector of the dengue virus and as lethal as the Aedes aegypti. (5) . Aedes albopictus has also spread to North America and Europe largely due to the international trade in used tyres (a breeding habitat) and other goods (e.g. lucky bamboo). Ae. albopictus is highly adaptive and therefore can survive in cooler temperate regions of Europe. Its spread is due to its tolerance to temperatures below freezing, hibernation, and ability to shelter in microhabitats (3) .
Rampant construction activities and chopping of trees along the Bypass (Kolkata) are responsible for a spurt in the number of tiger mosquitoes this year. The albopictus prefers old buildings and tree crevices. With buildings being pulled down for high-rises and trees being chopped to make way for the Garia-Dum Dum Metro corridor along Bypass, the secondary vector has turned active. More than 1500 trees have been felled along the Bypass since 2010 to make way for Metro pillars. Green activists believe this has upset the ecosystem of the area and contributed to the spread of diseases like malaria and dengue (5) .
Albopictus mosquito rests in the vicinity of human dwellings. They tend to move into houses quicker than other vectors and are hence more difficult to eliminate (5) .
A case of dengue may present as (6) :
- Classical dengue fever
- Dengue haemorrhagic fever
- Dengue shock syndrome
Classical dengue fever: Dengue fever can occur in epidemics which often start during the rainy season when the breeding of the vector mosquitoes is generally abundant.
All ages and both sexes are susceptible to dengue fever. Children usually have a milder disease than adults. The onset of the disease is sudden with chills and high fever, intense headache, muscle and joint pains. There may be pain behind the eyes (Retro orbital pain).
Other common symptoms include extreme weakness, anorexia, constipation, altered taste sensation, pain in abdomen, sore throat and general depression.
Fever is usually between 39°C and 40°C and is associated with generalized pain and a headache; this usually lasts two to seven days. At this stage, a rash occurs in 50–80% of those with symptoms. It occurs in the first or second day of symptoms as flushed skin, or later in the course of illness (days 4–7), as a measles-like rash (4) . The Rash starts on the chest and back and may spread to the extremities and rarely to the face. It may be accompanied by itching and hyperaesthesia. The rash lasts for 2 hours to several days and may be followed by desquamation (6) .
Recovery is usually complete (6) .
Dengue haemorrhagic fever: Dengue haemorrhagic fever (DHF) is a severe form of dengue fever, caused by infection with more than one dengue virus. The severe illness is thought to be due to double infection with dengue viruses - the first infection probably sensitizes the patient, while the second appears to produce an immunological catastrophe. It presents with the following clinical manifestations :
(a) Fever - acute onset, high, continuous, and lasting 2 to 7 days.
(b) Haemorrhagic manifestations like petechiae, purpura, ecchymosis, epistaxis, gum bleeding haematemesis and/or melaena.
(c) Enlargement of liver.
Blood examinations reveal Thrombocytopenia (Platelet count 100,000/mm3 or less).
And Haemoconcentration (haemotocrit increased by 20 per cent or more of base-line value.)
Dengue shock syndrome (DSS): It is DHF (Dengue Haemorrhagic fever) plus Shock-manifested by rapid and weak pulse with narrowing of the pulse pressure (20 mm Hg or less) or hypotension, with the presence of cold, clammy skin and restlessness.
The diagnosis of dengue is typically made clinically, on the basis of reported symptoms and physical examination. A doctor should be consulted immediately if any of the symptoms as mentioned above appears especially in as endemic area or if the zone is under an ongoing epidemic. The warning signs of Dengue involve Abdominal pain Ongoing vomiting, Liver enlargement, Mucosal bleeding, High hematocrit with low platelets and lethargy (7) .
The diagnosis should be considered in anyone who develops a fever within two week of being in the tropics or subtropics. The earliest change detectable on laboratory investigations is a low white blood cell count, which may then be followed by low platelets and metabolic acidosis (4) .
Dengue fever may be diagnosed by microbiological laboratory testing (7) . This can be done by virus isolation in cell cultures, nucleic acid detection by PCR, viral antigen detection or specific antibodies (serology) (8) . Virus isolation and nucleic acid detection are more accurate than antigen detection, but these tests are not widely available due to their greater cost (7) . All tests may be negative in the early stages of the disease (8) . PCR and viral antigen detection are more accurate in the first seven days (9) .
There are no specific treatments for dengue fever. Treatment depends on the symptoms, varying from oral rehydration therapy at home with close follow-up, to hospital admission with administration of intravenous fluids and/or blood transfusion (4) . A decision for hospital admission is typically based on the presence of the "warning signs" discussed above, especially in those with preexisting health conditions.
Dengue Shock Syndrome is a medical emergency that requires hospitalization with prompt and vigorous volume replacement therapy (6) . Blood transfusion is initiated early in patients presenting with unstable vital signs in the face of a decreasing hematocrit, rather than waiting for the hemoglobin concentration to decrease to some predetermined "transfusion trigger" level (7) .
The juice of the papaya leaf has been seen to arrest the destruction of platelets that has been the cause for so many deaths from dengue. Chymopapin and papin - enzymes in the papaya leaf - help revive platelet count. The juice has to be prepared from fresh papaya leaves (10) .
Prevention of Dengue infection depends on control of and protection from the bites of the mosquito that transmits it. The vectors of DF and DHF (e.g., A. aegypti) breed in areas around houses and, in principle can be controlled by individual and community action, using various mosquito control measures (6) . (The primary method of controlling A. aegypti is by eliminating its habitat. This is done by emptying containers of water or by adding insecticides or biological control agents to these areas.
The personal protection measures are like that of wearing of full sleeve shirts and full pants; use of mosquito repellent cream; liquids, coils, mats etc.; use of bed-nets for sleeping infants and young children during day time to prevent mosquito bites. So far, there is no satisfactory vaccine and no immediate prospect of preventing the disease by immunization. (6) .
The World Health Organization recommends an Integrated Vector Control program consisting of five elements to fight this menace:
- Advocacy, social mobilization and legislation to ensure that public health bodies and communities are strengthened,
- collaboration between the health and other sectors (public and private),
- an integrated approach to disease control to maximize use of resources,
- evidence-based decision making to ensure any interventions are targeted appropriately
- capacity-building to ensure an adequate response to the local situation
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