Dengue is a flu like viral illness caused by any of the four types of dengue virus (DEN-1 to 4). A potentially lethal disease that affects 50 million people per year. It is transmitted to humans through bites of female Aedes aegypti mosquitoes. Mosquito acquires virus from feeding on infected person’s blood and it incubates virus for 8-10 days. Virus circulates in blood of humans for two to seven days. Dengue is found in tropical and sub-tropical areas worldwide, predominantly in urban and semi-urban areas. Southeast Asia and Western Pacific the most seriously affected areas.

Symptoms: Fever, Vomiting, Muscle & Joint Pains, Unexplained heavy bleeding, Body Rashes, Severe Headache etc. Dengue fever, also known as breakbone fever, is a mosquito-borne tropical disease caused by the dengue virus. “International Anti-Dengue Day is observed every year on June 15th”.

Dengue Fever symptomsDengue Symptoms

DENGUE FEVER TYPES
1) Breakbone Fever
2) Dandy Fever
3)Dengue Hemorrhagic Fever
4)Dengue Shock Syndrome
5)Duengero
6)Seven Day Fever, Dengue Type

GLOBAL BURDEN ON DENGUE FEVER:
The incidence of dengue has grown dramatically around the world in recent decades. The actual numbers of dengue cases are under reported and many cases are misclassified. One recent estimate indicates 390 million dengue infections per year (95% credible interval 284–528 million), of which 96 million (67–136 million) manifest clinically (with any severity of disease). An estimated 50 million people with severe dengue require hospitalization each year, a large proportion of whom are children. About 2.5% of those affected die.

HISTORY: The first record of a case of probable dengue fever is in China (265–420 AD) they referred it as “water poison” associated with flying insects. Early reports of dengue epidemics are from 1779 and 1780, when an epidemic swept across Asia, Africa and North America. From that time until 1940, epidemics were infrequent. In 1906, transmission by the Aedes mosquitoes was confirmed, and in 1907 dengue was the second disease (after yellow fever that was caused by virus. The marked spread of dengue during and after the Second World War has attributed to ecologic disruption. Dengue hemorrhagic fever and dengue shock syndrome were first noted in Central and South America in 1981, as DENV-2 was contracted by people who had previously  been infected with DENV-1 several years earlier.

VIROLOGY: Dengue is a mosquito-borne viral disease that has rapidly spread in all regions of WHO in recent years. Dengue virus is transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, A. albopictus. The disease is widespread throughout the tropics, with local variations in risk influenced by rainfall, temperature and unplanned rapid urbanization.

Dengue fever virus (DENV) is an RNA virus of the family Flaviviridae; genus Flavivirus usually transmitted by arthropods (mosquitoes or ticks), and hence  referred to as arboviruses (arthropod-borne). There are 5 strains of the virus, called serotypes based on their antigenicity.They are referred to as DENV-1, DENV-2, DENV-3 and DENV-4. The fifth type was announced in 2013.

MODES OF TRANSMISSION: Dengue virus is primarily transmitted by female Aedes mosquitoes, particularly A. aegypti. They typically bite during the day,  particularly in the early morning and in the evening. Other  Aedes species that transmit the disease include    A. albopictus, A. polynesiensis and A. scutellaris. Humans are the primary host of the virus but it also circulates in nonhuman primates.

Dengue TransmissionDengue Fever cases

1) HOW DOES THE INFECTION SPREADS THROUGH
MOSQUITOES: A female mosquito that takes a blood meal from a person infected with dengue fever, during the initial 2–10 day febrile period, becomes itself infected with the virus in the cells lining its gut. About 8–10 days later, the virus spreads to other tissues including the mosquito’s salivary glands and is subsequently released into its saliva. The virus seems to have no detrimental effect on the mosquito, that remains infected for life. Aedes aegypti is particularly involved, as it prefers to lay its eggs in artificial water containers, to live in close proximity to humans, and to feed on people rather than other vertebrates.
2) Dengue can also be transmitted via infected blood products and through organ donation.
3) Vertical transmission (from mother to child) during pregnancy or at birth.
4) person-to-person.

PREDISPOSITION: 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.

MECHANISM: 1)The virus binds to and enters white blood cells, and reproduces inside the cells while they move throughout the body. The white blood cells respond by producing a number of signaling proteins( cytokines and interferons). 2) Fluid from the bloodstream leaks through the wall of small blood vessels into body cavities due to capillary permeability {reduced blood supply may damage vital organs}. 3) Dysfunction of the bone marrow due to infection of the stromal cells leads to reduced number of platelets.

SIGNS & SYMPTOMS: Dengue fever is a severe, flu-like illness that affects infants, young children(USUALLY WELL NOURISHED) and adults, but seldom causes death. Symptoms usually last for 2–7 days, after an incubation period of 4–10 days after the bite from an infected mosquito.
The course of infection is divided into three phases:
1) febrile, 2) critical, 3) recovery.

1) FEBRILE PHASE: a) Sudden onset high fever 40 °C (104 °F) usually lasts for 2-7 days. (biphasic or saddle like nature)

a) Hypotension{depletion of fluids from circulation leading to reduced blood supply}
b) Ascites
b) Headache
c) Plural effusion {fluid accumulation in chest and abdominal cavities}
c) Bleeding from nose and mouth(due to mucous membrane damage)
d) Nausea, vomiting
d) Dengue Haemorrhagic Fever (DHF): DF symptoms+ some of following
e) Diarrhoea
e) Dengue shock syndrome (DSS): dengue hemorrhagic fever plus:
f)  Muscle & joint pains
g) Rash 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 (islands of white in a sea of red).

2) CRITICAL PHASE: The disease proceeds to a critical phase as fever resolves.

1) Severe and continuous pain in abdome
2) Bleeding from the nose, mouth and gums or skin bruising
3) Frequent vomiting with or without blood
4) Black stools, like coal tar
5) Excessive thirst (dry mouth)
6) Pale, cold skin
7) Restlessness, or sleepiness

  • Weak rapid pulse
  • Narrow pulse pressure (less than 20 mm Hg)
  • Cold, clammy skin and restlessness.

3) RECOVERY PHASE: Usually lasts two to three days with resorption of the leaked fluid into the bloodstream.

a) Severe itching
b) Slow heart rate.
c) Rash (maculopapular or a vasculitic appearance,followed by peeling of skin)
d) Reduced level of consciousness or seizures.
e) Fatigue may last for weeks in adults.

DIAGNOSIS: Usually based on
1) clinical symptoms plus
2) Warning signs:

  • Worsening abdominal pain
  • Ongoing vomiting
  • Liver enlargement
  • Mucosal bleeding
  • High hematocrit with low platelets
  • Lethargy or restlessness
  • Serosal effusions

3) The tourniquet test: It involves the application of a blood pressure cuff at between the diastolic and systolic pressure for five minutes,    followed by the counting of any petechial hemorrhages; a higher number makes a diagnosis of dengue more likely with the cut off being more than 10 to 20 per 1 inch 2 (6.25 cm2).

4) Lab reports:  Low platelets metabolic acidosis elevated level of amino transferase (AST and ALT) rising hematocrit and       hypoalbuminemia

5) Ultrasound: Fluid check

6) pulse pressure: (DSS) drops to ≤ 20 mm Hg plus peripheral vascular collapse

TREATMENT:

  • No specific medicine except for symptomatic relief.
  • Pain relievers such as aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) should only be taken under a doctor’s supervision  because of the possibility of worsening bleeding complications.
  • Acetaminophen (Tylenol) and codeine may be given for severe headache and for joint and muscle pain (myalgia).
  • Take plenty of fluids.

PREVENTION: 
Self protection: Stay away from heavily populated residential areas. Use mosquito repellents, even indoors. maintain clean surroundings and follow good habits.
Eliminating Habitats: Generalized spraying with organophosphate or pyrethroid insecticides. Mosquito netting while resting the application of insect repellent (DEET being the most effective) To reduce the mosquito population, get rid of places where mosquitoes can breed. These include old tyres, cans, or flower pots that collect rain. Regularly change the water in outdoor bird baths and pets’ water dishes. Be aware of Dengue fever.

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