diease

Dengue


OVERVIEW OF Dengue :

Dengue virus is a vector borne disease. Mosquitoes acts as an important vector in transmitting this disease.


STRUCTURE of Dengue :

The dengue virus family belongs to the Flaviviridae,

Flaviviridae

 

    1. Morphology
      • Viruses of Flaviviridae family are Spherical viruses.
      • Size: 40 – 50 nm in diameter.
      • Genetic Material : (+) ssRNA.

            Classification

    • Some members of Flaviviridae are Mosquito-borne while others are Tick-borne
    • Hepatitis C virus is neither mosquito nor tick-borne.
    • Mosquito-borne Flaviviruses
      1. Encephalitis viruses
        1. St. Louis Encephalitis Virus
        2. Ilheus Virus
        3. West Nile Virus
        4. Murray Valley Encephalitis Virus
        5. Japanese B Encephalitis Virus
      2. Yellow Fever
      3. Dengue
    • Tick-borne Flaviviruses
      1. Tick-borne Encephalitis viruses
        1. Russian Spring-Summer Encephalitis
        2. Powassan Virus
      2. Tick-borne Hemorrhagic Fevers
        1. Kyasanur Forest disease (KFD)
        2. Omsk Hemorrhagic fever


CAUSES :

Dengue viruses are spread to the people through the bite of the infected aedes species mosquitoes (Ae. aegypti or Ae. albopictus). These are the same type of viruses that causes the Zika and chikungunya viruses.

The mosquitoes most probably lay eggs near the standing/stagnant water in container that hold water, like buckets, bowls, animal dishes, flower, pots and vases.

These mosquitoes prefer to bite peoples and live both indoors and outdoors near people.

Mosquitoes that spread dengue, chikungunya and zika bite during the day and night.

Mosquitoes become infected when they bite a person infected with the virus. Infected mosquitoes can then spread the virus to other people through bites.

It also can spread by vertical transmission, that is from the mother to the child.

If a pregnant woman already infected with the dengue can pass the virus to the foetus during the pregnancy or around the time of birth.

It also can spread through infected blood, laboratory or healthcare setting exposures.

Rarely in cases with organ transfusions, the dengue might shows it spread.

 


PATHOPHYSIOLOGY :

When the mosquitoes bites the healthy person, the virus enters into the skin and reach the specialized immune cells of the skin called as Langerhans cells. The virus tends to replicates and infects the Langerhans cells of the skin. Langerhans cells releases the interferons to limit the spread of the infection. These infected Langerhans cells then passes to the immune system to create alertness in the host immune cells. Then these cells passes to the blood stream and result in viremia.

Activation of the immune cells results in increase in the lymphocyte count. Decrease in the neutrophils and the white blood cell count is also seen. These mechanism result in the release of pyrogens and increases the blood pressure leading to the formation of the rashes and other clinical manifestations of the dengue.

Primary manifestation of the disease include capillary leak syndrome( plasma leakage due to DHF specific endothelial cell dysfunction), thrombocytopenia( seen in all types of DENV infection, but ectreme in DHF), hemorrhagic tendencies and leukopenia. It is also known that the major envelope present in the virus aids them in the attachment of the virus with host cells. Studies suggest that the viruses primarily target the monocytes. Activation of the monocytes results in the release of interferon alpha and interferon beta. The envelope protein present in the virus that is the protein ‘E’ aids in the attachment and also acts as a protective factor to the virus. Studies suggest that dengue virus specific CD4+ and CD8+ lymphocytes attacks the infected cells and releases interferon (INF), tumour necrosis factor alpha(TNF-a) and lymphotoxin. Primary infection induces a lifetime immunity of the individual to that particular serotype, but not to secondary infection by another serotype.

 


ROUTES OF TRANSMISSION :

The virus is a vector borne virus. The virus is transmitted by the mosquitoe aedes aegypti


COMMON CLINICAL SIGNS AND SYMPTOMS :

The symptoms starts 4-10 days after the infection with the virus.

Dengue fever causes a high fever — 104 F (40 C) — and any of the following signs and symptoms:

  • Headache
  • Muscle, bone or joint pain
  • Nausea
  • Vomiting
  • Pain behind the eyes
  • Swollen glands
  • Rash

Sever symptoms might include:

  • Severe stomach pain
  • Persistent vomiting
  • Bleeding from your gums or nose
  • Blood in your urine, stools or vomit
  • Bleeding under the skin, which might look like bruising
  • Difficult or rapid breathing
  • Fatigue
  • Irritability or restlessness


DIAGNOSTIC :

Complete blood test:

The blood test might shows the decreased level of platelet counts and other immune cells. Thrombocytopenia( decrease in the platelet count) might increases the chances for bleeding tendencies.

Nucleic acid amplification tests (NAATs):

For the patient diagnosed with the dengue virus, NAAT’s are the preferred method of laboratory diagnosis:

NAATs should be performed on serum specimens collected 7 days or less after symptom onset.

Laboratory confirmation can be made from a single acute phase serum specimen obtained early ( less than 7 days after the fever onset in the illness by detecting viral genomic sequences with Rrt-pcr or non structural proteins 1 (NS1) antigen by immunoassay.

Presence of virus by Rrt-PCR or NS1 antigen in a single diagnostic specimen is considered as laboratory confirmation test.

Serological tests:

IgM antibody testing can identify additional infections and it is an important diagnostic tool.

Later in the illness greater than 4 days after onset of the fever, IgM against dengue virus can be detected with MAC-ELISA. For patients presenting with the symptoms during the first week diagnostic test should include a test for dengue virus (Rrt-PCR or NS1) and IgM.

For patients presenting grater than 1 week after fever onset, IgM detection is most useful.

IgM in a single serum sample strongly suggests a recent dengue virus infection and it can be taken as a probable confirmatory test.

IgG antibody testing

IgG detection by ELISA in a single serum sample is not useful for diagnostic testing because it remains detectable for life after a dengue virus infection.

Detection of virus-neutralizing antibodies in combination with recent travel history to an

endemic area may be meaningful.

Immunosorbent assay- detect the virus specific IgM or IgG antibodies.

Greater than fourfold rise in titer between acute and convalescent sera and cerebo spinal

fluid containing virus specific IgG or IgM or both are the diagnostic features.

Mouse suckling:

This test involves the injection of arbovirus in to the mice cell by suckling action. Later the mice are checked for the symptoms and other features.

 


TREATMENT AND PROGNOSIS :

The primary prescribed medicine is acetaminophen or paracetomol.

Non steroidal anti inflammatory drugs should be avoided that it might result in the thinning of blood and promotes bleeding tendencies.

Fluid intake is must


PROGNOSIS :

The dengue is a deadly disease when it is left untreated.

The recovery percentage of the disease include 20-50%.

Recovery period:

After the treatment with certain medications the recovery time is 2-3 weeks.

Medicines:

Actetoaminophen

Paracetomol


PREVENTION :

  • Clean the stagnant area which host for multiplication of virus.
  • Wear clothing that covers the arms, legs, and feet whenever you are outdoors.
  • Use mosquito repellents sparingly on exposed skin. An effective repellent will contain 20% to 30% DEET (N,N-diethyl-meta-toluamide).
  • Spray clothing with repellents containing permethrin or DEET as mosquitoes may bite through thin clothing.
  • Take plenty of fluids
  • Follow healthy life style
  • Minimize outdoor activities at dawn, dusk, and in the early evening when mosquitoes are most active.
  • Inspect window and door screens and repair any holes found.


Medicines used in the Treatment :

Acetaminophen

Paracetomol