Dengue Fever

Dengue

• Caused by any of four closely related dengue viruses

  • DENV 1, 2, 3, 4

• Transmitted by Aedes aegypti and Aedes albopictus

• An estimated over 100 million cases of Dengue worldwide each year

• The most important mosquito-borne viral disease in the world

• In the last 50 years, the incidence has increased 30-fold

• 2.5 billion people live in over 100 endemic countries

• 50 million infections occur annually

  • 500,000 cases of DHF

  • 22,000 deaths, mainly among children

Principal Vector

• Aedes albopictus

• Aedes Aegypti

Aedes Behavior

• Usually bred in stagnant water

• Usually active in dark or shaded places outdoors, but indoor activity is also possible

• Distance of flight: less than 100 meters

• Most active: 2 hours before sunset (5-6 pm) and morning (8-9 am)

Life Cycle of the Virus

1. The virus is inoculated into humasn with the mosquito saliva

2. The virus localizes and replicated in various target organs, for example, local lymph nodes and the liver

3. The virus is then released from these tissues and spreads through the blood to infect WBC and other lymphatic tissues

4. The virus is then released from these tissues and circulated in the blood

5. The mosquito ingests blood containing the virus

6. The virus replicates in the mosquito midgut, the ovaries, nerve tissue, and fat body. It then escapes into the body cavity, and later infects the salivary glands

7. The virus replicates in the salivary glands and when the mosquito bites another human, the cycle continues

Dengue Fever Symptoms

• Fever: continuous for 3 to 7 days

• Severe headache

• Joint pain, muscle pain, pain behind the eyes

• Nausea, vomiting, and rash

• Mild bleeding

Dengue Hemorrhagic Fever

• Fever that lasts 2-7 days

• When the fever declines, symptoms include:

  • Persistent vomiting, severe abdominal pain, and difficulty breathing

  • Capillaries become excessively permeable, allowing the fluid component to escape from the blood vessels into the peritoneum and pleural cavity. This may lead to failure of the circulatory system and shock, followed by death.

  • A patient with DHF has a low platelet count and hemorrhagic manifestations, a tendency to bruise easily or other types of skin hemorrhages, bleeding nose or gums, and possibly internal bleeding

Four grades of hemorrhagic fever

• Grade 1

  • Fever and nonspecific symptoms

  • A positive tourniquet test is only a hemorrhagic manifestation

• Grade 2

  • Grade 1 manifestations and spontaneous bleeding

• Grade 3

  • Signs of circulatory failure (rapid/weak pulse, narrow pulse pressure, hypotension, cold/clammy skin)

• Grade 4

  • Profound shock: (Undetectable pulse and BP)

Dengue Fever - Treatment

• At present, no specific drug that can treat

• The patient should be isolated in a mosquito-free environment to prevent the spread of disease

• For DHF, medical care by physicians and nurses experienced with the effects and progression of the complicating hemorrhagic fever can frequently save lives, decreasing mortality rates from more than 20% to less than 1%

• Maintenance of patients’ circulating fluid volume is the central feature of DHF care

Immunity

• Immunity is gained against that serotype after recovery from its infection. However, no effective protection is conferred against infection, by the other three serotypes

• If the patient is infected with the other three different serotypes, it will increase the risk of getting DHF

Dengue Outbreaks

• During the 19th century, dengue was considered a sporadic disease

• Before 1970, only 9 countries had experienced cases of DHF. Since then, the number has increased more than 4-fold and continues to rise

Transatlantic Slave Trade

• A pandemic in 1998

  • 1.2 million cases of DF and DHF were reported from 56 countries worldwide

  • Unprecedencted

  • In 2001, the Americas alone reported

    • Over 652,212 cases of dengue

    • 15,00 were DHF

    • Nearly double the cases reported for the same region in 1995

  • The challenge for national and international health agencies is to reverse the trend of increased epidemic dengue activity and increased incidence of DHF

Why is this happening?

• In countries where transmission does routinely occur, short-term changes in

  • Temperature, precipitation, and humidity are often correlated with dengue incidence

• Other Factors:

  • The interplay of the four different Dengue serotypes

  • Urbanization

  • Urbanization

  • Lack of sanitation

  • Increased long-distance travel

  • Ineffective mosquito control

  • Increased reporting capacity

Dengue changes mosquito behavior

• Disease-infected mosquitoes were found to fly around more than uninfected mosquitoes, increasing their ability to spread chronic and deadly diseases

  • Like being on caffeine

Article Discussion

• Wolbachia pipientis are bacteria that infect a wide range of invertebrates, mainly arthropods and numerous insects

• Wolbachia is one of the most common pathogens on Earth that infects the reproductive system of insects; it is estimated that more than 18% of insects are infected by it

  • Male killing (death of infected males)

  • Feminization (infected males grow as either fully fertile females or infertile pseudo-females)

  • Parthenogenesis (reproduction of infected females asexually)

  • Cytoplasmic incompatibility (the inability of Wolbachia- infected males to successfully reproduce with uninfected females)