Medical Fun Facts Podcast

MFF0077: Dengue virus infection

It’s Monday 31 July 2017.

Last week I did Cryptococcus. Tonight, as we progress again through the alphabet I thought about Dengue fever and Dengue virus.

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The Dengue virus is in the genus Flavivirus which also includes Zika virus and Yellow fever virus. The Dengue virus is a single-stranded RNA virus transmitted to humans by mosquitoes. Dengue virus is also known as an arbovirus or arthropod-borne virus.

Unlike some other Flavivirus infections, human infection with Dengue virus, Yellow fever virus and Zika virus are not incidental because when infected, our cells produce enough replicated virus for a mosquito to carry it to other humans without the need for other animals to be involved.

Within the species Dengue virus, five serotypes exist.

Until a few hundred years ago, the Dengue virus was transmitted within nonhuman primates and Ædes mosquitoes, with humans as a dead-end host. Now, the transmission cycle is exclusively between these mosquitoes and humans.

Dengue fever is the disease caused by Dengue virus. The disease occurs after a mosquito carrying Dengue virus bites a human and infects the human through the bite site. Symptoms begin to appear between three and fourteen days after infection. The usual symptoms include fever, headache, vomiting, muscle and joint pain, along with a skin rash. It usually takes a week before a patient begins to feel better. In a small number of patients, the disease progresses to Dengue hæmorrhagic fever. Dengue hæmorrhagic fever is characterised by bleeding, an abnormally low platelet count, and blood plasma leakage. When the patient’s blood loss is extreme and their blood pressure falls dramatically, the patient is said to be in Dengue shock.

While infection with one of the five serotypes typically confers life-long immunity to that type and partial immunity to the other types, when infection occurs with another serotype, the complex immunological reactions are thought to give rise to Dengue hæmorrhagic fever as a complication of the less severe Dengue fever.

Several methods have been devised to reduce infection. These include simple measures to avoid mosquitoes plus some vaccines which are currently being investigated. In Australia, work is being done on biological control measures including the use of the bacterium Wolbachia. The notion being that Wolbachia infected mosquitoes are resistant to infection with Dengue virus.

Diagnosis is often made clinically in the tropics and subequatorial areas where Dengue fever and the mosquitoes that carry Dengue virus are endemic.

Patients often have nausea and vomiting plus a low white cell count, and clinical evidence of a low platelet count like petechial hæmorrhages. The earliest changes in laboratory test parameters include a low white blood cell count.

Specific diagnostic tests include direct detection of the NS1 protein or Dengue virus antibodies. PCR tests are also available.

There is no specific treatment for Dengue fever. It’s important not to use drugs that inhibit platelet aggregation like aspirin and nonsteroidal antiinflammatory drugs.

I’ve seen two patients die while infected with Dengue virus. Unfortunately, one patient was given a nonsteroidal antiinflammatory drug which lowered his platelet count to 8 and he bled out. In my mind that was an avoidable death.

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