KATHMANDU

Dengue, the most common arbovirus infection worldwide, has become serious public health concern. As of today the geographic distribution of dengue has crossed more than 100 countries.

The World Health Organisation has estimated that more than 2.5 billion people are at risk of dengue infection.

Dengue is a mosquito-borne viral disease mostly reported on tropical or sub-tropical areas.

In the context of Nepal, the dengue incidence has increased rapidly in recent years due to expansion of vector (Aedesaegypti and Aedesalbopictus) and fewer cases being imported from the movement of people from the affected regions, mostly from India.

Transmission of dengue

Dengue is transmitted primarily by the bite of female Aedesaegypti mosquito. The mosquito is highly anthropophilic in nature and gets attracted to humans rather than other animals. This specific mosquito has short and frequent biting behaviour. It prefers to rest indoors, and the mosquito bites usually during day time. Its peak biting periods are early morning and before dusk.

Aedesaegypti mosquito has specific arc on the thorax region, ornamented with white stripes and spots on its body and appendages except wings.

Once infected, humans are the main carriers and multipliers of the virus, serving as the source of virus for the uninfected mosquitoes.

Incubation period varies from three to 14 days.

Clinical features

Dengue viral infection usually shows mild symptoms of fever and flu-like features. Dengue infections are primarily categorised into two main types.

• Dengue fever

• Dengue haemorrhagic fever

Dengue fever

The illness starts from two to seven days of infection. The most common symptoms of dengue fever are:

• High fever(102 – 105 degrees F)

• Aches and pain: Headache, pain behind the eyeball, muscle pain, joint pain

• Loss of appetite

• Nausea and vomiting

• Abdominal discomfort

• Dehydration

• Swollen glands

• Electrolyte imbalance

• Skin rashes et cetera

Dengue haemorrhagic fever

This is the severe /critical form of dengue viral infection. People with history of dengue infection are prone to developing severe from of dengue. Infants and pregnant women are at higher risk of developing dengue haemorrhagic fever.

The symptoms of dengue haemorrhagic fever usually start within 24 to 48 hours of infection. The common symptoms are:

Leucopenia and thrombocytopenia: Significant decrease in white blood cells and platelets leads to plasma leakage.

Haemorrhagic stage: Decrease in platelets leads to internal bleeding - abdominal bleeding, blood in urine, stool, and vomit, bleeding from nose and gums.

In severe form of dengue, organ impairment may occur such as, Hepatitis, encephalitis or myocarditis.

Diagnosis

Mortality from dengue can be reduced to almost zero by implementing timely, appropriate clinical management, which involves early clinical and laboratory diagnosis.

A successful clinical outcome requires efficient and early diagnosis of cases provided by accurate differential diagnosis, rapid laboratory assessment/confirmation, and early response to severe disease.

Diagnostic tests - complete blood cell count, detection of viral nucleic acid, detection of viral antigen and antibodies can help in the diagnosis of dengue infection. Invitro diagnostic test kits are easily available for the identification.

Prevention and control

Dengue mortality can be reduced by implementing early case detection and appropriate management of severe cases, reorienting health services to identify early cases and manage dengue outbreaks effectively.

Control of dengue vectors can be done mainly by source reduction - the elimination of containers that are favourable sites for oviposition and development of the aquatic stages. Insecticides can be sprayed on the surface of stagnant water to kill the aquatic stages of mosquito.

The availability of a safe, efficacious and cost-effective vaccine would significantly alter the concept for dengue prevention. Some live-attenuated vaccines going through different stages of clinical trials might be available for public in the near future.

(The author is medical laboratory scientist, medical microbiologist)

A version of this article appears in the print on September 10, 2022 of The Himalayan Times.