April 22, 2014
Article by Global Pre-Meds
Hospital doctor shadowing & global health experience programs.
While Malaria, a well-known parasitic disease spread by mosquitos, has caught the world’s attention, another not so famous deadly mosquito-borne infection is rapidly spreading.
Dengue is now the leading cause of death and illness for people living in tropical and subtropical areas. WHO reports that more than 40% of the world’s population lives in dengue affected zones, and conservatively estimate that 50-100 million people are infected worldwide each year.
The virus only emerged as a worldwide problem in the 1950’s, but is now endemic. There is no vaccination available and only supportive treatment such as rehydration in mild cases and blood transfusions in severe cases is offered to those infected. While dengue cases are rare in the USA, the UK, Europe, Australia and Russia, the virus is widespread in Central and South America, South-East Asia, Africa and the Pacific. However, increasing global temperatures have meant that both dengue and malarial zones are now expanding.
Dengue is carried by the female Aedes aegypti and Aedes albopictus mosquitos that live in tropical and sub-tropical climates under 1000 metres/3300 feet in altitude. Infected mosquitos transmit the virus to humans through bites. They typically bite during the day, especially near dawn and dusk, and are infectious all year round. Humans are the main multipliers of the virus. Patients who have dengue can carry the infection for up to 12 days after their symptoms appear and transmit the virus to otherwise non-affected mosquitos as they bite the patient. The virus incubates in the mosquito for 4-10 days before being released into the mosquito’s saliva where is becomes infectious to bitten humans. The mosquitos carry it for life, but are not affected otherwise.
The Dengue Virus (DENV) is part of the same genus as Yellow Fever, Japanese Encephalitis Tick Borne Encephalitis and the West Nile Virus. There are four closely related serotypes of the virus called DEN-1, DEN-2, DEN-3 and DEN-4. While infection from one serotype ensures the immunity from that particular serotype in the future, becoming infected with another serotype actually increases the chance of contracting severe dengue.
Signs and Symptoms
The key indicator that a patient has dengue is exposure to infected mosquitos and high fever. Dengue has a 4-10 day incubation period in humans and flu-like symptoms will start to appear after this time. WHO states that dengue should be suspected when a high fever of 40°C/ 104°F is accompanied by two of the following symptoms: pain behind the eyes, severe headache, muscle and joint pains, nausea and vomiting, rash or swollen glands. Dengue fever is often referred to as ‘break-bone’ fever as limb pain can be as agonising as actually having a broken bone.
Standard dengue symptoms normally last between 4-10 days. If after 3-7 days the patient is suffering additional symptoms such as severe abdominal pain, rapid breathing, persistent vomiting, bleeding gums, fatigue, blood in vomit or restlessness, severe dengue should be suspected. WHO states that the next 24-48 hours after suspicion of severe dengue are critical and proper medical care is required to prevent complications and potential death due to fluid accumulation, plasma leaking, respiratory disease, severe bleeding or organ impairment.
Dengue may be diagnosed clinically based on reported symptoms and a physical examination and/or blood testing. After the initial onset of dengue and for the next 4–5 days, the virus can be detected in serum, plasma, circulating blood cells and other tissues. As both malaria and dengue exist in similar environments and have similar symptoms, blood testing to rule out malaria may be also advised.
Where medication is prescribed for malaria, only supportive treatment is available for dengue. In severe dengue, maintaining the patient’s fluid volume is critical and requires medical intervention to administer intravenous fluid and potentially a blood transfusion. If severe dengue is suspected seek medical attention immediately.
Measures should be taken to eliminate the habitats of infected mosquitos, however the most effective form of personal prevention is to avoid getting bitten. Wearing light-coloured clothing that covers the skin, especially at dawn and dusk, using DEET based insect repellents as well as mosquito netting are standard preventive procedures.