The first written evidence of such an epidemic occurred in the Yucatan in 1648. Since that time, much has been learned about the interesting transmission patterns of this devastating illness.



What causes yellow fever?

Yellow fever virus belongs to the Flaviviridae family, other members of which cause dengue fever and Japanese encephalitis.

The virus is introduced into the bloodstream via the saliva of the mosquito as it bites.

The virus can then be transported around the body and reproduce itself in a variety of the body's cells, usually the liver, kidneys and blood vessels. In serious cases, these cells may become damaged themselves.

What is the basic yellow fever transmission cycle?

There are two kinds of yellow fever, spread by two different cycles of infection.

Jungle yellow fever is mainly a disease of monkeys. It is spread from infected mosquitoes to monkeys in the tropical rain forest. People get jungle yellow fever when they are bitten by mosquitoes that have been infected after feeding on infected monkeys. Jungle yellow fever is rare and occurs mainly in persons who live or work in tropical rain forests.

Symptoms

The virus remains silent in the body during an incubation period of three to six days. There are then two disease phases. While some infections have no symptoms whatsoever, the first, "acute", phase is normally characterized by fever, muscle pain (with prominent backache), headache, shivers, loss of appetite, nausea and/or vomiting. Often, the high fever is paradoxically associated with a slow pulse. After three to four days most patients improve and their symptoms disappear.

However, 15% enter a "toxic phase" within 24 hours. Fever reappears and several body systems are affected. The patient rapidly develops jaundice and complains of abdominal pain with vomiting.

Yellow Fever Vaccinations:

The yellow fever vaccine is an attenuated, live-virus preparation of the 17D strain of yellow fever virus grown in leucosis-free chick embryos. A single dose correctly given confers immunity in 100% of recipients, and immunity persists for at least 10 years. Re-immunisation is currently recommended after 10 years.

This vaccination is given as a single injection given subcutaneously. If a country requires the vaccine for entry, travellers must allow at least 10 days before entering the country for vaccination.

Treatment of yellow fever:

Infection should be treated with appropriate antimicrobial therapy and tailored as antibiotic sensitivities are identified

Many cases of deep-seated infection or abscess require percutaneous or surgical drainage

Fever due to malignancy will usually regress with surgical debulking,

chemotherapy, and/or radiation directed at the primary tumor

Rheumatologic disorders may require NSAIDs, steroids, methotrexate, hydroxychloroquine, or other cytotoxic agents.