Yellow Fever

Earlier this year, Angola was faced with a yellow fever outbreak, which has infected and killed hundreds of individuals. This is the first epidemic of the disease to hit the country in 30 years. Yellow fever is a mosquito borne illness that is spread by mosquitoes of the Aedes species. This further highlights the importance of these emerging and reemerging diseases that pubic health must confront.{{more}}

Yellow fever occurs in 47 endemic countries in Africa, in Central and South America. Around 90 per cent of cases reported every year occur in Sub-Saharan Africa. Infected travellers from areas where yellow fever occurs can export cases to countries that are free of yellow fever, but the disease can only spread easily if that country has the mosquito species able to transmit it, specific climatic conditions and the animal reservoir needed to maintain it.

The yellow fever virus is transmitted by infected mosquitoes, most commonly from the Aedes species – the same mosquito that spreads the Zika, Chikungunya and Dengue virus. Haemogogus mosquitoes also spread yellow fever and are mostly found in the jungle. Mosquitoes become infected with the virus when they bite an infected human or monkey. The disease cannot be spread by contact from one person to another.

Mosquitoes breed in tropical rainforests, humid, and semi-humid environments, as well as around bodies of still water in and close to human habitations in urban settings. Increased contact between humans and infected mosquitoes, particularly in urban areas where people have not been vaccinated for yellow fever, can create epidemics. Outbreaks of the disease are of particular concern when they occur in overcrowded settings with inadequate water supply and waste management services that allow the mosquitoes to breed easily.

Once contracted, the yellow fever virus incubates in the body for three to six days. Symptoms usually present themselves in two phases. The first, “acute” phase usually causes fever, muscle pain with prominent backache, headache, shivers, loss of appetite, and nausea or vomiting. Most patients improve and their symptoms disappear after three to four days. However, a small percentage of people enter a second, more toxic phase within 24 hours of the initial remission. They will experience high fever, jaundice, and abdominal pain with vomiting and deteriorating kidney function. Bleeding can occur from the mouth, nose, eyes or stomach, with blood appearing in vomit and faeces. Half of the patients who enter the toxic phase die within 10 to 14 days; the rest recover without significant organ damage.

There is no specific treatment for yellow fever, but good supportive treatment of symptoms, such as dehydration, fever and infection, improves survival rates. Yellow fever can be prevented by an extremely effective vaccine that is protective for life.

Vaccine is the most important means of combating yellow fever. The yellow fever vaccine is safe and affordable, and a single dose provides lifelong

immunity against the disease. To prevent outbreaks in affected regions, vaccination coverage must reach at least 80 per cent of the population at risk.

Mosquito control can also help to prevent yellow fever, and is vital in situations where vaccination coverage is low or the vaccine is not immediately available. Mosquito control includes eliminating sites where mosquitoes can breed and killing adult mosquitoes and larvae by using insecticides in areas with high mosquito density. Community involvement, through activities such as cleaning household drains and covering water containers where mosquitoes can breed, is a very important and effective way to control mosquitoes.

Dr Rosmond Adams is a medical doctor and a public health specialist.

He may be emailed at adamsrosmond@gmail.com