Yellow fever dengue Rift Valley Kyasanur forest disease Crimean Congo and Chikungunya

Apart from yellow fever, which will be covered in more detail below, a group of generally mild viral fevers including dengue, Rift Valley, Kyasanur forest disease (KFD) and Chikungunya, which at certain places and occasions take on a severe form resulting in vascular permeability, hypovo-laemia and abnormal blood clotting. Infection commences as an acute fever, malaise, headache, nausea or vomiting with petechial rashes, severe bruising, epistaxis and bleeding from various sites. After a few days, sudden circulatory failure and shock may occur producing a mortality of up to 40%.

Rift Valley Fever is normally a disease of cattle, sheep, camels and goats, in which high mortality can cause considerable economic loss, but spread to humans also occurs. A large number of unexplained abortions in livestock is often the first sign of an impending epidemic. The disease was normally restricted to Africa, but in 2000, it spread to Saudi Arabia and Yemen, raising the fear that it could infect other parts of Asia and Europe.

Some arbovirus infections can also be spread by non-mosquito arthropods, such as KFD and Crimea-Congo fever (see Section 16.9.2).

Control and prevention of arbovirus infections The main method of control is the destruction of vector mosquitoes and breeding places. The most important are Culex and Aedes mosquitoes, which live in collections of water close to the home. Search is made for larvae and all breeding places destroyed. A simple method is to use school children, making it a game or giving a reward for the number of breeding places found. Water tanks, blocked drains, discarded tin cans or old tyres are favourite breeding places. Large breeding areas (such as water tanks) can be covered, screened, treated with insecticides or natural predators introduced (e.g. fish or dragonfly larvae). An improvement on covering water pots and containers is to use an insecticide-treated pot cover rather than place the insecticide in the container.

Where there is an epidemic in a compact area such as a town, the quickest and simplest (although expensive) method of bringing the epidemic to an end is to use fogging or ULV aerial spraying. Compared with working hours lost, this can be a cost-effective procedure.

Personal prevention with repellents (see malaria) can protect the individual. The infected case should be nursed under a mosquito net so as not to infect other mosquitoes. A vaccine is available for Venezuelan, Eastern and Western equine encephalitis, which can be used both for humans and horses.

Where an animal reservoir is involved, some restriction of animals or reduction of rodents can help. In Rift Valley fever, special precautions should be taken in handling domestic animals and their products by wearing gloves and protective clothing. Blood and other body fluids of patients are also infectious, so barrier nursing should be instituted. All animals should be vaccinated. A vaccine for use in humans is under trial.

Treatment There is no specific treatment, supportive therapy being given (Ribavirin may be of value).

Surveillance Regular checks should be made on mosquito-breeding places and control methods instituted where mosquitoes are found. People can be taught to regularly search their home areas for mosquito breeding. (See further under yellow fever below.)

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