There is also the fragile balance which must be maintained between the risk of the disease and the risk of the drugs. There are a number of toxic effects with all these drugs, such as nausea, vomiting, severe gastrointestinal disturbances, and even psychotic reactions. Chloroquine can cause bone marrow suppression, heart problems, a neuropsychiatric syndrome and brain dysfunction. The British Compendium of Data Sheets 1996-7 also lists skin eruptions, itching, hair loss and skin depigmentation. Prolonged high doses of chloroquine can lead to damage to the retina of the eyes, ringing of the ears or convulsions. One doctor reported that his 6 year old son had a grand mal seizure after taking the drug (BMJ, 1996; 312: 1421).
Other sulphur drugs such as sulphadoxine purimethamine are effective but also cause rapid development of resistant strains (The Lancet, 1996; 347: 244-8).
The natural compound quinine, made from cinchona bark, remains more than 85 per cent effective nearly everywhere and has been a mainstay of malaria treatment for three centuries. Nevertheless, it is starting to lose its effectiveness in Southeast Asia.
It also can be toxic, causing dysphoria, tinnitus and high tone deafness, hypoglycemia and even serious cardiovascular or nervous system effects (New Eng J Med, 1996; 335: 69-75 and 800-6).
As drug resistance grew, so tropical disease experts turned to mefloquine, marketed as Lariam by Swiss pharmaceutical giant Hoffman-La Roche. Besides its effectiveness, this once a week anti malarial quickly became popular because of its convenience (The Lancet, 1996; 348: 344). However, because it tends to stay in the system for a long time, the potential for adverse reactions also appears heightened (see box below). And now holfantrine is being looked at as a possible new drug, although there is evidence of toxicity of the heart (Lancet, 1993; 341-1044-49).
Another problem is the potential for drug interactions between the drugs, particularly as more than one are often taken (New Eng J Med, 1996; 335: 800-6).
Many hopes had been pinned on trials of SPf66, a new vaccine developed by a team in Colombia. After a series of studies, protectiveness was found to be only 31 per cent, but was nevertheless considered encouraging (The Lancet, 1994; 344: 1172-3). However, a later randomized double blind trial study of infants in the Gambia showed that the vaccine was useless, as did a study of children in northwestern Thailand (Lancet, 1995; 346: 462-7 and 1996; 348: 701-7).
Thechances of getting malaria varies a great deal from area to area, and it also depends on when and how you travel.
Travellers to Africa are at risk in most rural and many urban areas, particularly during the evening. Most travellers to Asia and South America, however, spend most of their time in towns or resorts where there is limited, if any, risk of exposure, and they travel to rural areas mainly during daylight hours when there is also limited risk of infection.
Cholera (Vibrio cholerae) infection is caught from contaminated food or water and usually results from poor sanitation. In a 1991 epidemic in Peru of over 16,400 cases and 71 deaths, the epidemic was traced to drinking unboiled water, or water from a household water storage container (Lancet, 1992; 340: 28-33).
Cholera vaccination is no longer recommended for the current outbreak in South and Central America. There have been some instances in African countries where a vaccination certificate has been requested at the border, but this is not common. In any case, cholera doesn't appear to pose a serious threat to Britons, since only about 30 contract it every year, according to the Public Health Laboratory Service. Risks are higher in America, with its proximity to South America, where 10 cases were reported in only three states, following the big epidemics in South and Central America in the early 1990s (JAMA, 1991; 265: 2658-9).