Cholera

Cholera is an acute infection of the intestine which can be caused by two biotypes of bacteria: Vibrio cholerae and El Tor vibrio (now called Vibrio cholerae, biotype El Tor). The two biotypes sometimes co-exist. Cholera has no host other than man and is quickly transmitted, mainly through water and food, to persons with poor personal hygiene in areas where sanitation is deficient. The incubation period is short: from less than one day to five days. The disease is characterized by profuse painless diarrhoea and vomiting causing dehydration and acidosis. In all newly infected areas, adults of both sexes are usually affected, while in endemic situations cholera is mainly a paediatric problem. The vibrio is excreted in the faecal liquid and thus, in unsanitary conditions, easily spreads in infected water and foods (it is only rarely transmitted by direct person-to-person contact). In spite of the possibility of efficient treatment of cholera (which consists in rehydration by replacement of water, salts and alkali, supported in severe cases by antibiotic therapy, usually tetracycline) there is a problem of logistics, as cholera often occurs in areas where few treatment facilities are available. Excessive quarantine measures and restrictions on traffic and trade imposed in panic by different countries cause harassment, economic losses, and encourage the suppression of information which, in turn, favours the spread of the disease.

Cholera is one of the ancient diseases of humans which earned the notoriety of being a great killer during the nineteenth century when it reached Europe for the first time and caused six large pandemics. After the sixth pandemic, cholera retreated to its homeland in Asia, particularly in the deltas of the Ganges and Brahmaputra rivers, making occasional sorties such as the epidemic in Egypt in 1947. In 1961, El Tor vibrio moved out of its endemic sites, probably because of population movements in Asia and across the Pacific Ocean, to areas which had been free from cholera for many years and had few public health workers with experience in the diagnosis, treatment and control of the disease. The seventh pandemic thus began to spread from one country to another adjacent one in a predictable manner. It reached India in 1964, and almost replaced the classical V cholerae. The westward march continued until 1966, and after a temporary lull in 1967-68 the disease became widespread in some Mediterranean and neighbouring countries, and in 1970 invaded West Africa, a territory which had always remained practically free from the disease. In the wake of the westward extension of this seventh pandemic, a few European countries also experienced small outbreaks; others like Japan and Australia detected the importation of infection in time to prevent indigenous cases. Cholera returns in a seasonal pattern, and is often linked with the rainy season in a country. It is one of the diseases which could be exploited for biological warfare.

Countries or areas reporting major incidence of cholera to WHO as at July 1991 (number of cases; number of deaths) were: Africa: Angola (4,038; 56), Benin (1,086; 55), Cameroon (1,393; 172), Chad (7,550; 795), Ghana (6,493; 181), Mozambique (3,758; 91), Niger (1,229; 137), Nigeria (7,674; 990), Togo (682; 30), Zambia (11,356; 981), America: Brazil (18; 0), Chile (41; 2), Colombia (3,468; 65), Ecuador (24,435; 388), Mexico (27; 0), Peru (223,164; 2,163), Asia: India (319; 12), Indonesia (6,202; 55), Iraq (241; 1), Singapore (11; 0), giving a world total (including minor instances) of 303,504 cases and 6,174 deaths for just over half of 1991. 3,488 of these deaths were in Africa, with rates of death ranging from 6% to 10%, and as high as 30% in some areas.

The high rate of deaths from cholera is a reflection of the levels of poverty, mass migration and inadequate access to health care in some areas. In 1991, the death rate in Africa is far higher than that in South America, even though the number of reported cases is much lower; risk of death in Africa was worsened by factors including lack of access to life-saving oral rehydration salts, and delayed or incorrect management of cholera cases. WHO estimates that, with proper treatment, the death rate from cholera should not exceed 1%. In 1991, WHO reported that the El Tor cholera epidemic in Latin America has already claimed 1,500 lives. For the first time in several years, two cases of cholera occurred in Russia in 1993, with 17 reported in Russia as a whole. A new strain of cholera V cholerae non-01, called Bengal cholera, invaded Bengal in 1993, causing 107,297 cases of diarrhoea and 1473 deaths. Incidence of cholera is reported to be on the rise in the South Pacific region, possibly related to climate change.

Over 90% of cholera cases are mild and difficult to distinguish clinically from other types of acute diarrhoea, which kill an estimated 3.2 million children under the age of five each year. Although in newly-affected areas, many adults are among those struck by cholera, in the highly endemic areas, cholera is mainly a disease of children, whilst infants under one year of age being breast-fed are rarely affected.

In 1994, 61,960 cases of cholera resulting in 4,389 deaths were reported in Angola, the Democratic Republic of the Congo, Malawi, Mozambique and Tanzania (WHO 1995).

In 2002, an outbreak of severely dehydrating, watery diarrhea from the West Bengal province of India was been linked with the appearance of Vibrio cholera strains that are resistant to furazolidine, the drug of choice for cholera in developing countries.