Fatal infection in an ailing nation

The conditions in Zimbabwe are perfect for the cholera outbreak there to claim thousands of lives.

An outbreak of cholera has claimed hundreds of lives in Zimbabwe, where a collapse of the health system and the lack of proper sanitation and sewerage has exacerbated the problem.

For the majority of us, diseases such as HIV and bird flu may seem like realistic dangers to our health, while cholera is something we often consider a disease of the past. But the recent cholera outbreak in Zimbabwe that has killed hundreds has come as a subtle reminder that there is still reason to fear this killer. During the 19th century, cholera spread repeatedly from its original source in the Ganges river delta in India to the rest of the world, before receding to South Asia. Six pandemics have been recorded, killing millions of people across Europe, Africa and the Americas. The seventh pandemic, which is still ongoing, started in 1961 in South Asia, reached Africa in 1971 and the Americas in 1991. The disease is now considered to be endemic in many countries and the pathogen causing cholera cannot currently be eliminated from the environment.

Cholera is an acute diarrhoeal infection caused by ingestion of the bacterium Vibrio cholerae, of which its O139 subgroup is responsible for the majority of outbreaks. In its most severe form, the condition is characterised by a sudden onset of symptoms that can lead to death from severe dehydration, shock and kidney failure. Cholera is so ravaging to the human digestive system because of the enterotoxin produced by its active bacteria that kills the cells responsible for regulating water flow into the intestines. Its extremely short incubation period - the time between when the body is exposed to a pathogen and when symptoms emerge - can sometimes be as short as two hours, enhancing the potentially explosive nature of outbreaks. However, about 75 per cent of people infected with cholera never develop any symptoms even though the bacteria can remain in their body for seven to 14 days and can spread into the environment, potentially infecting other individuals. Cholera is particularly virulent in individuals with weakened immune systems, such as malnourished children or people living with HIV.

But why are some people infected and others spared when they are exposed to the bacteria responsible the illness? Blood type has been found to a critical factor in susceptibility to cholera, as in malaria, where mosquitos seem to prefer certain types of blood over others. Research carried out at Massachusetts General Hospital suggests that an individual's susceptibility to cholera is heightened if they have type O blood, while those with type AB blood are the most resistant. Latin America is believed to have the highest proportion of people with type O blood in the world, which corresponds with its high frequency of cholera outbreaks. Individuals who carry a gene for cystic fibrosis also appear to be resistant to cholera.

But everyone can avoid cholera by having access to sanitised drinking water and efficient sewerage systems. The allowance and deliberate pumping or dumping of raw sewage into oceans and estuaries potentially facilitates cholera contamination of oysters and other shellfish, which can subsequently be transmitted to people who consume them. Currently, oral cholera vaccines do exist and in 2006 the World Health Organization (WHO) published official recommendations for their use in complex emergencies, but most treatments focus on rehydration therapy to replace the fluid and electrolytes lost. While antibiotics to fight the bacteria exist, some strains of cholera have become resistant to them.

Cholera's greatest tragedies emerge when sufferers cannot be treated because of a collapsed public health system. One dramatic example of this has been the cholera epidemic in Zimbabwe, a country ravaged by years of poor governance, with the Zimbabwean people paying the ultimate price. Once described as the breadbasket of southern Africa, exporting crops and meat to nearly all African countries and many other nations around the world, corruption and economic mismanagement have caused the healthcare system to collapse, limited the importation of medicines and medical supplies, and caused a mass exodus of healthcare professionals. Even a simple lack of spare parts to fix the country's water purification systems has made the nation vulnerable to outbreaks of cholera and other waterborne diseases, with many households having no water in their taps. Reservoirs and the underground water table have also been contaminated. But due to the nation's warm climate people require significant amounts of water every day and in their desperation have dug their own wells and collect water from streams and rivers. While collecting rainwater is one way of alleviating the problem during the rainy season, in times of drought and during the dry season, little or no water is available, elevating the population's risk for an outbreak of cholera.

The quadrupling of prices every 24 hours and the extremely harsh restrictions on the daily withdrawal allowance from banks has meant that most Zimbabweans cannot afford to buy bottled water or imported chlorine to purify their water. The stress of living in Zimbabwe and the constant fight to survive and to obtain even the most basic of commodities has resulted in many people becoming sick, reducing the life expectancy of its people to the lowest in the world for both men and women.

Nutritionally-deprived individuals are particularly susceptible to infections like cholera, and the lack of supplies such as saline drips that could help treat cholera sufferers means that a higher percentage of people who get cholera in Zimbabwe have died from the dehydration caused by the massive loss of water and salts. Cholera can spread with incredible speed if it is not addressed quickly. The world needs to act fast in order to limit the scope of this humanitarian disaster.

Dr Ross G Cooper is a senior lecturer in Human Anatomy and Physiology at Birmingham City University, England. Dr Usama Alalami is an associate professor in the department of Natural Science and Public Health at Zayed University.