CholeraCholera is an intestinal infection caused by a bacteria - and is often linked to contaminated supplies of drinking water.
By the start of the 20th Century, six major cholera "pandemics" had affected countries across the world.
The world is now fighting the seventh, caused by a new strain of the Vibrio cholerae bacterium.
Epidemics involving this strain started in 1961 in Indonesia, spreading rapidly elsewhere in eastern Asia, and from there to India and Bangladesh, the USSR, Iran and Iraq.
The bacterium is part of the flora of brackish water and estuaries - it is when this water gets into the drinking supply that an outbreak can start.
It causes severe diarrhoea and vomiting, and patients, particularly children and the elderly, are vulnerable to dangerous dehydration as a result.
Treating the condition - or rather alleviating these severe effects, requires only simple measures.
However, the clean water and rehydration salts required are often in short supply in areas where they are needed most.
An outbreak of cholera can spread quickly in areas where there is poor sanitation and where water supplies can be tainted.
It is only rarely spread by person-to-person contact.
CarriersMost people infected with cholera don't actually get ill.
Despite this, they are contributing to the problem because the bacteria remain in their faeces for up to a fortnight.
Most symptomatic cases are hard to distinguish from other illnesses that cause diarrhoea - it is only in one in 10 that severe symptoms such as dehydration occur.
A well-organised response to cholera, says the World Health Organization, can reduce death rates to 1%.
An unprepared community, however, will experience many times this death rate, it says.
Normally, rehydration salts are the only treatment given, although severely dehydrated patients may need intravenous fluids.
Antibiotics can reduce the amount of diarrhoea.
VaccinesThere are two oral cholera vaccines - but these are mainly aimed at travellers rather than wider use in a community stricken by the illness.
Control of an epidemic is difficult in a community unless clean water supplies can be restored.
Systems for hygienic disposal of human wastes also need to be brought in.
Cooking practices need to be made as safe as possible - where practicable, food needs to be cooked thoroughly and eaten while hot, and raw fruit and vegetables avoided unless they are peeled first.
Handwashing after going to the toilet is a vital measure to prevent the spread of the disease.
MalariaMalaria kills over a million people a year and is second only to tuberculosis in its impact on world health.
The parasitic disease is present in 90 countries and infects one in 10 of the world's population - mainly people living in Africa, India, Brazil, Sri Lanka, Vietnam, Colombia and the Solomon Islands. There are four main types of malaria, all spread via moquitoes.
Ninety per cent of all malaria cases are in sub-Saharan Africa where it is the main cause of death and a major threat to child health. Worldwide, a child dies of malaria every 30 seconds. Pregnant women are also particularly vulnerable to the disease, which is curable if diagnosed early.
The economic impact of the disease is immense, causing many lost days of work and loss of tourism and investment.
What are the symptoms?Most people survive a bout of malaria after a 10-20 day illness, but it is important to spot the symptoms early. The first is high fever, followed a few hours later by chills. Two to four days later, this cycle is repeated.
The most serious forms of the disease can affect the kidneys and brain and can cause anaemia, coma and death.
Why has malaria increased?After years spent bringing the disease under control, the number of people dying from malaria is now higher than it was 30 years ago and has spread to new countries.
Although it is mainly a disease of tropical and sub-tropical countries, malaria has been identified in eastern European countries such as Russia and Turkey and recently a handful of cases were diagnosed in the US.
The increase in cases is due to a number of factors:
* the disease is becoming resistant to traditional treatments. In some areas of Asia, none of the major drugs is effective in fighting malaria.
* mosquitos are developing resistance to the main insecticides which have been used to control the spread of the disease.
* political and social upheaval has led to large numbers of people moving into new areas where disease is spread more easily.
* changes to the environment, caused by road-building, mining and irrigation projects, have created a good breeding ground for malaria.
* In many countries, budget restraints have led to malaria control programmes being cut back or abandoned.
How can malaria be contained?The amount spent on research into malaria was around $84 million in 1993. The main thrust of research is towards developing a cheap vaccine.
None has yet been developed which is proven to work for humans outside laboratory conditions. But scientists have discovered vaccines that work on a range of animals.
The spread of the disease can be reduced by cutting down the mosquito population, for example by filling ditches where mosquitos breed.
Early diagnosis can lead to successful treatment so education in spotting the symptoms of malaria is important. The spread of the disease can also be tracked and preparations made.
Bednets coated in insecticide have also reduced the incidence of the disease by up to 35%, according to the World Health Organisation.
Typhoid feverOver the centuries, the real killers in many wars haven't been the soldiers with their guns and bombs but a much more inconspicuous enemy - bacteria and other infectious micro-organisms. Typhoid is high on the list of culprits.
How do you catch it?These days, the main risk of typhoid for people in the UK isn't war but travel to an area where water supplies may be less clean than people in the UK are used to.
Typhoid is a major problem in the developing world, and is common in Africa and South America but the greatest risk seems to be in the Indian subcontinent.
There are nearly 150 cases of typhoid reported each year in England and Wales, with a similar number of cases of the related infection paratyphoid. But worldwide the figure is much more significant - 13-17 million cases with an estimated 600,000 deaths.
Salmonella typhiTyphoid fever is caused by the bacteria Salmonella typhi (S typhi). There are 107 different strains of this bacteria. Paratyphoid is caused by Salmonella enteritidis paratyphi A, B or C. It's usually a much milder infection than typhoid.
Symptoms include sudden onset of fever, severe headache, nausea, abdominal pain, loss of appetite, constipation or diarrhoea. These symptoms can be very severe and there is a one in ten mortality unless treatment is given. With antibiotics this can be reduced to one in 100, although resistance to antibiotic treatment is a growing problem. Multi-drug resistant strains of S typhi have been reported from Asia, the Middle East and Latin America.
Healthy typhoid carriersPeople who get typhoid carry the bacteria in their bloodstream and intestinal tract while they're ill. People can transmit the disease as long as the bacteria remain in their system. Most people are infectious just before and during the first week of convalescence.
About ten per cent of untreated patients will discharge bacteria for up to three months. A small number - about two to five per cent - will recover from typhoid but continue to carry the bacteria, shedding it in their faeces. These people are called carriers.
Main sourcesTyphoid is caught by eating food or drink that has been handled by someone shedding the bacteria, or if sewage contaminated with S typhi bacteria gets into the water you use for drinking or washing food. Polluted water is the most common source. This explains why typhoid is a worrying problem in disaster areas, where water supply and sewage disposal is disrupted and controls on food lost.
Vaccination against TyphoidVaccination is the other way to prevent the infection, and is recommended for any traveller to areas where typhoid is a problem (check with your travel agent when you book a holiday or arrange flights). But immunisation against typhoid is not a compulsory requirement for entry into any country. Neither is it routinely recommended for travel to industrialised countries.
A vaccine against typhoid was first developed more than a century ago in 1898. In recent years, new typhoid vaccines have been introduced that are more effective and much less likely to cause side effects. You can choose between a four-dose oral vaccine and a single dose injection. Both are up to 75 per cent effective in preventing the infection but there are important differences between them, not least the cost.
The NHS no longer routinely pays for travel vaccination, and you can expect to pay much more for the oral typhoid vaccine than the injection.
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http://news.bbc.co.uk/1/hi/health/medical_notes/120644.stm malaria
http://www.bbc.co.uk/health/conditions/typhoidfever1.shtml typhoid