Infectious disease

Mosquitoes allow the spread of malaria, which kills millions

Malaria

Malaria is a public health problem in some 90 countries, and causes between 1.5 and 2.7 million deaths world-wide each year.

A malarial mosquito passes on the disease by sucking the blood of humans

It is caused by a parasite called a Plasmodium, which is passed on from infected humans when they are bitten by mosquitoes, which then go on to bite non-infected people.

The symptoms are bouts of fever, tiredness, headache, nausea, and muscular pain, leading, without treatment, to delirium, convulsions and death.

If treated promptly, it is a curable disease, and travellers are advised to take a course of anti-malaria drugs to protect them before going abroad.

However, nothing can provide 100% protection against malarial infection.

AIDS

AIDS, or Acquired Immune Deficiency Syndrome, is linked to HIV virus, which can be passed from human to human through blood to blood contact.

Although HIV is symptomless, over time, it reduces the body's ability to deal with outside infections.

When the body's immune system has been rendered ineffective, it is highly vulnerable to other predatory infections, such as TB, which may have already been lying dormant.

Although once full-blown AIDS has developed, it becomes increasingly difficult to treat these infections, the HIV-positive stage can be lengthened by many years using modern anti-viral treatments.

AIDS is commonly spread by unprotected sexual intercourse, both homosexual and heterosexual, and is a major killer in developing countries, where there is a higher degree of infection in the heterosexual community, and less use of protection such as condoms.

In these countries, immune resistance is generally lower due to poorer nutrition and general health, and consequently, the development of full-blown AIDS, and death from opportunistic infections is far swifter.

Tuberculosis

Tuberculosis is a lung disease caused by infection with a bacteria.

Poor living conditions make people vulnerable to disease

Its symptoms are a persistent cough, which may involve coughing up blood, fevers, night-sweats, weight loss and tiredness.

Although it kills many people world-wide, particularly children, it is rare in the UK, with many of the 5-6,000 annual reported cases coming from people recently returned from trips abroad.

Once contracted, it can lie dormant in the lung, only developing into the disease if the body's immune system weakens.

Treatment is by a six-month course of antibiotics, and provided this is followed, the cure rate is high.

However, symptoms generally disappear long before the end of the treatment course, and the failure of many people to continue for the full six months has been blamed for the emergence of TB strains resistant to antibiotics.

Many children, including British teenagers, are inoculated against the disease with the "BCG" vaccination.

Measles

Measles was prevalent among children in the UK until recent years - the last mini-epidemic was in the late 1980s.

But the disease, characterised by the purple-spotted skin rash and high temperatures, can cause permanent disability or even kill.

Vaccination can prevent measles and tuberculosis

And in developing countries, where poorer nutrition and living conditions have reduced children's natural immune response to the virus infection, it is fatal far more often.

In this country, the MMR (Measles, mumps and rubella) vaccination is given at around 14 months of age, and has virtually eradicated the disease.

However, recent scares linking the vaccine to autism and bowel disease have reduced the uptake of the jab, and UK public health experts have warned that another epidemic is possible.

Diarrhoeal Diseases

Clean water prevents outbreaks of diarrhoeic disease

Poor hygiene and water supplies are the main factors behind the spread of diseases like dysentery and cholera.

Both, although quite treatable, cause death through dehydration, as the body cannot replace the water and body salts it loses through diarrhoea attacks.

All are far more prevalent in developing countries, which may have no efficient sewage disposal system, leading to the contamination of water supplies.

More recently, the breakdown of proper water treatment facilities in eastern European countries such as Latvia has led to outbreaks of diseases like cholera.

In the UK, the past decade has seen a vast increase in the number of food poisoning cases reported to the authorities.

Again, these are rarely fatal, although the potent 0157 strain of the E.coli bacterium killed many elderly or sick patients during a recent Scottish outbreak.

Acute respiratory infections

Pneumonia is a term used to refer to a variety of lung infections caused by viruses, bacteria and parasites.

Common symptoms include fever, a cough, rapid breathing, chest pain, and perhaps a bluish or grey colour of the lips or fingertips, indicating that the body is not getting enough oxygen through the lungs.

One of the most dangerous forms is Pertussis, or Whooping Cough, which is prevented in many parts of the world by a vaccination.

Once an infection has taken hold, a principal treatment, either given to tackle the bacterial infection itself or act prophylactically.

Young children in developing countries, many immuno-suppressed and suffering from other infections, find it extremely difficult to fight off the disease.

Many respiratory tract infections are very infectious, particularly in the early stages, and can be spread through droplets from sneezes or coughs, or from dirty tissues or water glasses.