Dysentery drug shows early promise

Behind the Headlines

Monday May 21 2012

New drugs are needed to help fight amoebic dysentery

A cheap drug already prescribed for arthritis “could fight amoebic dysentery”, reported the BBC.

Amoebic dysentery is a parasitic infection that causes diarrhoea containing blood or mucus. Although rare in the UK, it is widespread in the developing world and can be a major health risk to both travellers and locals. If left untreated it can lead to serious complications and even death. It is usually treated with certain antimicrobial drugs, but there have been some concerns about the potential for amoeba becoming resistant.

The condition has been in the headlines as scientists have developed a new way to rapidly test a wide range of chemicals and drugs in the laboratory in a bid to find potential new treatments. During the early stages of research, scientists tested 910 different candidates and found that a drug approved in the US for the treatment of rheumatoid arthritis showed the greatest promise for the treatment of amoebic dysentery.

As yet, this drug has only been tested on amoebas grown in the lab and on small numbers of mice and hamsters. Human testing will be needed to determine if this drug is useful for the treatment of amoebic dysentery in humans. The best way to fight amoebic dysentery is to avoid potential infections when abroad, through precautions such as practising good hand hygiene and avoiding unclean water.


What is dysentery?

Dysentery is an infection of the intestines that causes diarrhoea containing blood or mucus. It is mainly caused by an infection from either bacteria or amoebas. Amoebas are a type of tiny, single-celled organism. The parasitic amoeba that causes dysentery is called Entamoeba histolytica, which is found mainly in tropical areas. Amoebic dysentery is rare in the UK, and when it does occur, it is most likely to have been picked up abroad. However, dysentery can also be caused by bacteria called Shigella – this type of dysentery is more common in the UK than amoebic dysentery. Amoebic dysentery is more serious than dysentery caused by bacteria, although both forms can be fatal if not treated.


How can someone catch amoebic dysentery?

Amoebic dysentery is caught when a person ingests faecal material containing the Entamoeba histolytica organism, often through drinking unclean water. Amoebic dysentery (also called amoebiasis) is more common in countries with poor sanitation, particularly tropical areas such as parts of Africa, South America and India. Amoebic dysentery is reported to result in about 70,000 deaths worldwide each year, and many more non-fatal infections.

To reduce the chances of catching the bug, it’s important to use good hand, food and water hygiene, particularly when travelling in areas where the disease is common. It’s also important to avoid drinking unclean or suspect water that may carry faeces or infectious micro organisms, and stick to sources such as sealed bottles of clean water. Avoid products such as ice cubes and salads, which may have been prepared with dirty water.


How is amoebic dysentery currently treated?

People with amoebic dysentery are usually treated with an antibiotic called metronidazole. However, there are side effects associated with this drug. There are also concerns that Entamoeba histolytica may become resistant to metronidazole. Given these and other concerns about the over-use of antibiotics, there is a need to develop new ways to treat amoebic dysentery.


What did the research look at?

Rather than testing a specific drug in patients, the research covered in today’s news initially aimed to develop and test a way to screen a large number of existing drugs chemicals in the laboratory to identify any that might be effective against Entamoeba histolytica. Any promising drugs could then be prioritised for further study. After identifying a potentially useful drug, researchers went on to test its effects in two animal models of amoebic dysentery.

The researchers were able to develop a method for rapidly testing a large number of chemicals in the laboratory for their effect on Entamoeba histolytica. They used their method to test 910 different chemical compounds in total, and found that 11 of these compounds reduced the growth of Entamoeba histolytica. The most effective compound was a drug called auranofin, which was 10 times more effective at killing the amoeba in the laboratory than the same concentration of metronidazole, the conventional treatment for amoebic dysentery.

Auranofin is a drug that contains gold, and it was approved in 1985 by the US Food and Drug Administration (FDA) for the treatment of rheumatoid arthritis. People with rheumatoid arthritis take it orally.

Auranofin was then tested in mice whose intestines had been surgically infected with Entamoeba histolytica. Auranofin was found to reduce the number of Entamoeba parasites in the intestine, and the level of inflammation in the intestine, while metronidazole did not. Auranofin also reduced amoebic liver damage in hamsters infected with Entamoeba histolytica.


What did the researchers conclude?

The researchers concluded that their method was able to identify drugs that might be effective against amoebic dysentery, and that auranofin is a promising potential treatment for the condition.


What does this mean for the treatment of amoebic dysentery?

As yet, research into the effect of auranofin on amoebic dysentery is at an early stage. As it already has approval in the US for another condition (rheumatoid arthritis), this may help the drug to reach human testing stages for amoebic dysentery more quickly. However, tests in people with amoebic dysentery will be needed to determine whether this drug is effective and safe for this condition.

Currently, the drug does not appear to be licensed by the European Medicines Agency for the treatment of rheumatoid arthritis or other conditions.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Cheap amoebic dysentery drug 'promising'. BBC News, May 20 2012

Links to the science

Debnath A, Parsonage D, Andrade RM et al. A high-throughput drug screen for Entamoeba histolytica identifies a new lead and target. May 20 2012


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