Rising rodent numbers pose serious disease threat

Rising rodent numbers in Africa are raising the chance of an outbreak of diseases such bubonic plague, a conference in South Africa heard on Thursday.

The Rats and Human Health in Africa conference, attended by scientists and doctors from 20 countries, found rodent numbers in Africa are thriving as municipalities with growing populations struggle to manage sewage and refuse collection.

“[With] the increase in poverty and the rise in informal settlements the conditions are ideal for rodents to prosper and for the related diseases to flourish,” Dr Lucille Blumberg, of the National Institute for Communicable Disease in Johannesburg, told the conference.

A document drafted by the conference organiser, the United Kingdom-based Rodent Zoonosia Management (RatZooMan) project, says rodent-pest populations are worsening in Africa.

“Urban and peri-urban rodent populations generally increase with worsening sanitation and urban slums, which are growing in and around many African cities,” the document reads.

The RatZooMan project is funded by the European Commission and uses ecologists, epidemiologists, anthropologists and economists to monitor diseases in rats and humans.

Rodents are known to act as reservoirs for more than 60 different diseases, of which there are two categories. The first, which includes bubonic plague, are contagious and can be spread from human to human.

Bubonic plague is one of the most widespread of rodent diseases.
It comes from the bite of a flea and causes the lymph glands to swell. Some 2 421 people died of plague each year between 1987 and 2003.

About 90% of all bubonic-plague cases occur in Southern Africa.

Another contagious rodent-borne disease is Lassa Fever, which is prevalent in West Africa. Symptoms include vomiting, joint pain and headaches.

The second group is generally not contagious and is spread through rodent urine or faeces. These diseases can break out on a large scale in communities using common water and food sources that have become contaminated.

Two common diseases in the second category are leptospirosis and taxoplasmosis.

Leptospirosis penetrates the skin and mucous membranes and causes fever, diarrhoea and joint pain. Toxoplasmosis, also found in cats and birds, causes lesions and a build-up of fluid in the brain.

Research has found that toxoplasmosis cases are present in 25% of the world’s population. The seriousness of the sickness depends on the immune system of the infected person.

Most rodent diseases are spread by direct contact and by droppings in food. Some spread the disease to another host, such as a cat, which then passes it on to a human.

Dr Steven Belmain from the Natural Resources Institute in the United Kingdom says rodent-pest problems tend to be underestimated by the authorities, mainly because there is a lack of adequate information.

Many African countries, for example, have been reporting a growing proportion of cases of “fevers of unknown origin”.

“We simply don’t know enough about diseases such as leptospirosis, and it is quite likely that rodent diseases are misdiagnosed to be more common diseases such as malaria,” he says.

Belmain says scientists have found that deforestation and intensified agriculture are bringing people into contact with wild rodents, which carry different varieties of diseases. “What people are doing is fundamentally encouraging conditions for the spread of rodent-borne diseases,” Delmain says.

Research has found that changing weather patterns have attracted more rodents to areas with higher rainfall.

Professor Herwig Leirs of the University of Antwerp says rodent diseases are under-diagnosed and many go un-reported. This makes it difficult to know how prolific rodents diseases area. He says the world has not reached the point where it should panic about rodent diseases, but the risk of an outbreak is increasing all the time.

“Hygienic conditions are not what they should be, especially with the development of mega-cities,” he says. “Humans are also entering new habitats, which can put them at risk of contracting diseases from wild rodents. There has also been a development of resistance to treatments.

“Another important problem is that rodent diseases have more of an effect on people with immune problems, such as those with HIV.”

Scientists and doctors at the conference have found poor awareness among the general public and many health-care staff.

Awareness is complicated by the fact that some rodent diseases are similar to better-known diseases and by the difficulty in diagnosing the disease-causing agents such as bacteria, viruses and protozoa.

The HIV/Aids pandemic has intensified the problem of rodent diseases. People infected with HIV have weaker immune systems and are more susceptible to rodent diseases.

What can be done to solve the problem?

Leirs says when there are fewer rodents, fewer people will be infected with diseases.

“We need to do more to control the numbers of rodents.

“They breed very quickly. You will often find cases with the great-great-grandmother living with its great-great-grandchildren.”—Sapa

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