Health & Fitness

Large dams pose malaria risk to millions in Africa

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Malaria is transmitted by the female Anopheles mosquito which needs slow-moving or stagnant water to breed. PHOTO | FILE

Summary

  • New findings published in the Malaria Journal reveal that over one million people in sub-Saharan Africa will contract malaria this year because they live near a large dam.
  • The study further reveals that construction of an expected 78 major dams in sub-Saharan Africa over the next few years will lead to an additional 56,000 malaria cases annually.
  • Dam reservoirs, particularly shallow puddles that often form along shorelines, provide a perfect environment for the malaria transmitting female Anopheles mosquito to multiply.

Kenya, like other sub-Saharan African countries, has built numerous dams to increase water supply for consumption, irrigation and electricity generation. Even though the dams have become integral to development initiatives in Africa, researchers now warn that they may increase disease transmission.

New findings published in the Malaria Journal reveal that over one million people in sub-Saharan Africa will contract malaria this year because they live near a large dam.

The study further reveals that construction of an expected 78 major dams in sub-Saharan Africa over the next few years will lead to an additional 56,000 malaria cases annually.

The researchers state that due to their link to malaria risk, new dam projects should be assessed accordingly for possible health impacts prior to their construction.

Malaria is transmitted by the female Anopheles mosquito which needs slow-moving or stagnant water to breed.

Dam reservoirs, particularly shallow puddles that often form along shorelines, provide a perfect environment for the insects to multiply.

“Dams are at the centre of much development planning in Africa. While they clearly bring many benefits contributing to economic growth, adverse malaria impacts need to be addressed or they will undermine the sustainability of Africa’s development,” said the study’s lead author, Solomon Kibret, a biologist at the University of New England in Australia.

El Nino rains

The study undertaken by the CGIAR Research Programme on Water, Land and Ecosystems looked at 1,268 dams in sub-Saharan Africa. Of these, just under two-thirds, or 723, were in malaria zones.

Kibret stated that the results show that the population around dams at risk of malaria is at least four times greater than previously estimated.

“Dams are an important option for governments anxious to develop,” says Matthew McCartney of the International Water Management Institute (IWMI) and a co-author of the paper.

“But it is unethical that people living close to them pay the price of that development through increased suffering and loss of life due to disease.”

As mosquito populations peak during rainy seasons when water levels rise in water bodies, the Health ministry will be monitoring these areas as the El Niño rains pound the country.

Aside from malaria, Dr Nicholas Muraguri, Kenya’s director of Medical Services, has warned that outbreaks of other water related diseases like Dengue and Rift Valley Fever could also increase.

“We are, therefore, stepping up efforts to create a state of preparedness in the health sector,” he said.

Those most vulnerable to malaria are those living in endemic zones found at the Coast and western Kenya, particularly around Lake Victoria.

Malaria epidemics are prevalent in highland areas of Kisii and parts of the Rift Valley, while North Eastern Kenya is prone to seasonal malaria outbreaks especially during rainy seasons. Dr Simon Kariuki, senior malaria scientist at Kemri, said that even though malaria cases have been reported in areas with dams, the disease transmission risk is still low compared to high risk malaria zones.

“But we should still take precautions to ensure that malaria control strategies in those areas are effective,” he said.

The study cites Kamburu Dam, located in eastern Kenya and used for electricity generation, as among those that have witnessed increased malaria cases.

The Nairobi Dam, which is now polluted and clogged with hyacinth, has in the past also been linked to the spread of malaria among communities living next to it.

Other dams in the country include Masinga, Gitaru, Kindaruma, Kiambere and Thika. Dr Kariuki noted that populations are still low in some dammed areas hence the low risk of malaria transmission.

“However, as population grows and people begin moving near these water bodies, their contact with mosquitoes will increase and enhance the spread of malaria.”

He added that a similar phenomenon occurred in parts of western Kenya where malaria prevalence was initially low. But as population rose and pressure for land increased, more people began cultivating near rivers where mosquitoes breed.

“This led to an increase in mosquito bites and more malaria cases,” he said.

Even with suitable breeding grounds, Dr Kariuki noted that for malaria transmission to occur temperatures need to be appropriate for mosquito breeding – usually about 27 degrees Celsius.

“If it’s too cold or too hot, breeding can’t take place,” he said.

But scientists warn that effects of climate change might raise temperatures in previously cooler areas thereby making them suitable for malaria transmission if they have dams. For mosquitoes to spread the disease, they first need to have “picked” the malaria parasite from an infected people while sucking their blood.

“Therefore, if there’s no reservoir of infected people where there’s a dam, then there will be no malaria transmission,” said Dr Kariuki.

Some of the malaria interventions that the Health ministry is scaling up during the current rainy season include bed net use, residual indoor sprays, prompt diagnosis and availability of effective drugs to treat patients.

To further reduce malaria risk in areas with dams, the study recommends that countries like Kenya can adopt operating schedules which at critical times, like during rainy seasons, dry out shoreline areas that offer breeding grounds for mosquitoes.

“Other environmental controls, such as introducing fish that eat mosquito larva in dam reservoirs, could also help reduce malaria cases in some instances,” the study says.

According to the 2014 Kenya Economic Survey, malaria claims about 23,000 lives every year, mainly children and pregnant women who are most vulnerable to the disease.

A 2013 study whose findings were published in the Malaria Journal revealed that malaria costs Kenya about Sh1 billion ($102 billion) annually, excluding costs associated with productivity loss in the event of death.

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