afrol News, 17 November - The next Ebola outbreak should be expected to occur "in northern Congo Brazzaville, towards Cameroon and the Central African Republic," according to African scientists that have closely studied the pattern of the deadly disease. They found that Ebola affect many Central African mammals besides humans and that the disease fluctuates with climate variables throughout the Gabon-Congo region, making predictions possible.
Sally Lahm has led a decade-long research into the roots and patterns of Ebola outbreaks in Gabon and Congo Brazzaville. Working as a research associate at the Institute for Research in Tropical Ecology in Makokou, Gabon since 1982, she was originally conducting unrelated ecological studies. But the outbreaks of Ebola virus in humans prompted her to explore how the disease was affecting animal populations in the region.
Between 1994 and 2003, she and her team collected reports of animal illness and deaths from wildlife survey teams, villagers, hunters, fishers, loggers, miners, Ebola survivors and families of victims from across Gabon and into north-western Congo Brazzaville.
Despite the low probability of finding dead animals in the humid forests that cover most of the region, due to the scavenging by animals and insects and rapid decomposition, Ms Lahm received and verified reports of 397 dead animals. The carcasses, which were found at 35 different sites in Gabon and Congo, included gorillas, chimpanzees, mandrills, bush pigs, porcupines and four species of antelope. Tests from 12 out of 35 sites proved sick or dying animals with Ebola symptoms. In addition, 16 reported wildlife mortality incidents coincided with known Ebola epidemics.
This had shown that "the transmission of Ebola within animal populations is much more widespread than previously believed," explained Ms Lahm. "Ebola appears to spread both within species and between different species of animals."
To determine the extent of human exposure to Ebola within Gabon, Ms Lahm collaborated with Maryvonne Kombila of the University of Health Sciences in Libreville, Gabon, and with Robert Swanepoel of the National Institute of Communicable Diseases in Sandringham, South Africa. Mr Swanepoel tested for antibodies to the Ebola virus in more than one-thousand human blood samples that had been collected by Ms Kombila and her colleagues for other research in Gabon between 1981 and 1997.
Fourteen of the blood samples tested positive for antibodies to Ebola. Some people had been exposed at least three years before the first known Ebola outbreak in Gabon, while others lived in regions where no known epidemics had occurred.
In 2003, Ms Lahm was able to track down six of the people whose blood samples indicated that they had been exposed to the Ebola virus. Life history interviews revealed that some of the antibody-positive people had never visited a region where known Ebola outbreaks occurred in humans. "Therefore people have been exposed to the Ebola virus where it has not been recognised," the African scientist team concludes.
Based on their findings, the researchers were able to identify relationships among previously documented Ebola outbreaks in humans and wildlife in Gabon and Congo Brazzaville that initially seemed disparate and unrelated. They proposed that the virus first spread southwest across Gabon. It then looped back toward the northeast from sites in western or central Gabon and caused the most recent outbreaks in Congo Brazzaville.
"If the spread of the Ebola virus follows its current north-eastward path, the next outbreak would be expected to occur in northern Congo Brazzaville towards Cameroon and the Central African Republic," predicted Ms Lahm after assessing the team's findings.
However, according to the same findings, the spread of Ebola also depends on climate factors. Illness and deaths among animals were most prevalent during periods of prolonged drought-like conditions in the rainforest, which had indicated that "severe environmental stress may facilitate disease transmission," according to the team.
In the study, the researchers urge that "public education is needed" to decrease human contact with potentially infected wildlife by discouraging people from scavenging dead animals and by promoting safe hunting and trapping practices, especially because the results show that outbreaks in wildlife populations have been much more frequent than previously believed. Ms Lahm's team therefore does not go as far as non-African scientists, which have called for a total ban on bushmeat.
They further emphasise that "monitoring wildlife in collaboration with rural African residents" could provide information essential for protecting public health as well as comprehending the ecology of the disease. Gabonese and Congolese forest resident - which the team spent much time together with during the last decade - could be the most competent in detecting an Ebola outbreak among forest mammals, thus alarming scientists before it spreads to the human population.
Ms Lahm points out that there remain many unanswered questions about Ebola including how the virus spreads within and between mammal species. "Our study provides more pieces of the puzzle, but at the same time it is enlarging the puzzle," she modestly concludes.
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