More than half of emerging human infectious diseases—including SARS and Ebola—originate in animals
More than half of the new infectious diseases that plague humanity—including avian influenza, West Nile virus, SARS, and even Ebola—originated from animals. Now, new findings suggest that many of these outbreaks could have been detected earlier, and potentially prevented, had wildlife monitoring programs been in place.
Zoonotic diseases—those that jump from animals to humans—have become more common in the past 60 years. Biologists blame people, who have increasingly encroached on wildlife habitats. That’s provided more opportunities for diseases to jump from animals to people. Wildlife monitoring could provide advance warning of emerging diseases and give health authorities a chance to minimize the spread of an outbreak or better prepare for when a human outbreak does occur. Yet, few if any public health programs include wildlife surveillance.
In the new study, a team lead by Isabelle-Anne Bisson, a conservation biologist with the Smithsonian Conservation Biology Institute in Washington D.C., set out to assess whether information on wildlife health could be used to predict the emergence of disease in humans. The team looked at historical records of nearly 150 pathogens known to jump from wildlife to humans. They searched through 60 years of scientific and newspaper reports to determine two things: first, whether the pathogens cause visible disease symptoms or death in wildlife, and second, whether human outbreaks were preceded or accompanied by evidence of the disease in animals.
“These pathogens are invisible to the human eye,” Bisson says. “You can’t see them moving through a landscape, but you can certainly detect them through sick and dead animals.”
The team found that out of the nearly 150 pathogens studied, 75 caused visible symptoms in animals, such as seizures, lethargy, unprovoked aggression, or death, meaning signs of the disease could be easily detected. In reality, however, only 13 of the disease outbreaks in humans were preceded by reports in wildlife. This suggests that early warning signs for 64 of the zoonotic pathogens—45% of the total—may have been missed, the team reports online this month in EcoHealth.
“This study importantly shows the disconnect between tracking diseases in animals and in people,” writes Craig Stephen, a veterinary epidemiologist at the Canadian Wildlife Health Cooperative in Saskatoon who was not involved in the work, in an e-mail. “It [demonstrates] the need to respond to the signals found in nature and animal health.”
“Wildlife health is an important signal of environmental change, not just infectious disease, and is a very useful tool for predicting threats to human health,” adds Kathleen Alexander, a disease ecologist and wildlife veterinarian at the Virginia Polytechnic Institute and State University in Blacksburg, who was not involved in the study.
Ebola is a good example. Following previous outbreaks of the virus in northeastern Gabon and in the northwest of the Republic of the Congo in 2001, the Gabonese and Congolese ministries of forestry and environment, along with several wildlife organizations, implemented a temporary Animal Mortality Monitoring Network. Its purpose was to collect information from local hunters on their observations of dead primates and other mammals. Carcasses were then tested for presence of the virus. Wild animal outbreaks occurred before each of the five human Ebola outbreaks between 2001 and 2003, and twice, monitoring information was used to alert health authorities of an imminent risk of exposure weeks before a human outbreak occurred. Had a rapid response system been in place, experts say, the advance warning could have been used to implement actions to prevent the disease spread. (Whether a wildlife monitoring program could have minimized the extent of the current Ebola outbreak in West Africa is unknown.)
Although an ideal monitoring program would include the sampling of both healthy and sick wildlife by trained professionals, the researchers propose that less costly alternatives could be used to effectively collect information. The widespread use of mobile technologies such as cellphones could allow the public to participate in reporting suspicious wildlife deaths.
Since the team finished their analyses, at least two new zoonotic diseases have emerged—the H7N9 avian influenza strain and Middle East respiratory syndrome. “We really need to have surveillance systems in place,” Bisson says. “It’s a problem that’s going to get bigger and bigger.”