Ebola virus disease (EVD), more commonly known as Ebola, is a severe and often deadly illness that affects humans and primates. Instances of the disease were at first limited to remote areas of Central Africa, but the most recent outbreak saw cases in urban West Africa as well. Spread and severity of an Ebola outbreak depend on the population of an affected region, the specific strain of the virus, and cultural aspects of human behavior. At the recent SIAM Conference on the Mathematics of Planet Earth (MPE16), held in Philadelphia, PA, Christina Edholm, (University of Nebraska) presented a model of Ebola that illustrates the importance of education in limiting future outbreaks.
Ebola spreads via direct contact with an infected patient's bodily fluids. Image credit: Wikimedia Commons.
Fruit bats, believed to be natural hosts of Ebola, initially transmit it by biting. It then spreads via direct contact with an infected patient’s bodily fluids, and has an incubation period ranging from two to 21 days. Unfortunately, because of the sometimes-lengthy incubation period, affected persons often do not initially realize that they are ill, and thus unknowingly spread Ebola via public transportation or familial contact.
At the disease’s onset, those affected typically only experience headache, fatigue, fever, or muscle soreness. But around the tenth or eleventh day of infection, patients develop a sudden high fever, and may begin vomiting blood or bleeding from the mouth, nose, and eyes. Excessive bruising, organ failure, and brain damage can also occur. Approximately 60 percent of cases result in death, and there is currently no vaccination.
Edholm studies cultural practices in West Africa to understand the role of education—or lack thereof—in Ebola transmission. When someone becomes sick, family members see it as their duty to care for the patient. Thus, an Ebola patient is more likely to stay at home or be treated by a community member who knows medicine rather than go to a hospital. As a result, the infected frequently infect their family members. Family members also commonly touch or kiss their deceased before burial, which is dangerous because Ebola can be transmitted even after the host has died. Healthcare settings are unfortunately often not much better-equipped, and patients are typically crammed in a small area with many exposed fluids.
After initially experiencing headache, fatigue, and/or muscle soreness, Ebola patients develop a high fever, internal bleeding, and the possible shutting down of organs. Image credit: Wikimedia Commons.
Edholm’s model analyzes the relevance of individual behavior, cultural behavior, and proper healthcare protocol in reducing or preventing future Ebola outbreaks. The model partitions the population of West Africa into two groups: those who take precautions against contracting the disease, and those who do not. She identifies “susceptible” and “educated-susceptible” as two variables representative of future patients. Once infected, a patient moves to subsequent classes (infected or educated-infected, respectively), then either hospital status, recovery, or death. Edholm stressed the importance of the gamma function, adding that varying alphas determine whether patients are in educated or uneducated environments.
After crafting the model—in collaboration with the Southern Africa Mathematical Sciences Association’s Masmau Program—Edholm conducted a parameter estimation using data from the 1976 and 1979 Ebola outbreaks in Sudan. She assumes that the population was uneducated in 1976 but educated by 1979. In 1976, 280 cases of Ebola were recorded in Sudan; only 38% of the cases originated in the community, meaning the remainder were spread in hospital settings. In 1979, only 34 cases were reported, 85% of which occurred in the community; the reduced number of cases indicates that the community was better prepared to handle an outbreak, and the low percentage of hospital cases suggests that healthcare staff was more sufficiently educated in preventative practice.
Thus far, Edholm’s parameter estimation is fitting the model well. “As healthcare starts moving towards early education efforts, and even preemptive education, we’re going to very much reduce the number of cases we’ll have overall,” she said.
|| Lina Sorg is the associate editor of SIAM News.