Breaking down the spread of disease:
What does it take for a dangerous diagnosis to become the world’s next epidemic?
Twenty years ago, a new virus broke out in the small village of Kampung Sungai Nipah, Malaysia and killed over 100 people, mainly farmers. Aptly named, the Nipah virus has had recurring outbreaks each year since 1998, with the most recent outbreak this past May in Kerala, India, killing 17 of 19 infected. A July 16 report from the Center for Infectious Disease Research and Policy found that a 26-year-old index patient was responsible for infecting 17 of the patients in this outbreak. These patients included family members and hospital employees treating him. Over 3,000 individuals were tested and monitored throughout the outbreak, and the World Health Organization has urged more research to be done to prepare for future Nipah outbreaks.
In June, science news saw an uptick in discussion about the deadly virus, with many harboring concerns over the possibility of the “next Ebola.”
In June, science news saw an uptick in discussion about the deadly virus, with many harboring concerns over the possibility of the “next Ebola.” With fatality rates ranging from about 40 to 75 percent due to strain variability and limited availability of epidemiological surveillance or healthcare providers, these worries are understandable. But what does it take for this to become a serious global concern?
What is Nipah?
The Nipah virus is a zoonotic disease, meaning it is spread by an animal host. In this case, it’s spread by fruit bats of the Pteropus genus, a type of bat capable of living as far as Australia or Western Africa. These bats are only carriers of the disease, showing no symptoms themselves. However, through their urine and saliva on plants or fruit, the disease can be picked up by other animals like livestock, as well as humans. The Malaysian outbreak in 1998 spread to humans due to pigs that came in contact with these bats and served as intermediate hosts. Since then, humans have mainly been infected after eating fruit or sap contaminated by infected bats. From 2001 to 2008, half of the reported cases in Bangladesh arose due to human transmission between sick patients and their caretakers.
As for its presentation, Nipah may at first seem similar to other common sicknesses, like the flu. Initial symptoms include fever, headache, sore throat, aches, acute respiratory syndrome, and nausea, before leading to neurological issues, dizziness, and swelling of the brain (encephalitis). In the most severe cases, death is often caused by encephalitis and seizures that can end in a coma 48 hours after initial symptoms. But again, because these symptoms are not specific only to Nipah, it is difficult to detect an outbreak right away. Furthermore, the incubation period can last up to two weeks, making it more challenging to control for the spread for infection.
The more severe symptoms arise because Nipah targets both respiratory and nervous systems in humans, ultimately leading to inflammation of blood vessels and brain swelling. This is due to the virus attaching itself to ephrin-B2 and ephrin-B3 proteins which are found on the surface of nerve cells and blood and lymph vessels.
Tracking the spread of disease
Samuel Scarpino, Northeastern Assistant Professor in the Network Science Institute, focuses his research on building mathematical and computational models of disease transmission in order to better understand the dynamics of an outbreak. These models help to improve decisions in public health and preparations for future outbreaks of dangerous diseases.
It is much more difficult, and often controversial, to identify a pathogen before it spreads.
With colleagues such as Alessandro Vespignani, Scarpino and other Network Science Institute researchers work to generate a forecast after the disease has started spreading. It is much more difficult, and often controversial, to identify a pathogen before it spreads. “We’ve known about the Zika virus since the 1950s, but it was never on anyone’s radar,” Scarpino said. “Ebola has been around for nearly as long. But again nobody thought there was a big risk of an outbreak in West Africa, so trying to understand whether it is even possible to predict ahead of time which pathogens are going to cause outbreaks, where, and when — is a very active research area.”
While Scarpino has not done research specifically on the Nipah virus, two of his team’s main projects have revolved around the recent Ebola and Zika outbreaks.
“During the [Ebola] outbreak, one thing that we were actively working on was the role of poverty and the lack of healthcare infrastructure in West Africa in permitting the outbreak to become so large,” said Scarpino. “In these situations, the primary tool for stopping Ebola virus transmission is to isolate the exposed, care for the sick, and follow up with those in contact with the exposed or sick — so stopping the outbreak is directly tied to the healthcare infrastructure available.”
For Ebola, as Scarpino further explained, this was one of the main reasons it was so difficult to stop the outbreak. In some countries dealing with Ebola, especially Liberia, Sierra Leone, and Guinea, civil wars left them with no functioning health care system. On average, these countries had only nine hospital beds per 100,000 people before the outbreak. “Our calculations suggest that if the world had invested in their health care infrastructure ahead of time, the Ebola outbreak would have cost the global economy hundreds of millions of dollars less,” said Scarpino.
“Stopping the outbreak is directly tied to the healthcare infrastructure available.”
Issues like these are not uncommon and leave areas of the world in poverty traps. “We have situations where those individuals are sicker because they have less access to healthcare, less investment for infrastructure, and then that feeds back on those populations,” said Scarpino. “Populations that can’t emerge from poverty because they additionally have an increased health burden.”
Similarly, research funding faces socioeconomic biases based on disease geography. According to Scarpino, if Ebola had caused many infections in Western Europe, there would have been funding to quickly bring Ebola vaccines into late stage testing, which did not actually happen until the threat of Ebola leaving Africa.
The future of Nipah
What does all of this mean for the Nipah virus?
According to a 2009 study performed by the Center for Disease Control and Prevention, each person infected with the Nipah virus will only infect 0–1 other people. But for a disease to travel globally, each person must infect more than one person. This was the case for Ebola, where each infected person was likely to infect 1–3 other people during the 2014 outbreak throughout West Africa. Currently, this means that Nipah does not have the capability to spread much further than in the small annual outbreaks that occur. The recent update on the 2018 outbreak’s index patient may be an outlier, or it could be cause for more concern. After all, there was also no concern for Zika or Ebola to spread like they did.
“From my perspective, what’s interesting about it is that unlike Ebola, scientific and public health think they know one of the key animal reservoirs that can spread the disease,” said Scarpino. “With Ebola, we don’t understand the animal reservoir, making it much more difficult to control or prevent.”
Despite these statistics, Nipah virus remains a consistent concern for the World Health Organization (WHO) because Nipah is capable of sustained transmission from person to person, though it has not been able to spread very far. This is likely because, like Ebola, it is incredibly debilitating and immobilizes or kills infected patients very quickly.
“From a Nipah virus perspective, the current outbreak had more cases than some previously, but it doesn’t seem like there’s much risk if it’s not spreading beyond where it’s emerged,” said Scarpino. “But certainly a disease that fatal is a terrifying disease.”
Research, aid to healthcare infrastructures, and education around the disease can be steps in the right direction in hopes to prevent a pandemic.
The recent Nipah outbreak in India has news outlets and public health officials alike worried about the future of this virus. The EcoHealth Alliance, a nonprofit organization whose research aims to prevent pandemics, completed a flight pattern analysis to monitor the risk of an outbreak in other parts of the world; this was performed by studying flights from the five airports closest to the outbreak’s epicenter in order to see which cities would have the highest chances of being infected by a traveler. The WHO’s 2018 priority list of pathogens calls for an urgent need for research and development on the Nipah virus. For now, the Indian outbreak is under control and less than 20 patients have died. However, this does not mean that nothing needs to be done. Clearly, from a public health perspective, research, aid to healthcare infrastructures, and education around the disease can be steps in the right direction in hopes to prevent a pandemic.
Note from the author: If you are interested in Scarpino’s research, he is teaching a new class this fall called Networks and Biology. Throughout the semester, students will learn about the properties of diverse biological networks and gain skills in analyzing and performing statistical investigations of networked data, applying this knowledge to case studies like the spread of disease. To learn more, visit the course catalog (ENVR 2900) or email s.scarpino@northeastern.edu.
