A lot of computing power and some serious modelling is needed to understand, and then predict, how far and how fast an epidemic will spread.
But as a sample exercise, go no further than the zombie apocalypse which has all the key components of a viral outbreak quickly spreading death across the country.
“Modeling zombies takes you through a lot of the techniques used to model real diseases, albeit in a fun context,” says Alex Alemi, a graduate student at Cornell University.
He and other researchers presented a model, The Statistical Mechanics of Zombies, to a meeting of the American Physical Society this year. The idea was to work out where the safest place was when the zombies started moving.
Zombies are the ideal carriers, from the point of view of a virus. They die but then keep moving, spreading the disease further. In most epidemics, the spread stops — or burns out — when the host dies. The sicker the infected person, the less risk of geographical spread.
Most fictional accounts assume all areas are affected at the same time but it is more likely that cities, with their large populations, would fall quickly. It would take months for zombies to arrive in the countryside.
“Given the dynamics of the disease, once the zombies invade more sparsely populated areas, the whole outbreak slows down — there are fewer humans to bite, so you start creating zombies at a slower rate,” says Alemi.
The best place to be in the zombie apocalypse is a remote area.
But the big real-life epidemic threat is Ebola. The latest outbreak in West Africa was the worst since the virus was discovered in the 1970s. Part of the reason is that it took a long time to diagnose or to be really sure that what was happening was the real thing.
If you are suffering from fever and unexplained bleeding you could be infected with the Ebola virus — but you probably won’t be.
The list of symptoms is long. The World Health Organisation (WHO) and Medecins sans Frontieres has them as fever, nausea with vomiting, diarrhea, fatigue, abdominal pain, loss of appetite, muscle pain, joint pain, headache, difficulty breathing, difficulty swallowing, hiccups and unexplained bleeding.
And one of the keys to controlling future outbreaks is being able to correctly diagnose Ebola.
Sometimes it’s not that easy. Adam Levine of the Rhode Island Hospital in the US says abdominal pain in combination with other Ebola-like symptoms actually turned out to be negatively predictive of Ebola.
“This may be because those patients actually had another disease like typhoid, which is more likely to cause abdominal pain,” he says.
He’s created an Ebola prediction score for better diagnosis.
One sure way to diagnose
But Ebola is so infectious that the biggest, most sure indication that someone has the deadly virus is they have been in contact with a suspected or confirmed Ebola patient.
Coming into contact with any body fluid will spread the disease.
Normally, an Ebola outbreak burns itself out quickly. The virus knocks victims down which means they don’t move too far and they don’t spread the virus.
However, the latest outbreak in Africa was severe and spread more quickly and further than usual because those infected stayed on their feet longer, infecting friends and family and anyone else they came in contact with — on the bus, at work, in a shop.
And the other reason was that the response to the West Africa outbreak was slow.
In March 2014, Guinea identified 49 cases of Ebola and reported these to international health agencies.
Nearly a year later, the epidemic has spread into neighboring countries, Sierra Leone and Liberia, and more than 22,000 had been infected with 10,000 already dead.
More deaths than all previous epidemics
This outbreak killed more people than all previous Ebola epidemics — 28,640 cases of the disease and 11,315 deaths.
The outbreak was studied by Mark Siedner from Harvard Medical School who found lessons for future public health emergencies.
The slow initial response revealed critical weaknesses. The national health systems in the Ebola-affected countries were ill-equipped, there were difficulties in engaging local communities and funding from international sources came late.
“The delayed response during the early stages of the epidemic in West Africa exemplifies not only the danger posed by disease outbreaks in states with weak health systems but also their widespread impact in an increasingly globalised world,” Siedner and colleagues wrote in the journal PLOS Medicine.
Had international agencies moved earlier after the first signs of an outbreak, it is likely that the number of lives lost would have been dramatically lower.
The local infrastructure played a big part — Guinea, Sierra Leone, and Liberia are all recovering from civil unrest and have health systems of limited capacity.
“When a disease of epidemic potential emerges, the international community should pay increased attention to the capacity of the local health system,” says Siedner’s study.
Overwhelmed and under-resourced, the affected countries used drastic measures to try to control the epidemic, including the closure of hospitals and schools, enforcing local and national quarantines as well as closing borders.
These actions brought widespread public distrust of health authorities.
Previous successful responses to other epidemics have prioritised early partnerships with local authorities, international experts and not for profit groups.
“In hindsight, some of the negative fallout from decisions to use extraordinary measures might have been avoided had WHO, in partnership with local community leaders and public health experts, more assertively used their legitimacy to caution against the use of coercive measures without an evidence base,” says Siedner’s study.
Although WHO declared a PHEIC (public health emergencies of international concern), six weeks passed until the US governmentâ€™s commitment of $US750 million and the planned deployment of 3,000 military personnel and 65 Public Health service staff.
In that time the cases of Ebola increased from 1,100 to more 6,500, and confirmed deaths more than tripled from 1,000 to 3,000.
The World Bank predicts that the three most affected countries will lose $US1.6 billion in economic growth in 2015, or about 12% of GDP across the three countries.
The difficulties, including the lack of resources and the scale of the problem, are highlighted by the experiences of Deborah Wilson, an American nurse who spent five weeks in an Ebola treatment unit in Liberia.
Infrastructure just wasn’t there
She says all pharmacy supplies had to be ordered from Europe. This included even the more common antibiotics, antimalarial tablets and drugs to treat nausea, seizures, pain, and fever.
A tent city grew around the two existing hospital buildings where Wilson worked. These housed medical and nursing staff, hygienists, water sanitation engineers and included areas for triage, a laboratory, a laundry, a pharmacy, a kitchen, a morgue and isolation sections.
Her job, and that of the hundreds of foreign volunteers and thousands of locals, was a daily challenge. She had to wear full protective clothing, including goggles to keep eyes safe from spilled bodily fluid, work in the tropical heat as well as wear gloves at all times.
“Patients couldn’t see the faces of those caring for them, and this was particularly distressing for children, many of whom were in the isolation area alone because their family members either had died or were infected,” she writes in the American Journal of Nursing. “Patients could be touched only with gloved hands, and this profoundly limited nursesâ€™ ability to establish human connections.”
Some patients survived only to face problems when they returned home.
“It was always clear from their faces that they had been through a lot and needed time to heal further,” Wilson says.
“They were in a weakened state, and some were the sole survivors in their families. It was hard for us to fathom what their future would be like, but in those first moments of freedom, they were cheered and applauded by the ETU (Ebola Treatment Unit) teams.”
Each recovered patient received a mosquito net and a two-week supply of therapeutic supplements for malnutrition. Many of those infected with Ebola also tested positive for malaria.
Survivors often faced rejection from others, grief over the loss of loved ones and hardships from loss of income, possessions, and even homes. Many houses of the infected were burned as locals tried to contain the virus.
“When we learned that recovered patients who returned to their villages were being rejected and forced to live on the outskirts, we began issuing them certificates of discharge,” she says.
The medical staff also started hugging the recovered patients in public, letting everyone know there was no risk of infection.
And some came back. Survivors were sometimes recruited to work in the Ebola Treatment Unit as caregivers for ill and orphaned children.
Liberia is due to be declared free of Ebola transmission on January 15.