What Ebola could tell us about how diseases spread in NZ

What researchers discover about the spread of Ebola from bats in Africa could teach us more about how pathogens transfer from animals here in New Zealand. Photo / File

A Massey University specialist in deadly bat-borne virus Ebola has begun a major new study investigating how nasty pathogens jump from animals to us.

What Dr David Hayman discovers could help us better understand how many of the worst infectious diseases on the planet - Ebola, HIV/Aids and pandemic influenza among them - transfer from their animal hosts.

Called zoonoses, these can have devastating impacts on human health.

The most widespread epidemic of Ebola, which began in 2013, killed more than 11,000 people in West Africa and caused global panic before it was brought generally under control.

But predicting when, where, and why the animal-to-human transfer happens - what's called "spillover" - has so far proven elusive for researchers.

This was partly because such events were unseen and often not remembered, explained Hayman, who has spent years studying Ebola in West Africa.

"This can be because the first patient died, such as often happens in the case of Ebola virus outbreaks, but more often it's for less dramatic reasons.

"There is generally a lag between the time a person is infected and their illness, if indeed the first case is even ill."

In that time, most people would have moved and interacted with other people and animals.

Even for relatively common, domestic animal pathogens, such as many foodborne pathogens, it was often hard to know what the source was.

Massey University researcher Dr David Hayman. Photo / Supplied

"I generally work on wildlife as well and they are typically difficult to study.

"With notable exceptions, there is often little data on the animals themselves and even less on their infections."

Rather than focusing on how we treat infected individuals, Hayman wanted to understand when and why the jump to humans took place.

His new five-year research programme wil be broken into three key parts, each tackling a simple but critical question.

The first addressed how demography, such as birth and death rates of the host, affected when infections emerge.

Secondly, he aimed to determine how different types of infection - such as viruses, bacteria, or particular strains of either - changed the likelihood of an infection emerging.

Finally, he wanted to find how the physiology of the host, such as the use of flight in bats, determined the chances of spread.

"These are fundamental questions for infectious disease researchers working on emerging infectious disease, but also very applied questions when directed to emerging infections such as Ebola virus or endemic infections such as giardia."

To partly solve the questions, Hayman would build models that combined data from various infection sources to help him pinpoint differences in population infection dynamics.

Next, he would apply the model to specific cases in the US, Africa, and here in New Zealand.

"For part of the Ebola virus work, I will be working with colleagues who have access to the necessary high-containment labs in the US.

"We aim to culture the virus in cells to understand better how bat physiology impacts people once they are infected, but not the bats."

There was also field data being collected across the western US from hibernating bats to see why their physiology might make them more susceptible to a disease killing them, called white-nose syndrome.

Dr David Hayman has spent years studying deadly virus Ebola. Photo / 123RF

In another project at Uganda's Bwindi National Park, DNA and RNA would be extracted from the faeces of gorillas, cattle, goats and people.

This would allow his team to characterise the infections present in the difference species to understand how host relatedness, contact rates and pathogen type might affect emergence.

"And in New Zealand, we will be generating data on giardia parasites from people over time to understand how the presence of one specific 'type' might lead to the emergence of another".

Were there likely to be strong similarities in the way Ebola spread from bats in Africa and diseases spread from animals here?

"Possibly," Hayman said.

"Most infections of people from livestock and rodents in New Zealand will be through direct or indirect contact with infected faeces or urine, indirect usually being through water or contaminated food.

"We do not know how Ebola virus goes from bats, which we think are the reservoir hosts where the virus persists, to humans."

Because there was almost no evidence that the virus had been directly transmitted from bats to humans, it might be that there was an "intermediate host" infected, he said.

"For example, there is evidence for people getting infected from other primates, mainly when people in Central Africa have eaten dead apes, such as gorillas, that also die of the disease.

"But we do not know how the virus is transmitted from bats to apes, and one hypothesis is that apes are infected through eating contaminated food, as we think fruit-eating bats might be the reservoirs.

"But we don't know and there are no chimpanzees left in the region of West Africa the recent major outbreaks occurred in, so it may be possible that there has been more direct transmission."

Hayman's study is being supported with an $800,000 Rutherford Discovery Fellowship, administered by the Royal Society Te Aparangi.