Call of the wild: the future threat of animal diseases

When it comes to infections that start off in animals, it is a case of better the devil you know than the devil you don’t. According to the experts, the worrying ones are those that have not yet been identified.

Most infections that have not been identified - referred to as new and emerging infections - start off in animals. That was true with HIV, it was true with vCJD, the human form of mad cow disease, it was probably true with SARS, and it was certainly true recently with avian and swine flu.

Infections acquired from animals, called zoonoses, can be caught through direct contact or via food and water.

Some animal diseases can be caught by humans but transmission stops there. Brucellosis, for example, is endemic in Africa, the Middle East, central and south east Asia, South America and some Mediterranean countries, and most commonly affects sheep, goats, cattle and pigs.

Also known as undulant fever or Mediterranean fever, it is caused by the bacterium Brucella. Humans from time to time will get infected, but they do not then pass it on to other people, so it cannot cause an epidemic. For the infected individual, however, it can be a nasty experience.

Diseases tend to adapt to their host, so in a different host they can actually be more severe than they were in the ordinary host, explains Chris Whitty, professor of international health at the London School of Hygiene and Tropical Medicine and past chair of the national expert panel on new and emerging infections.

“One of the reasons many infections start off extremely unpleasantly when they first jump the species barrier is because of this.”

The more worrying ones are those that involve viruses that jump the species barrier and can then be transmitted from human to human, partly because many more viruses exist but also because viruses have the ability to mutate rapidly.

Professor Whitty says: “That’s what happened with HIV and flu and it does from time to time with pandemics. Taking flu specifically, almost every flu pandemic starts when animal flu jumps the species barrier.”

He explains that swine flu has become a pandemic because of the nature of the specific virus that causes it.

There are a lot of different types of flu viruses and they vary in terms of how good they are at being transmitted from person to person. With avian flu, H5N1, it appears that it has not been possible to transmit it from person to person. But swine flu, H1N1, is transmitted from person to person and as a result it spreads very quickly.

But Professor Whitty points out: “Avian flu kills a lot more people who actually catch it, so although it’s a very small number, those people who get it have a very substantially increased risk of dying, even if they’re young adults.

“Swine flu is not a trivial disease and will kill a lot of people, probably, but it’s nowhere near, per case, as virulent as avian flu.”

Factory farming

Occasionally zoonoses originate in the UK - vCJD, for example, arose because brain matter was fed to animals.

UK Public Health Association chief executive Angela Mawle points the finger at factory farming.

“If you look at industrial farming, it’s not just the condition of the animals that causes concern, it’s the kind of conditions it creates for viral mutations, of the transition between species,” she says. “And therefore by animals living in conditions which immune suppress them, there’s a real optimum chance of new viruses developing rapidly.”

These animals with immune suppressed systems act as “incubators” for viruses and then transmit them, she adds. While not opposed to cheap food production, which is essential for tackling health inequalities, she believes it is a false economy if viruses are made at the same time. The solution is not to ban factory farming, but to push for better hygiene and less overcrowding.

But most zoonotic infections do not arise from factory farming, argues Professor Whitty. Equally, he believes global warming, overall, is not a driver of new infections. So what is?

“The main effect is to do with movement of populations and animals that may bring people together in ways that haven’t historically happened,” he says. “People travel a lot more so the speed of spread of things can be much more than it would have been, let’s say, a couple of hundred years ago.”

Viruses have always jumped the species barrier but today there is greater awareness of them because of international travel and also because of intense media coverage.

Professor Whitty says: “Media reactions to new infections are usually very extreme and lead to panic, which may be justified but generally isn’t. If you think about the SARS epidemic, for example, SARS was a new infection, a very unpleasant infection. Eventually it killed fewer than 1,000 people but it had huge impact on the economies of south east Asia, and that was because people were so concerned about it.”

Part of the reaction is about uncertainty, and when people become more certain about an infection they tend to respond in a more measured way because they understand the risk. The H1N1 swine flu pandemic is an example of that. When it first came out there was a huge amount of media attention, but as it became more understood the attention died down and a more measured approach was taken.

Another infection that initially generated an immense amount of media attention and anxiety among the public is bovine spongiform encephalopathy - BSE. Not all the lessons from the Phillips report into the BSE crisis have necessarily been learned, says Dilys Morgan, chair of the human animal infections and risk surveillance group (HAIRS) at the Health Protection Agency.

The BSE inquiry was set up in January 1998 to look at the how the emergence and identification of BSE in cattle and new vCJD in humans in the UK was handled.

The inquiry highlighted the need to clearly communicate risk to the public and to the experts responsible for controlling it. The HAIRS group was set up in 2004 in an effort to improve the process for picking up new infections, assessing the risk and making the appropriate response.

With most new infections coming from animals, controlling them relies on collaboration between human and animal health. In addition to the HPA, HAIRS members include the Department for the Environment, Food and Rural Affairs, the Veterinary Laboratories Agency, the Food Standards Agency, the Department of Health, the chair of the expert panel on emerging infections, plus representatives from Scotland, Wales and Northern Ireland.

The group meets monthly and has a clear system for identifying and assessing zoonotic or potentially zoonotic infectious incidents that might pose a threat to public health in the UK.

“This is our main group for detecting and assessing threats from new and emerging infections, most of which are zoonoses,” says Dr Morgan.

The group’s first report, published in 2008, lists some of the issues discussed from 2004-07. All zoonotic infections are a concern because they should be preventable, says Dr Morgan. But she adds that it is difficult to make a list of the infections of primary concern because it is hard in public health terms to balance the consequences of infections that affect many people but cause mild illness with ones that infect few but cause severe illness.

“It is difficult because people do get very anxious about things that we can see are a low risk and yet they’re very unconcerned about things that are all around them and are much higher risk,” says Dr Morgan. “How do you balance a handful [of cases of] a horrendous illness in young people, which will kill you, like vCJD, against campylobacter and salmonella, which still cause high rates of hospitalisation and some deaths in England and Wales? Is it numbers, is it severity, is it the political interest? We do spend an awful lot of time on things which really have a low impact on public health because the public or others are concerned.”

Dr Morgan is keener on preparing for newer or unrecognised infections. The HPA has established good relationships with veterinary colleagues in England and within the devolved administrations and has a very low threshold for discussing or assessing any risk that they may feel might pose a nationwide threat to human health.

The HAIRS group discusses anything strange in animals, does a rapid risk assessment and tells policy makers. Dr Morgan says: “We have representatives of all the major agencies and government departments in the group; they will cascade upwards through their chain of command.”

And if a new infection has been identified around a certain type of pet, the group will work with pet interest groups and inform people that it may be a risk.

Once an infection has become established, the experts can come up with a plan for treating it. How long that takes depends on the level of knowledge. “Where we’re dealing with things like, let’s say, a new strain of flu, we know a lot already so although there’s often a lot of uncertainty to begin with we can usually formulate a plan fairly quickly once we know what we’re dealing with,” explains Professor Whitty. “Of course from time to time we will get an infection such as HIV, SARS or vCJD, which is completely unknown to us. And that will take a lot longer because we’re starting off from a completely blank sheet.”

Risk and reward

Given that zoonotic infections should be preventable, what can be done to stop them? “I think it’s just balancing up the risks and delights of having contact with animals,” says Dr Morgan. “People embrace the most unusual species without really thinking about the risks.”

Reptiles are getting more popular and a fairly unusual salmonella has been associated with them. In this case and in other cases of direct infection from animals, prevention comes down to good hygiene, which includes washing hands after contact with the animal.

For food-borne infections, the FSA promotes what it calls the four Cs, which are about cooking food thoroughly, chilling food properly, cleaning hands, surfaces and utensils after handling raw food, and avoiding cross contamination between raw and cooked foods.

The main food pathogens are Campylobacter, Salmonella, Listeria and E coli 0157, and are the FSA’s main focus.

“We need to separate those out from the very high-profile incidents where people make a connection with food, but there’s actually no risk there,” says Dr Linden Jack, who heads the FSA branch that is responsible for zoonotic infections. “For things such as avian flu or swine flu, transmission isn’t associated with properly handled or cooked products.”

From 2000-06 there was a 20 per cent reduction in laboratory reported cases of food poisoning. The FSA’s effort to reduce that further has three strands. First, action on the farm to reduce pathogens in the animals themselves. At the moment it is specifically targeting campylobacter in chickens and salmonella in pigs.

Dr Jack says: “If you can reduce the numbers in the animals themselves, you can reduce the burden on food handlers.”

The second strand is about better food safety management, which includes working with the catering sector, in particular providing support to small businesses, to ensure that the food they provide is safe. Improving the hygiene at slaughterhouses is another focus, and research is ongoing to identify practical ways that slaughterhouses can have a big impact in this area.

Third, the FSA works with consumers through its hygiene campaigns, which includes work in schools and other settings.

Each of the three strands is important and they all work together to help reduce food-borne disease.

But Dr Jack says: “If you look at it logically, the ultimate control is at the end of the chain when, if people handle and cook the food properly, then they will avoid food poisoning. But if we can do anything earlier in the chain to help them, that supports what they’re doing.”

When it comes to identifying new infections the main preventive measure for the public is to tell their GP about any infection they have that doesn’t quite make sense. It particularly applies to people who have travelled, who live in a rural area or who have pets.

NHS managers need to encourage health professionals to take time to ask about travel and contact with animals. Professor Whitty says: “It’s by early reporting that we’ll get ahead of the curve in terms of picking up infections early and dealing with them.”