̽��ֱ�� of Cambridge - zoonoses

Beyond the pandemic: reduce the risk of animal viruses jumping to humans

lw355 — Thu, 30 Jul 2020 07:40:07 +0000

Cambridge zoologists Bill Sutherland and Silviu Petrovan warn that we must dramatically change the way we interact with animals to reduce the risk of this happening again.

Pig-borne disease jumped into humans when rearing practices changed

cjb250 — Tue, 31 Mar 2015 09:00:00 +0000

Almost every pig carries harmless strains of the S. suis bacterium – such strains are known as ‘commensal’ strains. However, a more virulent group of strains of the bacteria also exist, which cause disease in pigs worldwide and are a major driver of antibiotic use for prevention. Increasingly, this group of strains is also implicated in serious human diseases such as meningitis and septicaemia.

In order to understand the genetic basis of disease in S. suis, an international study, led by the Bacterial Respiratory Diseases of Pigs-1 Technology (BRaDP1T) consortium, examined the genomes of 375 clinical samples from pigs and humans from the UK and Vietnam and combined these with data already published on 15 S. suis genome sequences and draft genomes from around the world. They found that the commensal strains and disease-causing strains differed genetically; in particular, the disease-causing strains have between 50 and 100 fewer genes than the commensal strains.

Dr Lucy Weinert from the Department of Veterinary Medicine at the ̽��ֱ�� of Cambridge, first author of the study, says: “It seems that the loss of genes is associated with causing disease. This is something we see quite often in bacteria, but for reasons that are unclear. One possibility is that the missing genes are those that hinder the function of newly-acquired virulence factors in the genomes.”

By examining the S. suis’s ‘tree of life’ – which looks at how the bacteria have evolved over time – the researchers were able to show that the emergence of a group of strains causing meningitis in pigs and the human form of the disease dates back to the 1920s, when pig production was intensified with the introduction of wide-scale indoor rearing of meat-producing pigs in larger groups, supported by government schemes that favoured larger producers with regular throughput. However, despite having jumped the species barrier from pig to human, the bacteria do not appear to have adapted to infect humans.

“A group of more virulent strains seem to have emerged at around the time the pig industry changed, and it is these strains that mostly cause disease in pigs and humans,” says Professor Duncan Maskell, Head of the School of the Biological Sciences at Cambridge.

“Human S. suis disease in the West is extremely rare, but is seen more frequently in south east Asia. It is most likely spread to humans through poor food hygiene practices or other environmental factors. This emphasises the importance of monitoring such practices and putting policies in place to reduce the risk of the spread of infections between species.”

̽��ֱ��study was primarily funded by the Biotechnology and Biological Sciences Research Council.

Reference
Weinert, LA et al. Genomic signatures of human and animal disease in the zoonotic pathogen Streptococcus suis. Nature Communications; 31 March 2015

̽��ֱ��most virulent strains of Streptococcus suis, the leading cause of bacterial meningitis in adult humans in parts of southeast Asia and in pigs around the world, are likely to have evolved and become widespread in pigs at the same time as changes in rearing practices, according to research from an international consortium published today in the journal Nature Communications.

A group of more virulent strains seem to have emerged at around the time the pig industry changed, and it is these strains that mostly cause disease in pigs and humans

Duncan Maskell

Balint Földesi

Pig Head

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Emerging diseases likely to be more harmful in similar species

cjb250 — Tue, 17 Mar 2015 13:00:28 +0000

A number of emerging infectious diseases – including some of the most deadly outbreaks such as Ebola, SARS and HIV – are the result of humans becoming infected with a pathogen that normally infects another species. ̽��ֱ��amount of harm caused by a pathogen when it jumps into a new species can be very variable, at times causing few, if any symptoms, while at other times causing high levels of mortality.

A team led by researchers at the Department of Genetics, ̽��ֱ�� of Cambridge, has looked at how the harm a pathogen causes can change following a jump between species. ̽��ֱ��researchers infected 48 species of fruit fly with an RNA virus, and found that the amount of harm caused by the virus was extremely variable in the new hosts, with some species having relatively benign infections and other species dying rapidly. Most of the deadly emerging diseases that infect humans are caused by RNA viruses.

̽��ֱ��different species of fruit fly shared a common ancestor around 40 million years ago. ̽��ֱ��relationships between the different species can be examined using an evolutionary ‘tree’ known as a phylogeny. Species that cluster together are the most genetically similar.

In a study published today in the journal PLOS Pathogens, the researchers show that closely related species show similar levels of virulence when infected with the virus, with the tree of species being a patchwork of closely related groups showing high or low virulence. ̽��ֱ��level of virulence observed appears to be due to the amount of virus that accumulates in the hosts. ̽��ֱ��viral load also likely affects the ability of the virus to spread.

Although the research was carried out in fruit flies, the researchers suggest that the general principle should be applicable across species. A study published in the journal Science in 2014 showed a pattern consistent with such effects in amphibians infected by chytrid fungus.

“We see such patterns in the wild,” explains Dr Ben Longdon. “ ̽��ֱ��Ebola virus, for example, appears to cause few symptoms in its natural reservoir, the fruit bat, but it is deadly in chimpanzees, gorillas and humans.

“While there may be no clear rule to predict how deadly a pathogen will be in a new host, a simple rule of thumb may be that if it causes high levels of virulence in any given host species, it will typically cause similar levels of virulence in closely-related hosts. If we see a new disease emerge that causes high levels of mortality in chimpanzees, for example, then it may also be a danger to humans.”

̽��ֱ��research was mainly funded by the European Research Council and the Natural Environment Research Council (NERC).

Reference
Longdon, B et al. ̽��ֱ��causes and consequences of changes in virulence following pathogen host shifts. PLOS Pathogens. 19 March 2015

When viruses such as influenza and Ebola jump from one species to another, their ability to cause harm can change dramatically, but research from the ̽��ֱ�� of Cambridge shows that it may be possible to predict the virus’s virulence by looking at how deadly it is in closely-related species.

A simple rule of thumb may be that if a pathogen causes high levels of virulence in any given host species, it will cause similar levels of virulence in closely-related hosts

Ben Longdon

CDC Global

Ebola virus

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Understanding the bushmeat market: why do people risk infection from bat meat?

cjb250 — Thu, 09 Oct 2014 10:00:00 +0000

̽��ֱ��Straw-Coloured Fruit Bat, Eidolon helvum, is widely hunted and eaten in Ghana, but carries a risk of infection with ‘zoonotic’ pathogens – diseases transmitted from animal to man. Hunting, butchering and consuming wild animals for food can potentially transmit these infections through bites, scratches, bodily fluids, tissue and excrement. Bats in particular appear to host more zoonotic viruses per species than any other group of mammals, yet very little is known about how humans and bats interact, how people perceive bats and their accompanying disease risk, or who is most at risk.

Dr Olivier Restif from the Department of Veterinary Medicine at the ̽��ֱ�� of Cambridge explains: “Knowing who eats bush meat and why, as well as how they perceive the risks, is important for informing both disease and conservation management plans. This requires a close-knit collaboration between epidemiologists, ecologists and social anthropologists. That is why we have teamed up with the Zoological Society of London and the ̽��ֱ�� of Ghana to develop this research programme.”

Dr Alexandra Kamins, a Gates Cambridge scholar alumna working with Dr Restif, adds: “All too often, local community voices go unheard, despite representing those most at risk of spillover and often shouldering negative impacts arising from intervention measures. That is why it was important for us to listen to them.”

Dr Kamins and colleagues interviewed 577 people across southern Ghana, including hunters, vendors and consumers of bat meat. Of these, the majority (551) were interviewed using a general survey whilst the rest were interviewed in-depth through focus groups.

̽��ֱ��researchers found that hunters used a variety of means to capture bats, including shooting, netting and scavenging, and that all of the hunters reported handling live bats, coming into contact with bat blood and getting scratched or bitten. None of the hunters reported using protective measures, such as gloves. Scavenged bats were collected alive, usually when a branch broke and bats fell to the ground, but this too carried risks: four interviewees explained how people would fight over the bats when a large branch fell, sometimes even lying down on top of bats to prevent others from taking them, often sustaining bites and scratches.

̽��ֱ��bats were prepared and cooked in a number of ways, the most common methods being to smoke the bats before preparing food and using the bats in soup. At odds with reports from other countries, the survey in South East Ghana revealed few uses of bat bushmeat associated with traditional beliefs or medical practices. In Ghana, bat bushmeat seems to function as both subsistence and luxury food. ̽��ֱ��large number of hunters who hunt for themselves or who keep some of their catch suggests that bats provide a readily available source of animal protein. At the same time, high taste ratings among consumers and relatively high prices suggest that bat meat is seen as a ‘luxury food’ in Ghana.

Hunters, vendors and consumers of bat meat all tended to be older than those people with no connection to the practice - on average seven to ten years older. ̽��ֱ��researchers believe this could imply a number of scenarios, the most likely being a decrease in youth interest in bat bushmeat.

They found a strong association between gender and roles in the bat-bushmeat commodity chain, with hunters primarily being male and vendors female, consistent with the cultural norms of rural Ghanaian society. This could mean that disease risk was also different between the sexes. ̽��ֱ��researchers also found that those people living in urban environments and those who were more educated were less likely to participate in bat bushmeat activities. Although this suggests that increased urbanisation and improvements in education could reduce the use of bats as bushmeat, it is possible that increased household income could lead to increased bushmeat consumption, particularly as the meat appears to be seen as a luxury item.

Using focus groups, the researchers carried out more in-depth interviews to understand participants’ likely reactions to interventions regarding bat bushmeat. They found that regulations by themselves are not effective solutions: laws and fines alone are unlikely to induce change. While only some of our respondents would be willing to risk paying fines if they continued to earn enough from selling bat bushmeat, essentially no one knew of the existing hunting laws in Ghana, suggesting that enforcement is a major issue.

Possible health risks appeared to be more of a deterrent than fines; some respondents suggested that disease risk could motivate them to stop. However, the risk of disease from bat bushmeat was considered to be greatest by those who did not consume the meat and lowest by those who hunted or sold the bats. This finding supports previous research suggesting that people can readily perceive risk and even intellectually acknowledge desire to reduce that risk, but actual behaviour might not change.

Professor James Wood, who leads the research programme at the ̽��ֱ�� of Cambridge, says: “Understanding both actual and perceived risk factors is vital. If a bat-borne zoonotic disease outbreak were to occur in Ghana, our information could prove invaluable in helping target those groups at greatest risk and in planning disease control measures.”

Dr Marcus Rowcliffe from ZSL adds: “Unfortunately, there may not be a simple way to minimise the risks of zoonotic spillover from bats. For example, bat hunting is a highly seasonal occupation and, like all bushmeat hunting, can be started and dropped at will, whereas rearing domestic animals – one possible sustainable solution for reducing bushmeat hunting – requires continuous activity throughout the year on a daily basis.

“Although many programmes suggest economic opportunity as the major motivation behind livelihood choices and success of alternatives, it may not be enough on its own. We found people in Ghana to be responsive to education pieces about the disease risk from bushmeat but also the ecological role of bats in pollination and seed dispersal. Working with local communities to help them find effective and sustainable solutions in line with their economic needs must be a long-term commitment.”

Reference
Kamins, AO et al. Characteristics and Risk Perceptions of Ghanaians Potentially Exposed to Bat-Borne Zoonoses through Bushmeat. Ecohealth; 30 Sept 2014

Ebola, as with many emerging infections, is likely to have arisen due to man’s interaction with wild animals – most likely the practice of hunting and eating wild meat known as ‘bushmeat’. A team of researchers led by the ̽��ֱ�� of Cambridge and the Zoological Society of London (ZSL) has surveyed almost six hundred people across southern Ghana to find out what drives consumption of bat bushmeat – and how people perceive the risks associated with the practice.

Knowing who eats bush meat and why, as well as how they perceive the risks, is important for informing both disease and conservation management plans

Olivier Restif

Arran ET

Straw coloured fruit bat (edit)

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