On the Horizon: The spread of Lassa fever

On the Horizon is the Society’s blog series on emerging and re-emerging infectious diseases. For this article, we spoke to Dr Lina Moses from Tulane University in New Orleans about Lassa fever, a viral infection spreading across parts of West Africa.

A transmission electron micrograph (TEM) of a number of Lassa virus virions adjacent to some cell debris

Lassa fever is thought to kill around 5,000 people across West Africa each year. The disease is caused by a virus, and usually begins with a mild fever along with weakness and headache. But in around a fifth of cases, symptoms are more serious, including vomiting, severe haemorrhaging (from the gums, eyes or nose), and death.

The early symptoms of Lassa fever are similar to many other diseases, like flu and malaria, which means that for many people, by the time they are diagnosed, it’s too late.

The ‘Lassa season’, which normally runs from November to February, is continuing for longer this year. Cases of Lassa fever are on the rise across West Africa, but Nigeria in particular is experiencing an especially deadly outbreak. According to the WHO, the country has seen over 270 reported cases and 149 deaths since August 2015. Increased vigilance and better detection in the wake of the Ebola outbreak may partly be responsible for the increase in reported cases, but the death rate for the current outbreak seems to be much higher than the usual 1–15%. The reasons for this remain unclear

Lassa fever is spread by the multimammate rat (Mastomys natalensis). These rodents are extremely common in West Africa, breeding quickly and in large numbers. But exactly how people tend to interact with rats, and how the virus is most easily transmitted (through urine, faeces, blood, or eating rats that are sometimes caught for food) isn’t really known.

Multimammate rat, Kelly et al under CC-BY-3.0 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3562201/

Dr Lina Moses is a researcher at Tulane University trying to understand what happens at the rodent–human interface in Sierra Leone, another country with endemic Lassa fever. Her work attempts to unravel the factors and behaviours that may prevent or enhance transmission of the disease.

“There isn’t really an age group or sex at higher risk [of contracting Lassa] that we’ve identified,” explains Lina. “We don’t know if it’s during agricultural practices or inside households that transmission occurs. Many of the men, women and children are subsistence farmers, so it’s hard to figure out where people are getting exposed.”

Lina has also been developing community interventions for rodent control in Sierra Leone. It’s not possible to rid the villages of rats completely, but the aim is to reduce populations enough to break the cycle of transmission to humans. The aim of the project is to see which methods are most effective at controlling rodents, and which get the most buy-in from locals.

“People like to trap rats. I think the main reason is that it’s mentally measurable to them, they can see that a rodent is being removed from their house,” Lina says. “But there’s some risk [of infection] there in terms of handling the rodents.”

One potential solution is to use local, disposable traps made from branches, leaves and twine, instead of Western traps made from plastic or metal. Local traps are cheap, sustainable and effective, and can be destroyed safely after use.

According to Lina’s research, people are less enthusiastic about preventative measures to keep rats away in the first place. This may be partly because such measures are perceived as less effective, or because continuous rodent control is simply low down on people’s priority lists.

“In Kenema district where we work, most people know that Lassa is a serious disease, and around half of them know that it’s spread by rats,” explains Lina. “But it’s all about priorities – sometimes getting food on the table is more important. And people have a lot of other health priorities, like malaria, which can be severe in small children,” says Lina.

The sheer number of rodents in the land around villages also means it’s extremely difficult to stop them from entering people’s homes – and the living conditions faced by most don’t help. “I sympathise, because even my house in New Orleans with access to proper storage, I’ll delay doing the dishes for example,” says Lina. “It’s challenging in Sierra Leone because they don’t have cabinets, and often can’t afford nice metal or plastic containers for food.”

As well as this, many villagers in Sierra Leone are rice farmers, and it’s common for people to store the entire day’s harvest inside their homes to prevent theft. But leaving this much rice indoors is almost guaranteed to attract rodents, and it’s difficult to find a drum or container large enough to store it.

“There are solutions that don’t require a whole lot of resources,” says Lina. “Some people build rice barns, which are essentially like houses but raised, with cones wrapped around the posts to stop rats climbing up.” Having a rice barn to store a harvest can be very effective. Ideally, several families could share a rice barn together and use it to store their rice harvest, but this requires both money and trust.

There is one other method of rodent control that’s particularly intriguing – cats. Lina says in one village that passed a law requiring every house to have a cat (and another prohibiting anyone from eating a cat, which does happen from time to time), the number of Mastomys rats fell dramatically. And since the laws were passed, there have been no more cases of Lassa transmission.

“Cats are very effective at reducing rodent populations, but we don’t know if Lassa virus can spread to cats or if cats can transmit Lassa to humans,” says Lina. “So unfortunately we didn’t look at cats in our interventions – although it might end up being the biggest thing.” (Interestingly, the WHO still recommends keeping a cat as a way to prevent infection).

At the moment, there is no vaccine for Lassa fever, although there are candidates waiting for clinical trials. But because the main route of transmission is from rats, and Lassa isn’t transmitted very efficiently between humans (unlike Ebola, for example), rodent control will always be a part of the solution, even if a successful vaccine is developed.

“Rodent vaccines could also be useful, if they were cheap,” says Lina. “But rodents have a shorter life expectancy and faster reproductive rates than humans, so that would have to be done regularly. If we want to reduce the burden of Lassa, we have to come at it from many different angles.”

Anand Jagatia

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Exploring Open Data: The Importance of Sustained Sequencing

Open-DataOpen data has the potential to revolutionise microbial genomics.  But in practice, many of the benefits of this technology remain untapped. So how can we achieve greater data sharing? Over the coming weeks, we’ll be featuring some highlights from a panel discussion on open data at the Annual Conference 2016.

In this video Professor Paul Kellam discusses the need for sustained sequencing of new pathogens. Genetic sequences are powerful tools, and releasing limited metadata can provide real insight into an epidemic without revealing the identity of individuals. Nevertheless, genome sequencing needs to be maintained and published after the initial rush to provide maximum benefit for public health.

Paul Kellam is a Professor of Virology at Imperial College London and at the Wellcome Trust Sanger Institute.

This panel was hosted by the PHG FoundationYou can read more about their approach to open data and their model for data sharing here.

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Cows on antibiotics release more methane from their dung

It’s a well-known fact that cattle and other livestock are responsible for releasing greenhouse gases like methane into the atmosphere. However, contrary to popular belief, it’s actually bovine burps, not farts, that are to blame. Methane from belching is a serious problem, accounting for 25% of  total man-made emissions.

The gases themselves are produced by gut microbes that help cows to digest the tough plant material that makes up their diet. The micro-organisms produce nutrients for the cow, spewing out waste gases like methane, carbon dioxide and nitrous oxide in the process.

But these microbes are also found in cow faeces, meaning that dung continues to emit greenhouse gases long after it passes out of the cow.

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Exploring Open Data: Outbreak Surveillance on an International Scale

Open-DataOpen data has the potential to revolutionise microbial genomics.  But in practice, many of the benefits of this technology remain untapped. So how can we achieve greater data sharing? Over the coming weeks, we’ll be featuring some highlights from a panel discussion on open data at the Annual Conference 2016.

This week, Dr Nick Loman from the University of Birmingham discusses the effects of sharing genomic data in real time on a specific outbreak of Salmonella enteritidis in the UK. Through this sharing of genomic datasets, researchers were able to confirm that the cases were linked to a larger, national-scale outbreak, all linking to the same source. Continue reading

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On the Horizon: an introduction

Earth from spaceOver the next few weeks and months, we’ll be publishing a collection of articles about emerging diseases in our On the Horizon series. In this first post, we spoke to David Heymann, Professor of Infectious Disease Epidemiology at the London School of Hygiene and Tropical Medicine, about the risks and reasons that these diseases emerge.

In December 2015, the World Health Organization (WHO) held a workshop in Geneva attended by microbiologists, public health experts, medics and mathematicians, among others. The aim of this meeting was to come up with a list – one that prioritised the emerging diseases that were most likely to cause large-scale outbreaks in the future. Of course, predicting which diseases may become problematic is difficult – just how serious the current Zika outbreak would become was unclear when this meeting was taking place.

This current list contains eight diseases, some you’ve heard of – like Ebola – and others that you may not have – Nipah virus, for example. Over the next few weeks, we’ll be publishing a series of articles about some of these emerging diseases, which can affect humans, animals or plants. Continue reading

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Parliamentary Links Day 2016

Parliament and Portcullis HouseParliamentary Links Day, organised by the Royal Society of Biology on behalf of the science and engineering community, is an annual event that brings together the scientific community and Members of Parliament. The theme of this year’s meeting was ‘Science after the Referendum: What Next?’ and could not have been more relevant and timely following the referendum result just four days prior. The room was packed to capacity with the majority of attendees standing, reflecting the scientific community’s great interest in their future in these uncertain times.

The day included introductions and speeches from Members of Parliament, two panel discussions and closing addresses from Lord O’Neill and Sir Venki Ramakrishnan FRS, the President of the Royal Society.

The Speaker of the House of Commons, the Rt Hon John Bercow MP, started the day off by assuring the room that science is fundamental in the progression of the country and spans all political beliefs. This was followed up by the Minister of State for Universities and Science, Jo Johnson MP, who raised the question of how can we minimise the potential damage to science from leaving the European Union (EU) and maximise the opportunities. Continue reading

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Microbe Talk Extra: Killer Fungus

FCmn4HodW8AIAZU4.jpg-largeungal diseases cause an estimated 1.5 million deaths each year – more than malaria.  Despite this, fungi are often overlooked compared to other pathogens like bacteria and viruses.

In this extra edition of the podcast, we sent Anand Jagatia along to the Royal Society’s Summer Science Exhibition to find out more about the dangers of killer fungi, and the world’s biggest Petri dish…

To find out more, visit http://www.killerfungus.org

The Royal Society’s Summer Science Exhibition runs until the 10 July 2016. Entrance is free, and all details can be found on their website.

Anand Jagatia

Image Credit: Killer Fungus
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