Explainer: what is Murray Valley encephalitis virus?


Ana Ramírez, James Cook University; Andrew Francis van den Hurk, The University of Queensland; Cameron Webb, University of Sydney, and Scott Ritchie, James Cook University

Western Australian health authorities recently issued warnings about Murray Valley encephalitis, a serious disease that can spread by the bite of an infected mosquito and cause inflammation of the brain.

Thankfully, no human cases have been reported this wet season. The virus that causes the disease was detected in chickens in the Kimberley region. These “sentinel chickens” act as an early warning system for potential disease outbreaks.

What is Murray Valley encephalitis virus?

Murray Valley encephalitis virus is named after the Murray Valley in southeastern Australia. The virus was first isolated from patients who died from encephalitis during an outbreak there in 1951.

The virus is a member of the Flavivirus family and is closely related to Japanese encephalitis virus, a major cause of encephalitis in Asia.

Murray Valley encephalitis virus is found in northern Australia circulating between mosquitoes, especially Culex annulirostris, and water birds. Occasionally the virus spreads to southern regions, as mosquitoes come into contact with infected birds that have migrated from northern regions.




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How serious is the illness?

After being transmitted by an infected mosquito, the virus incubates for around two weeks.

Most people infected don’t develop symptoms. But, if you’re unlucky, you could develop symptoms ranging from fever and headache to paralysis, encephalitis and coma.

Around 40% of people who develop symptoms won’t fully recover and about 25% die. Generally, one or two human cases are reported in Australia per year.

Since the 1950s, there have been sporadic outbreaks of Murray Valley encephalitis, most notably in 1974 and 2011. The 1974 outbreak was Australia-wide, resulting in 58 cases and 12 deaths.

It’s likely the virus has been causing disease since at least the early 1900s when epidemics of encephalitis were attributed to a mysterious illness called Australian X disease.

Traditional monitoring of mosquito-borne diseases relies on the collection of mosquitoes using specially designed traps baited with carbon dioxide.
Cameron Webb

Early warning system

Given the severity of Murray Valley encephalitis, health authorities rely on early warning systems to guide their responses.

One of the most valuable surveillance tools to date have been chooks because the virus circulates between birds and mosquitoes. Flocks of chickens are placed in areas with past evidence of virus circulation and where mosquitoes are buzzing about.

Chickens are highly susceptible to infection so blood samples are routinely taken and analysed to determine evidence of virus infection. If a chicken tests positive, the virus has been active in an area.

The good news is that even if the chickens have been bitten, they don’t get sick.

Mosquitoes can also be collected in the field using a variety of traps. Captured mosquitoes are counted, grouped by species and tested to see if they’re carrying the virus.

This method is very sensitive: it can identify as little as one infected mosquito in a group of 1,000. But processing is labour-intensive.




Read more:
How Australian wildlife spread and suppress Ross River virus


How can technology help track the virus?

Novel approaches are allowing scientists to more effectively detect viruses in mosquito populations.

Mosquitoes feed on more than just blood. They also need a sugar fix from time to time, usually plant nectar. When they feed on sugary substances, they eject small amounts of virus in their saliva.

This led researchers to develop traps that contain special cards coated in honey. When the mosquitoes feed on the cards, they spit out virus, which specific tests can then detect.

We are also investigating whether mosquito poo could be used to enhance the sugar-based surveillance system. Mosquitoes spit only tiny amounts of virus, whereas they poo a lot (300 times more than they spit).

This mosquito poo can contain a treasure trove of genetic material, including viruses. But we’re still working out the best way to collect the poo.

Mosquito poo, shown here after mosquitoes have fed on coloured honey, can be used to detect viruses like Murray Valley encephalitis.
Dagmar Meyer

Staying safe from Murray Valley encephalitis

There is no vaccine or specific treatment for the virus. Avoiding mosquito bites is the only way to protect yourself from the virus. You can do this by:

  • wearing protective clothing when outdoors

  • avoiding being outdoors when the mosquitoes that transmit the virus are most active (dawn and dusk)

  • using repellents, mosquito coils, insect screens and mosquito nets

  • following public health advisories for your area.

The virus is very rare and your chances of contracting the disease are extremely low, but not being bitten is the best defence.The Conversation

Ana Ramírez, PhD candidate, James Cook University; Andrew Francis van den Hurk, Medical Entomologist, The University of Queensland; Cameron Webb, Clinical Lecturer and Principal Hospital Scientist, University of Sydney, and Scott Ritchie, Professorial Research Fellow, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Why naming all our mozzies is important for fighting disease


File 20180223 108139 lvidlr.jpg?ixlib=rb 1.1
And you can be…Susan.
from http://www.shutterstock.com

Bryan Lessard, CSIRO

Notorious for spreading diseases like malaria and Zika virus overseas, mosquitoes contribute to thousands of cases of human disease in Australia each year. But only half of Australia’s approximately 400 different species of mosquitoes have been scientifically named and described. So how are scientists able to tell the unnamed species apart?

Climate change means population change

Mosquito populations and our ability to predict disease outbreaks are likely to change in the future. As climates change, disease-carrying mozzies who love the heat may spread further south into populated cities.

As human populations continue to grow in Australia, they will interact with different communities of wild animals that act as disease reservoirs, as well as different mosquito species that may be capable of carrying these diseases. The expansion of agricultural and urban water storages will also create new homes for mosquito larvae to mature, allowing mosquitoes to spread further throughout the country.




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Mosquito larvae need a body of water to mature in.
James Gathany, CDC

Agents of disease

Mosquitoes like the native Common Banded Mosquito (Culex annulirostris) are known to spread human diseases such as Ross River virus, Barmah Forest virus, Dengue fever and Murray Valley encephalitis.

It’s not the adult mosquito itself that causes the disease, but the viruses and other microbes that accumulate in the mosquito’s saliva and are injected into the bloodstream of the unsuspecting victim during feeding.

The mosquitoes that bite humans are female, requiring the proteins in blood to ripen their eggs and reach sexual maturity. Male mosquitoes, and females of some species, are completely vegetarian, opting to drink nectar from flowers, and are useful pollinators.

The life cycle of a mosquito.
from http://www.shutterstock.com



Read more:
Common Australian mosquitoes can’t spread Zika


The name game

Mosquitoes belong to the fly family Culicidae and are an important part of our biodiversity. There are more than 3,680 known species of mosquitoes in the world. Taxonomists, scientists who classify organisms, have been able to formally name more than 230 species in Australia.

The classification of Australian mosquitoes tapered off in the 1980s with the publication of the last volume of The Culicidae of the Australasian Region and passing of Dr Elizabeth Marks who was the most important contributor to our understanding of Australian mosquitoes.

She left behind 171 unique species with code numbers like “Culex sp No. 32”, but unfortunately these new species were never formally described and remained unnamed after her death. This isn’t uncommon in biodiversity research, as biologists estimate that we’ve only named 25% of life on earth during a time when there is an alarming decline in the taxonomic workforce.

Dr Marks’ unnamed species are still held in Australian entomology collections, like CSIRO’s Australian National Insect Collection, Museum Victoria and the Queensland Museum. Although all the major disease-carrying species of mosquitoes are known in the world, several of Marks’ undescribed Australian species are blood feeding and may have the capacity to transmit diseases.

How do we tell mozzies apart?

Naming, describing and establishing the correct classification of Australia’s mosquitoes is the first step to understanding their role in disease transmission. This is difficult work as adults are small and fragile, and important diagnostic features that are used to tell species apart, like antennae, legs and even tiny scales, are easily lost or damaged.

CSIRO scientists, with support from the Australian Biological Resources Study, Government of Western Australia Department of Health, and University of Queensland, have been tasked with naming Australia’s undescribed mosquitoes. New species will be named and described based on the appearance of the adults and infant larval stages which are commonly intercepted by mozzie surveillance officers. New identification tools will also be created so others can quickly and reliably identify the Australian species.

A 100 year old specimen of the native Common Banded Mosquito Culex annulirostris, capable of spreading Murray Valley encephalitis virus, one of 12 million specimens held in CSIRO’s Australian National Insect Collection in Canberra.
CSIRO/Dr Bryan Lessard



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Scientists are now able to extract DNA and sequence the entire mitochondrial genome from very old museum specimens. CSIRO are using these next generation techniques to generate a reliable DNA reference database of Australian mosquitoes to be used by other researchers and mozzie surveillance officers to accurately identify specimens and diagnose new species. CSIRO are also digitising museum specimens to unlock distribution data and establish the geographical boundaries for the Australian species.

By naming and describing new species, we will gain a more complete picture of our mosquito fauna, and its role in disease transmission. This will make us better prepared to manage our mosquitoes and human health in the future as the climate changes and our growing human population moves into new areas of Australia.The Conversation

Bryan Lessard, Postdoctoral Research Fellow, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Mozzie repellent clothing might stop some bites but you’ll still need a cream or spray



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Clothes can offer some protection.
John Jones/Flickr, CC BY

Cameron Webb, University of Sydney

A range of shirts, pants, socks and accessories sold in specialist camping and fishing retailers claim to protect against mosquito bites for various periods.

In regions experiencing a high risk of mosquito-borne disease, insecticide treated school uniforms have been used to help provide extra protection for students.

During the 2016 outbreak of Zika virus in South America, some countries issued insecticide-treated uniforms to athletes travelling to the Olympic Games.

Some academics have even suggested fashion designers be encouraged to design attractive and innovative “mosquito-proof” clothing.




Read more:
The best (and worst) ways to beat mosquito bites


But while the technology has promise, commercially available mosquito-repellent clothing isn’t the answer to all our mozzie problems.

Some items of clothing might offer some protection from mosquito bites, but it’s unclear if they offer enough protection to reduce the risk of disease. And you’ll still need to use repellent on those uncovered body parts.

First came mosquito-proof beds

Bed nets have been used to create a barrier between people and biting mosquitoes for centuries. This was long before we discovered mosquitoes transmitted pathogens that cause fatal and debilitating diseases such as malaria. Preventing nuisance-biting and buzzing was reason alone to sleep under netting.

Bed nets have turned out to be a valuable tool in reducing malaria in many parts of the world. And they offer better protection if you add insecticides.

The insecticide of choice is usually permethrin. This and other closely related synthetic pyrethroids are commonly used for pest control and have been assessed as safe for use by the United States Environmental Protection Authority, the Australian Pesticides and Veterinary Medicines Authority and other regulatory bodies.




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New technologies have also allowed for the development of long-lasting insecticidal bed nets, offering extended protection against mosquito bites, perhaps up to three years, even with repeated washing.

Mosquito repellent clothing

Innovations in clothing that prevent insect bites have primarily come from the United States military. Mosquito-borne disease is a major concern for military around the globe. Much research funding has been invested in strategies to provide the best protection for personnel.

Traditional insect repellents, such as DEET or picaridin, are applied to the skin to prevent mosquitoes from landing and biting.

While permethrin will repel some mosquitoes, treated clothing most effectively works by killing the mosquitoes landing and trying to bite through the fabric.

Clothing treated with permethrin has been shown to protect against mosquitoes and ticks, as well as other biting insects and mites. For these studies, clothing was generally soaked in solutions or sprayed with insecticides to ensure adequate protection.

Clothing made from insecticide impregnated fabrics may help reduce mosquito bites.
Cameron Webb (NSW Health Pathology)

Fabrics factory-treated with insecticides, as used by many military forces, are purported to provide more effective protection. But while some studies suggest clothing made from these fabrics provide protection even after multiple washes, others suggest the “factory-treated” fabrics don’t provide greater levels of protection than “do it yourself” versions.

Overall, the current evidence suggests insecticide-treated clothing may reduce the number of mosquito bites you get, but it doesn’t offer full protection.

More research is needed to determine if insecticide-treated clothing can prevent or reduce rates of mosquito-borne disease.

Better labelling and regulation

All products that claim to provide protection from insect bites must be registered with the Australian Pesticides and Veterinary Medicines Authority. This includes sprays, creams and roll-on formulations of repellents.

Anything labelled as “insect repelling”, including insecticide treated clothing, requires registration. Clothing marketed as simply “protective” (such as hats with netting) doesn’t. This approach reflects the requirements of the US EPA.




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If you’re shopping for insect-repellent clothing, check the label to see if it states that it is registered by the APVMA. You should see a registration number and the insecticide used in the fabric clearly displayed on the clothing’s tag.

While some products will be registered, there are still some concerns about how the efficacy of mosquito bite protection is assessed.

There is likely to be growing demand for these types of products and experts are calling for internationally accepted guidelines to test these products. Similar guidelines exist for topical repellents.

Finally, keep in mind that while various forms of insecticide-treated clothing will help reduce the number of mosquito bites, they won’t provide a halo of bite-free protection around your whole body.

Remember to apply a topical insect repellent to exposed areas of skin, such as hands and face, to ensure you’re adequately protected from mosquito bites.The Conversation

Cameron Webb, Clinical Lecturer and Principal Hospital Scientist, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Lord of the forest: New Zealand’s most sacred tree is under threat from disease, but response is slow



File 20180725 194158 b7f6m9.jpg?ixlib=rb 1.1
Tāne Mahuta is New Zealand’s most sacred tree, but its days will be numbered if it is infected with kauri dieback disease.
from http://www.shutterstock.com, CC BY-SA

Matthew Hall, Victoria University of Wellington

Tāne Mahuta is Aotearoa New Zealand’s largest living being – but the 45m tall, 2,500-year-old kauri tree is under severe threat from a devastating disease.

Nearly a decade after the discovery of kauri dieback disease, it is continuing to spread largely unchecked through the northern part of the North Island. Thousands of kauri trees have likely been infected and are now dead or dying. The Waipoua forest, home of Tāne Mahuta and many other majestic kauri, is reported to be one of the worst affected areas.

For Māori, who trace their whakapapa (lineage) to the origins of the earth, Tāne Mahuta is kin. The threat of losing this tree should electrify the fight against kauri dieback.




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Call to close the forest

Named after Tāne, the son of Ranginui the sky father and Papatūanuku the earth mother, Tāne Mahuta is a highly revered taonga, or treasure. In Māori mythology, it was Tāne who brought trees and birds to earth.

The loss of this ancestor, with a presence that has been known to move some to tears, is incalculable.

Kauri dieback has been recorded metres from this ancient tree, despite the best efforts of a prevention programme that has been in place since 2009. Much of the focus of the programme has been on encouraging behaviour change by forest users (following paths, washing boots) and upgrading tracks (from mud to boardwalks). A new national pest management plan proposes more of the same.

As part of a prevention programme to limit the spread of kauri dieback, visitors to kauri forests are encouraged to spray their shoes with a disinfectant.
Eli Duke/WIkimedia Commons, CC BY-SA
Signs remind visitors in the Waitākere Ranges about precautions against the spread of kauri dieback disease.
from Wikimedia Commons, CC BY-SA

In my view, the most notable, and frustrating, aspect of this programme is the significant resistance to close kauri forest tracks to people, who, along with wild pigs, are one of the major vectors of the disease.

Te Kawerau ā Maki, a Māori tribal group with mana whenua (customary authority) over the land of the Waitākere forest in the Auckland region, have maintained a consistent stance that the only way to protect kauri forests is to close them to humans. In November 2017, they placed a rāhui (temporary closure) over the entire forest area, severely frustrated by the lack of effective action to control kauri dieback by Auckland Council.

A rāhui is not legally enforceable, and it was largely ignored by forest users who continued to enter and spread the disease. Eventually, six months later, Auckland Council voted to close the majority of tracks, but Te Kawerau ā Maki have viewed this as too little, and possibly too late.

Keeping the forest open

In a similar laggardly vein, the Department of Conservation has only just put forward a proposal to close or partially close 24 kauri forest tracks. This proposal is currently going through a consultation process, which seems inappropriate when dealing with an immediate biosecurity crisis.

The proposal does not include the Waipoua forest and the track that leads to Tāne Mahuta, or to other significant kauri such as Te Matua Ngahere. The department says:

the decision to propose track closures is not taken lightly, but has been considered in situations where there is high kauri dieback risk, low visitor use, high upgrade and ongoing maintenance costs, and a similar experience provided in the vicinity.

Tāne mahuta draws hundreds of thousands of tourists to the Waipoua forest area. This, combined with the fact that forest tracks are generally in good condition has led to the decision to keep the forest open. For now, the tangata whenua (local Māori with authority over land) support it.

Tāne Mahuta draws hundreds of thousands of visitors to the kauri forests in the north of New Zealand.
from http://www.shutterstock.com, CC BY-SA

Relinquishing our claims

Although we know that our human presence in kauri forests will lead to the certain death of the trees, many people still wish to venture into the forests, to walk or to hunt, regardless of the consequences.

Whether conscious or not, the value assessment here must be that the right of kauri trees to live and flourish is of lesser value than some fleeting recreation on a weekend afternoon. As people kept blindly tramping into the Waitākere forest, infection rates increased from 8% to 19% in just five years.

What I find most disturbing here is that government agencies tasked with preserving the “intrinsic values” of native species are prepared to let this happen for pragmatic and economic reasons. This is one of those situations where competing values can’t be balanced.

The life and flourishing of kauri must be prioritised above all else, whatever the economic or recreational hit. This means letting go of our claim to kauri trees as “natural and recreational resources” and acknowledging them for what they are – our living, spiritual, intelligent kin.

Kauri or kiwifruit

Pragmatically, our assistance to kauri also necessitates that we re-assess the value we place on the survival of kauri from an economic perspective.

Funding of less than NZ$2 million per year for the kauri dieback programme pales in comparison to the magnitude of the response to recent agricultural biosecurity threats.

In 2010, a huge response to the incursion of a microbial pathogen (Pseudomonas syringae pv. actinidiae, or Psa) in kiwifruit vines saw a NZ$50 million fund created to fight the disease.

In 2015, after a single Queensland fruit fly was caught in a trap in February, a large coordinated response, with local, restrictive biosecurity control orders in place, resulted in eradication in October, at a cost of NZ$13.6 million.

With such funds, it would be much easier to enforce the closure of kauri forests, until more long-term measures, such as improving genetic resistance, become possible.

At the end of last year, Minister for Forestry Shane Jones was quoted expressing a similar opinion, following the government’s announcement that it would attempt to eradicate the cow disease Mycoplasma bovis.

If it’s possible for us to move swiftly and cull diseased cows and stop the transport of potentially diseased cows off private farms, we need a similar level of vigour in safeguarding areas where our kauri are still strong.

The ConversationFor the survival of Tāne Mahuta, we should close off kauri forests immediately and boost funding for the implementation of the dieback management programme.

Matthew Hall, Associate Director, Research Services, Victoria University of Wellington

This article was originally published on The Conversation. Read the original article.

Some tropical frogs may be developing resistance to a deadly fungal disease – but now salamanders are at risk



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Panamanian golden frogs (Atelopus zeteki) are listed as critically endangered, and may be extinct in the wild.
Jeff Kubina, CC BY-SA

Louise Rollins-Smith, Vanderbilt University

My office is filled with colorful images of frogs, toads and salamanders from around the world, some of which I have collected over 40 years as an immunologist and microbiologist, studying amphibian immunity and diseases. These jewels of nature are mostly silent working members of many aquatic ecosystems.

The exception to the silence is when male frogs and toads call to entice females to mate. These noisy creatures are often wonderful little ventriloquists. They can be calling barely inches from your nose, and yet blend so completely into the environment that they are unseen. I have seen tropical frogs in Panama and native frogs of Tennessee perform this trick, seemingly mocking my attempts to capture them.

My current research is focused on interactions between amphibians and two novel chytrid pathogens that are linked to global amphibian declines. One, Batrachochytrium dendrobatidis ( abbreviated as Bd), has caused mass frog dieoffs around the world. Recently my lab group contributed to a study showing that some species of amphibians in Panama that had declined due to Bd infections are recovering. Although the pathogen has not changed, these species appear to have developed better skin defenses than members of the same species had when Bd first appeared.

This is very good news, but those who love amphibians need to remain vigilant and continue to monitor these recovering populations. A second reason for concern is the discovery of a closely related chytrid, Batrachochytrium salamandrivorans (Bsal), which seems to be more harmful to salamanders and newts.

Amphibian chytrid fungus has been detected in at least 52 countries and 516 species worldwide.
USDA Forest Service

Global frog decline

More than a decade ago, an epidemic of a deadly disease called chytridiomycosis swept through amphibian populations in Panama. The infection was caused by a chytrid fungus, Batrachochytrium dendrobatidis. Scientists from a number of universities, working with the Smithsonian Tropical Research Institute in Panama, reported that chytridiomycosis was moving predictably from west to east from Costa Rica across Panama toward Colombia.

I was part of an international group of scientists, funded by the National Science Foundation, who were trying to understand the disease and whether amphibians had effective immune defenses against the fungus. Two members of my lab group traveled to Panama yearly from 2004 through 2008, and were able to look at skin secretions from multiple frog species before and after the epidemic of chytridiomycosis hit.

Many amphibians have granular glands in their skin that synthesize and sequester antimicrobial peptides (AMPs) and other defensive molecules. When the animal is alarmed or injured, the defensive molecules are released to cleanse and protect the skin.

Through mechanisms that remain a mystery, we observed that these skin defenses seemed to improve after the pathogen entered the amphibian communities. Still, many frog populations in this area suffered severe declines. A global assessment published in 2004 showed that 43 percent of amphibian species were declining and 32 percent of species were threatened.

In Panama, Smithsonian scientists operate the largest amphibian conservation facility of its kind in the world.

Signs of resistance

In 2012-2013, my colleagues ventured to some of the same sites in Panama at which amphibians had disappeared. To our great delight, some of the species were partially recovering, at least enough so that they could be found and sampled again.

We wanted to know whether this was happening because the pathogen had become less virulent, or for some other reason, including the possibility that the frogs were developing more effective responses. To find out, we analyzed multiple measures of Bd‘s virulence, including its ability to infect frogs that had never been exposed to it; its rate of growth in culture; whether it had undergone genetic changes that would show loss of some possible virulence characteristics; and its ability to inhibit frogs’ immune cells.

As our group recently reported, we found that the pathogen had not changed. However, we were able to show that for some species, frog skin secretions we collected from frogs in populations that had persisted were better able to inhibit the fungus in a culture system than those from frogs that had never been exposed to the fungus.

The prospect that some frog species in some places in Panama are recovering in spite of the continuing presence of this virulent pathogen is fantastic news, but it is too soon to celebrate. The recovery process is very slow, and scientists need to continue monitoring the frogs and learn more about their immune defenses. Protecting their habitat, which is threatened by deforestation and water pollution, will also be a key factor for the long-term survival of these unique amphibian species in Panama.

If Bsal fungus spreads to North America, it could wipe out species like this Northern Slimy Salamander (Plethodon glutinosus).
Marshal Hedin, CC BY

Salamanders (and frogs) at risk

On a global scale, Bd is not the only threat. A second pathogenic chytrid fungus called Batrachochytrium salamandrivorans (abbreviated as Bsal) was recently identified in Europe, and has decimated some salamander populations in the Netherlands and Belgium. This sister species probably was accidentally imported into Europe from Asia, and seems to be a greater threat to salamanders than to frogs or toads.

Bsal has not yet been detected in North America. I am part of a new consortium of scientists that has formed a Bsal task force to study whether it could become invasive here, and which species might be most adversely affected.

In January 2016 the U.S. Fish and Wildlife Service listed 201 salamander species as potentially injurious to wildlife because of their their potential to introduce Bsal into the United States. This step made it illegal to import or ship any of these species between the continental United States, the District of Columbia, Hawaii, the Commonwealth of Puerto Rico or any possession of the United States.

The Bsal task force is currently developing a strategic plan that lists the most urgent research needs to prevent accidental introduction and monitor vulnerable populations. In October 2017 a group of scientists and conservation organizations urged the U.S. government to suspend all imports of frogs and salamanders to the United States.

The ConversationIn short, it is too early to relax. There also are many other potential stressors of amphibian populations including climate change, decreasing habitats and disease. Those of us who cherish amphibian diversity will continue to worry for some time to come.

Louise Rollins-Smith, Associate Professor of Pathology, Microbiology and Immunology, Vanderbilt University

This article was originally published on The Conversation. Read the original article.

11 billion pieces of plastic bring disease threat to coral reefs



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A plastic bottle trapped on a coral reef.
Tane Sinclair-Taylor, Author provided

Joleah Lamb, Cornell University

There are more than 11 billion pieces of plastic debris on coral reefs across the Asia-Pacific, according to our new research, which also found that contact with plastic can make corals more than 20 times more susceptible to disease.

In our study, published today in Science, we examined more than 124,000 reef-building corals and found that 89% of corals with trapped plastic had visual signs of disease – a marked increase from the 4% chance of a coral having disease without plastic.

Globally, more than 275 million people live within 30km of coral reefs, relying on them for food, coastal protection, tourism income, and cultural value.

With coral reefs already under pressure from climate change and mass bleaching events, our findings reveal another significant threat to the world’s corals and the ecosystems and livelihoods they support.




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In collaboration with numerous experts and underwater surveyors across Indonesia, Myanmar, Thailand and Australia, we collected data from 159 coral reefs between 2010 and 2014. In so doing, we collected one of the most extensive datasets of coral health in this region and plastic waste levels on coral reefs globally.

There is a huge disparity between global estimates of plastic waste entering the oceans and the amount that washes up on beaches or is found floating on the surface.

Our research provides one of the most comprehensive estimates of plastic waste on the seafloor, and its impact on one of the world’s most important ecosystems.

Plastic litter in a fishing village in Myanmar.
Kathryn Berry

The number of plastic items entangled on the reefs varied immensely among the different regions we surveyed – with the lowest levels found in Australia and the highest in Indonesia.

An estimated 80% of marine plastic debris originates from land. The variation of plastic we observed on reefs during our surveys corresponded to the estimated levels of plastic litter entering the ocean from the nearest coast. One-third of the reefs we surveyed had no derelict plastic waste, however others had up 26 pieces of plastic debris per 100 square metres.

We estimate that there are roughly 11.1 billion plastic items on coral reefs across the Asia-Pacific. What’s more, we forecast that this will increase 40% in the next seven years – equating to an estimated 15.7 billion plastic items by 2025.

This increase is set to happen much faster in developing countries than industrialised ones. According to our projections, between 2010 and 2025 the amount of plastic debris on Australian coral reefs will increase by only about 1%, whereas for Myanmar it will almost double.

How can plastic waste cause disease?

Although the mechanisms are not yet clear, the influence of plastic debris on disease development may differ among the three main global diseases we observed to increase when plastic was present.

Plastic debris can open wounds in coral tissues, potentially letting in pathogens such as Halofolliculina corallasia, the microbe that causes skeletal eroding band disease.

Plastic debris could also introduce pathogens directly. Polyvinyl chloride (PVC) – a very common plastic used in children’s toys, building materials like pipes, and many other products – have been found carrying a family of bacteria called Rhodobacterales, which are associated with a suite of coral diseases.

Similarly, polypropylene – which is used to make bottle caps and toothbrushes – can be colonised by Vibrio, a potential pathogen linked to a globally devastating group of coral diseases known as white syndromes.

Finally, plastic debris overtopping corals can block out light and create low-oxygen conditions that favour the growth of microorganisms linked to black band disease.

Plastic debris floating over corals.
Kathryn Berry

Structurally complex corals are eight times more likely to be affected by plastic, particularly branching and tabular species. This has potentially dire implications for the numerous marine species that shelter under or within these corals, and in turn the fisheries that depend on them.




Read more:
Eight million tonnes of plastic are going into the ocean each year


Our study shows that reducing the amount of plastic debris entering the ocean can directly prevent disease and death among corals.

The ConversationOnce corals are already infected, it is logistically difficult to treat the resulting diseases. By far the easiest way to tackle the problem is by reducing the amount of mismanaged plastic on land that finds its way into the ocean.

Joleah Lamb, Research fellow, Cornell University

This article was originally published on The Conversation. Read the original article.

Why we shouldn’t be too quick to blame migratory animals for global disease


Alice Risely, Deakin University; Bethany J Hoye, University of Wollongong, and Marcel Klaassen, Deakin University

Have you ever got on a flight and the person next to you started sneezing? With 37 million scheduled flights transporting people around the world each year, you might think that the viruses and other germs carried by travellers would be getting a free ride to new pastures, infecting people as they go.

Yet pathogenic microbes are surprisingly bad at expanding their range by hitching rides on planes. Microbes find it difficult to thrive when taken out of their ecological comfort zone; Bali might just be a tad too hot for a Tasmanian parasite to handle.

But humans aren’t the only species to go global with their parasites. Billions of animals have been flying, swimming and running around the globe every year on their seasonal migrations, long before the age of the aeroplane. The question is, are they picking up new pathogens on their journeys? And if they are, are they transporting them across the world?


Read more: A tale of three mosquitoes: how a warming world could spread disease


Migratory animals are the usual suspects for disease spread

With the rate of zoonotic diseases (pathogens that jump from animals to humans) on the rise, migratory animals have been under increasing suspicion of aiding the spread of devastating diseases such as bird flu, Lyme disease, and even Ebola.

These suspicions are bad for migrating animals, because they are often killed in large numbers when considered a disease threat. They are also bad for humans, because blaming animals may obscure other important factors in disease spread, such as animal trade. So what’s going on?

Despite the logical link between animal migration and the spread of their pathogens, there is in fact surprisingly little direct evidence that migrants frequently spread pathogens long distances.

This is because migratory animals are notoriously hard for scientists to track. Their movements make them difficult to test for infections over the vast areas that they occupy.

But other theories exist that explain the lack of direct evidence for migrants spreading pathogens. One is that, unlike humans who just have to jump on a plane, migratory animals must work exceptionally hard to travel. Flying from Australia to Siberia is no easy feat for a tiny migratory bird, nor is swimming between the poles for giant whales. Human athletes are less likely to finish a race if battling infections, and likewise, migrant animals may have to be at the peak of health if they are to survive such gruelling journeys. Sick travellers may succumb to infection before they, or their parasitic hitchhikers, reach their final destination.

Put simply, if a sick animal can’t migrate, then neither can its parasites.

On the other hand, migrants have been doing this for millennia. It is possible they have adapted to such challenges, keeping pace in the evolutionary arms race against pathogens and able to migrate even while infected. In this case, pathogens may be more successful at spreading around the world on the backs of their hosts. But which theory does the evidence support?

Sick animals can still spread disease

To try and get to the bottom of this question, we identified as many studies testing this hypothesis as we could, extracted their data, and combined them to look for any overarching patterns.

We found that infected migrants across species definitely felt the cost of being sick: they tended to be in poorer condition, didn’t travel as far, migrated later, and had lower chances of survival. However, infection affected these traits differently. Movement was hit hardest by infection, but survival was only weakly impacted. Infected migrants may not die as they migrate, but perhaps they restrict long-distance movements to save energy.

So pathogens seem to pose some costs on their migratory hosts, which would reduce the chances of migrants spreading pathogens, but perhaps not enough of a cost to eliminate the risk completely.


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But an important piece of the puzzle is still missing. In humans, travelling increases our risk of getting ill because we come into contact with new germs that our immune system has never encountered before. Are migrants also more susceptible to unfamiliar microbes as they travel to new locations, or have they adapted to this as well?

Guts of migrants resistant to microbial invasion

To investigate the susceptibility of migrants, we went in a different direction and decided to look at the gut bacteria of migratory shorebirds – grey, unassuming birds that forage on beaches or near water, and that undergo some of the longest and fastest migrations in the animal kingdom.

Most animals have hundreds of bacterial species living in their guts, which help break down nutrients and fight off potential pathogens. Every new microbe you ingest can only colonise your gut if the environmental conditions are to its liking, and competition with current residents isn’t too high. In some cases, it may thrive so much it becomes an infection.

The Red-necked stint is highly exposed to sediment microbes as it forages for the microscopic invertebrates that fuel its vast migrations.
Author provided

We found the migratory shorebirds we studied were exceptionally good at resisting invasion from ingested microbes, even after flying thousands of kilometres and putting their gut under extreme physiological strain. Birds that had just returned from migration (during which they stopped in many places in China, Japan, and South East Asia), didn’t carry any more species of bacteria than those that had stayed around the same location for a year.

The ConversationAlthough these results need to be tested in other migratory species, our research suggests that, like human air traffic, pathogens might not get such an easy ride on their migratory hosts as we might assume. There is no doubt that migrants are involved in pathogen dispersal to some degree, but there is increasing evidence that we shouldn’t jump the gun when it comes to blaming migrants.

Alice Risely, PhD candidate in Ecology, Deakin University; Bethany J Hoye, Lecturer in Animal Ecology, University of Wollongong, and Marcel Klaassen, Alfred Deakin Professor and Chair in Ecology, Deakin University

This article was originally published on The Conversation. Read the original article.