Archive for the ‘New research’ Category

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Zoonotic diseases – causing more problems than illnesses/deaths alone

July 26, 2012

ResearchBlogging.org 

@DiseaseMapper recently tweeted a link to a very interesting paper (which happily is also free to access so you can read it too – the link is here )

Why do I think this paper is so interesting?  Firstly, because it is a useful reminder that zoonotic infections (those that pass from animals to man and vice versa) do not just impact on our lives by causing us illness, and in the worst circumstance, death.  They have a massive economic impact as well.  In fact the paper reports that the estimated economic impact of zoonotic diseases from 1995-2008 was over 120 billion dollars.

There are many reasons for the economic burden of these diseases being so high: impact on tourism; impact on international trade agreements; impact on consumer consumption and behaviour; loss of farmed animals.  In many outbreaks the local economy is negatively impacted in multiple ways and obviously in poorer areas this can also secondarily affect people’s health.

The paper also goes on to speculate about why there should be a resurgence of zoonotic infections.  The authors split it into ‘Factors associated with human behaviour’; ‘Factors associated with pathogen characteristics’ and ‘Climate change and zoonotic resurgence’.  So, pinching their titles…

Factors associated with human behaviour

Here the authors split it down further:

Individual human practices – the authors use the example of ecotourism.  “urban citizens of the developed world who visit developing countries or rural areas of the developed world and engage in activities such as forest camping, river rafting, or bat cave exploring, are prone to zoonotic infections such as vector-borne rickettsioses, leptospirosis, and haemorrhagic fevers or lyssavirus-related illness, respectively“.  The authors also talk about how pet ownership, especially the increase in ownership of ‘exotic’ pets like reptiles is increasing people’s exposure to infections that previously they would never have been exposed to.

Socio-economic alterations – with an ever increasing global population there is an ever increasing demand for food, including meat.  It also means that as urban populations are expanding people are moving into previously uninhabited areas and so are being exposed to disease-causing agents that they had never been previously.

Political alterations – the authors talk about some countries with poorer veterinary surveillance or that have focal areas of zoonotic infections that previously were not having a global impact because they had strictly state-controlled economies but are now having a global impact because they have transitioned to allowing free  trade.  They also discuss the role that political disruption and upheaval can have on increasing the spread of zoonotic infections.

Scientific impacts – Part of the reason that we are recognising so many zoonotic infections is that we have got better at detecting them.  Infectious agents that we couldn’t have characterised decades ago can now be identified and classified.  Another scientific impact the authors mention is one that you will recognise if you are a regular reader of this blog: there have been many advances in medicine that allow us to live to an older age, but that have a negative impact on our immune system (for example, chemotherapy drugs can make us immunosuppressed; if you have an organ transplant you have to take immunosuppressing drugs, etc.)  This leaves a section of the population at a much higher risk of contracting any disease and so gives rise to some human infections with agents that would otherwise not normally infect humans.

Factors Associated with Pathogen Characteristics

The authors talk about how pathogens (disease causing organisms) that have a high genetic mutation rate (like flu viruses) can help them become zoonotic infections: in the authors’ words ” their enormous mutation rate is essentially a factory producing the species that are most potently pathogenic for humans

The authors also talk about how biodiversity can impact zoonotic disease transmission in this section (although, personally I’m not sure why it came into this section).  They talk about how sometimes wide diversity can reduce the spread of zoonotic agents because (if I am parsing this correctly) if there are many host animals that a vector (like a mosquito) can feed off there is less chance of it coming into contact with an animal that harbours the zoonotic agent – this is called the ‘dilution effect’.

Climate Change and Zoonotic Infection Resurgence

To quote from the paper: “Global warming is an ecological emergency, but its implications for human disease caused by infectious agents remains understudied“.  We do know some of the effects it could have – increases in temperature in previously colder countries leads to the spread of insects like mosquitoes – and the diseases they carry –  into those countries.  Climate change may also affect bird migration patterns and so may affect the exposure of birds to pathogens and also the exposure of us to them via the birds.

Finally the paper finishes with Projections for the Future. The authors point to 4 issues that “need urgent clarification and further attention“.

1) Recognition of the need for pre-emptive studies on the effects of massive or smaller developmental projects on local animal fauna and local zoonotic reservoirs

2) Recognition and enhancement of the health literacy of special populations that are at increased risk for the development of zoonotic infections (meaning that those patients on immunosuppressant drugs or who are immunosuppressed for other reasons should get more information about where they might encounter zoonotic infections and hw to avoid them.

3) Recognition of the major long-term burden induced by certain of these diseases with a chronic phase. There are some diseases that take a long time for any symptoms to show.  If a person has migrated from an area where the disease is relatively common to one where the disease is rare, the clinicians may be less likely to recognise the disease (or may recognise it at a later stage than if they were practicing in a country where the disease is common).  The authors recommend that clinicians “should be prepared to recognize the long history evolving in such patients and the extreme costs, mentioned in the introductory section, that will be passed on to the host countries”

4) Planning any intervention is difficult, for financial and scientific reasons. The burden of many of these diseases remains unrecognized… any zoonosis imposes a threat to the family as a unit—exposure is likely to be common for members of a household, particularly in agricultural settings, and animal loss (owing to the disease or state regulations for sick animals) may have a significant impact on the economy of the household, which is further worsened by the often observed inadequate access to appropriate medical treatment for the human patients themselves (imagine the scenario in any impoverished or conflict-active region of Africa or Asia). … ambitious eradication campaigns are not always feasible when all of the aforementioned issues have not been taken into account, and neither are successful elimination campaigns, as these may have temporary positive results but subsequent surveillance degeneration, leading to zoonotic resurgences, usually with some twists. (So basically we don’t really fully know the burden of most zoonotic diseases and rushing in there with eradication campaigns without considering all the other factors is not necessarily the best move.)

I think sometimes it can be really easy to think of zoonotic diseases as something one human gets from one animal, but this paper was a good reminder that these diseases can have a much broader impact.  It also had a useful discussion about why the number of zoonotic infections seemed to be increasing, but as it said (and as all papers say) there is still more work to be done in this area.

Image credit

All images were released under a creative commons licence (see links for details).  Thanks to Rugby471 for the dollar sign, to Wegmann for the tourist shot and to DROUET for the virus

Reference

 
Cascio A, Bosilkovski M, Rodriguez-Morales AJ, & Pappas G (2011). The socio-ecology of zoonotic infections. Clinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious Diseases, 17 (3), 336-42 PMID: 21175957

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More on Schmallenberg virus…

May 30, 2012

The Society for General Microbiology has released a nice, easy-to-read briefing on Schmallenberg virus which can be found here (pdf).  Plus they have also made available the Schmallenberg lecture I mentioned in this post

 

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Schmallenberg virus – what we know so far

April 2, 2012

Watching the research that surrounds the emergence of a novel virus is fascinating. I’m always amazed at how quickly scientists basically dissect the disease and the organism to find out what is going on.

Today’s post is going to look at Schmallenberg virus – a novel virus affecting livestock that was first identified only in November 2011.

The story actually begins before November 2011.  It’s thought that the virus first started affecting livestock in Europe in summer 2011: cattle in Germany and the Netherlands started to show a few non-specific signs of disease (fever, diarrhoea, a drop in milk production).   The animals generally got better again after a few days and herds were generally only affected for a few weeks.  Samples were collected and tests were run to find out what was going on but the tests ruled out known viruses and it remained a mystery…

… until November.  It was then that the virus was isolated by scientists who named it after the town, Schmallenberg, that the first positive sample came from.  (I’m not sure how happy residents of Schmallenberg will be to have a virus named after their town!)

Since its first identification scientists have learnt a lot:  SBV is very closely related to a subgroup of viruses in the Orthobunyavirus group. Other viruses in this subgroup are commonly transmitted from mammal to mammal by insects like midges and mosquitoes so it has been suggested that SBV may also be transmitted this way. This would fit in with the fact that the initial cases were seen in August and September – prime insect months.

The reason we (at least in the UK) started to hear of new cases at the beginning of 2012 is probably not because animals are still getting infected (in winter there are usually no midges or mosquitos around).  We are seeing the long term consequences of animals infected by the virus when they were in their early pregnancy.  Farmers are seeing an increase in the numbers of miscarriages and stillbirths of deformed young, especially in sheep, although cattle and goats have also been affected by the virus.

Since scientists first isolated SBV it has been grown in the lab and a very small number of cattle have been experimentally infected with it, resulting in a similar picture of non-specific symptoms as was seen in cattle in the summer of 2011.  There is still a lot of work to be done in this area – we don’t yet know if animals can pass the virus directly to each other and we don’t know what is going to happen in 2012.  Exposed animals may prove to have some immunity but what about those animals who were unexposed but are close to exposed ones?

SBV is currently not thought to be zoonotic: the European Centre for Disease Prevention and control states that  it is “unlikely that this virus will cause disease in humans, but it cannot be excluded at this stage“.  It actually must be quite hard to prove that a virus doesn’t cause disease in humans.  You can do cell culture work and see if the virus affects particular cell lines, but barring injecting a large number of people with the virus, you basically have to say well x number of people have been exposed and no one has caught any disease (and you would have greater confidence the larger x is).  (Well that’s how I understand it anyway – please correct me below if I am wrong.)

Countries across Europe are trying to get a handle on the disease and plan for the months when midges and mosquitoes will be around in 2012.  In the UK, as of 30th March 2012 it had been detected 235 farms, mostly sheep farms.  However the number of cattle herds affected may increase as those cattle infected in their pregnancy in late summer are now starting to calve.   SBV is not currently a notifiable disease (although Defra does ask farmers to notify their vets if they suspect it) but I don’t know if this will change as the months go on.

I think it’s amazing how much scientists have learnt in the space of about 9 months since vets first saw the signs of infected cattle and I’ll be keeping a close eye out for the next set of results to be published.

Places to go for more info:

Latest UK SBV situation

Information from Defra on the virus

Scenarios for the future spread of Schmallenberg virus  (Veterinary Record, 2012 170 245-246 doi: 10.1136/vr.e1598 – BEHIND A PAYWALL)

Information from the ECDC

ECDC Preliminary Risk Assessment 

 

Image:

Lamb picture made available by Evelyn Simak under a Creative Commons Attribution-Share Alike 2.0 licence

Cow picture made available by CRV Arnhem under a CC-BY 3.0 licence

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Sadly pet ownership comes with risks

March 13, 2012

Maryn McKenna over at SUPERBUG has got a post up discussing a recent paper (see below) that looked at 3 cases of (human) infection with Pasteurella multocida.  In all 3 cases it is thought that the patients involved caught the bacteria from nursing their sick pets.

Pasteurella multocida is a nasty species of bacteria and infection with it can very easily be fatal in humans.  Human cases are mostly associated with scratches and bites from cats and dogs (P. multocida can and does live happily in their mouths without causing any problems to them). However, in the cases published in the paper the transmission from animal to human seems to be effectively from mouth to mouth, rather than via injection through the skin as would happen with a bite.

It’s a very sad reminder that whilst pet ownership has many many benefits, we shouldn’t ignore the risks.

 

Paper Cited:

Myers EM, Ward SL, Myers JP. Life-threatening respiratory pasteurellosis associated with palliative pet care. Clin Infect Dis. 2012 Mar;54(6):e55-7. Epub 2012 Jan 11. DOI: 10.1093/cid/cir975 (May be behind paywall)

Images:

Photo by Adriano and released under a Creative Commons Attribution- Share Alike 3.0 Unported Licence

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“Pig” MRSA – are the pigs really to blame?

February 23, 2012

Photo by Keith Weller

There is a strain of MRSA (methicillin-resistant Staphylococcus aureus) that has been tracked passing from pigs to humans.  It was always thought that the MRSA initially came from the pigs, but new research published in mBio (open access) suggests that pigs might not be the original source. 

Instead it looks like the strain may have originated in humans but been methicillin-susceptible.  It then at some point passed into pigs where it picked up some antibiotic resistance genes from other bacteria before then going back into humans (especially farm workers and others who have close contact with pigs) as a more dangerous strain.

Unfortunately antibiotic resistance is one of the problems we face when bugs (in the sense of pathogens, rather than insects!) can so easily share and swap their genetic material.

One of the co-authors on the paper, Tara Smith has written an interesting post about it over at her blog, Aetiology which is well worth a read.  (If you’re interested in antibiotic resistance, public health and epidemiology her blog is definitely one to add to your RSS feed.)

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Darn it!

July 21, 2011

Not only is there a paper out discussing the characterisation of the latest E.coli bug (see posts here, here and here) but the use of badger culling to prevent bovine tuberculosis cases in cattle is also back in the news – all stuff I want to blog about but I MIGHT ACTUALLY HAVE SOME RESULTS!!! (only taken 9 months…) so I hope you’ll understand if posts on these topics are somewhat delayed!

Also – my blogroll is still out of date but thankfully those that have moved have got links on their old pages directing the reader to their new pages. 

I’ll post on twitter as usual when the next post is up (or you can subscribe/add the RSS feed).

*skips back to lab to check on experiment*

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An unusual case of orf

July 18, 2011

ResearchBlogging.org

Diseases don’t always behave exactly as we expect them too.  Sometimes, even when we think we’ve worked out most things about them, they can surprise us.

A case study published in Dermatology Online Journal – Orf parapoxvirus infection from a cat scratch by J Frandsen et al (see below for full ref) – is a nice example of this.

A Bit of Background

Electronmicrograph of orf virus

Orf (AKA ‘contagious pustular dermatitis’ or ‘ecythema contagiosum’)  is caused by a parapoxvirus infection.  (Parapoxviruses are double-stranded DNA viruses and other diseases caused by these viruses include bovine papular stomatitis and pseudocowpox).  The orf virus is found across the world and is carried by sheep and goats.  It is also zoonotic.

In sheep and goats the virus can cause disease at any time but generally causes the most problems in and just after the lambing season.  In infected animals it manifests as pustular, scabby lesions.  These scabs are full of virus.  A new animal becomes infected if it has damaged skin that comes into contact with the virus, usually via direct contact with an infected animal. 

We can become infected in exactly the same way and it is a known risk during the lambing season.  Luckily orf infection is generally self-limiting unless we/the animal are immunocompromised for some reason (e.g. already ill/taking immunosuppressant drugs etc.)

Sheep with orf scabs

However, transmission doesn’t always have to be via direct contact.  Transmission of the virus by fomites has also been reported including infection after contact with sheep fences or burrs in the sheep’s wool.

What’s interesting about this case report is that the sheep host is much further removed from the human case.

The Case Report

The authors of the paper report the case of a woman who presented herself to her ‘primary care physician’ (I’m guessing that’s the equivalent to my GP unless anyone else can tell me any differently) with an ulcerating blister in a region where she had been scratched by a stray kitten 4 weeks earlier.  She reported no contact with any sheep or goats and had not been in any fields where they were grazed but she did live near farmland with sheep on it.  She was treated with antibiotics but the lesion just got worse.

After being referred to specialist dermatologists she had a skin biopsy.  Under the microscope this biopsy was seen to have features that are characteristic of parapoxvirus infections – this included eosinophilic (pink staining) cytoplasmic (imagining a cell as a fried egg: in the egg white) inclusions for any budding histopathologists out there.  There were other differential diagnoses that could also fit this pattern, including milkers nodules, but the authors state that:

“Because milker’s nodules are smaller and less likely to ulcerate than orf, we assume our patient had orf “

The authors do point out that they couldn’t identify the specific viral type, however, what they had learnt from the biopsy was enough to allow them to prescribe topical treatment for the woman and the lesion healed up in 10 weeks.

What this means…

Now we can’t be totally sure that this case was caused by the orf virus but if it was that means that the kitten had presumably been wandering around a sheep farm, picked up the virus on its claws (possibly from scab material on the ground?) then trotted away from the farm and towards where this woman found it.  When it scratched the woman it effectively inoculated her with the virus and that is how it was able to get in. 

I would suspect that (prior to this case report at least) if you were a medic presented with this case, when a woman reports absolutely no contact with sheep, sheep pasture etc. that would move orf quite far down your differential diagnosis list.  This case reminds us that zoonotic diseases are not always transmitted the way we expect. 

They certainly keep medics and scientists on their toes!

Lambie!

Images

With thanks to GrahamColm for the electron micrograph and Dnatheist for the sheep with orf images, both of which were licensed under Creative Commons Attribution-Share Alike unported 3.0 licence and with thanks to Evelyn Simak for the gorgeous photo of the lamb, licenced under Creative Commons Attribution-ShareAlike 2.0 generic licence.

Further information

Orf Infection in Sheep leaflet from the Moredun Research Institute

Information from the Health Protection Agency

Frandsen J, Enslow M, & Bowen AR (2011). Orf parapoxvirus infection from a cat scratch. Dermatology online journal, 17 (4) PMID: 21549084