Archive for June, 2012
Everywhere we look we are beset by the scourge of Salmonella. It turns up in bird feeders (Alley et al 2002), home aquariums (Levings et al 2006), and most recently in playground sand (Staff et al 2012). While Salmonella infections have been commonly associated with reptiles all animals should be considered carriers of Salmonella. I recall a case of diarrhoea in a kangaroo joey that was being hand raised. The carer, concerned for his welfare, took him to bed with her each night to keep him warm. Oddly enough the carer then developed the same diarrhoea as the kangaroo.
The US reports 40,000 human cases of salmonellosis each year (http://www.cdc.gov/nczved/divisions/dfbmd/diseases/salmonellosis/#how_common). Who knows how many unknown cases of salmonellosis there are? After all how many times have you submitted your faeces for bacterial culture when you had diarrhoea?
The thing is that most of these cases can be easily prevented. Salmonella really doesn’t like soap. With a bit of common sense (stop sleeping with your patients) and more attention to personal hygiene most of us should remain diarrhoea free. All it requires is to wash your hands with soap and water for at least 20 seconds (that’s equivalent to singing the Happy Birthday song twice) each time you handle an animal, clean the cat box, fish tank, etc and certainly before eating, preparing food or smoking. Actually don’t worry about washing before smoking. If, in this day and age, you’re still stupid enough to be smoking you probably deserve everything you get. Consult http://www.cdc.gov/features/handwashing/ for those who are hand washing challenged.
Dr. F. Bunny
Alley, M.R., J.H. Connolly, S.G. Fenwick, G.F. Mackereth, M.J. Leyland, L.E. Rogers, M. Haycock, C. Nicol, and C.E. Reed. 2002. An epidemic of salmonellosis caused by Salmonella Typhimurium DT160 in wild birds and humans in New Zealand. New Zealand Veterinary Journal 50:170-176.
Levings, R.S., D. Lightfoot, R.M. Hall, and S.P. Djordjevic. 2006. Aquariums as reservoirs for multidrug-resistant Salmonella paratyphi B. Emerging Infectious Diseases 12:507-510.
Staff, M., J. Musto, G. Hogg, M. Janssen, and K. Rose. 2012. Salmonellosis outbreak traced to playground sand, Australia, 2007-2009. Emerging Infectious Diseases 18:1159-1161.
Let us say, just for a moment, that God exists. That leads us to the difficult problem of religion, or rather, religions. Presumably the devotees of each faith believe theirs is the one true religion. In fact they may believe it so fervently that they are prepared to kill or die for that belief. But how can they know that they are right? Best case scenario: all religions are false, except one. Worst case scenario: they are all wrong.
If we assume that one religion is the real one, how do we know which one that is? Presumably Christians believe they are right because the Bible says so. But the Muslims have the Koran and the Jews have the Torah. Surely there cannot be more than one correct holy book? And what of the Christians? There are Catholics, Protestants, Methodists, Anglicans, Jehovah’s Witnesses and who knows how many others. How can they all read the same book, be provided with the same information, but come to conclusions different enough to make them want to start their own unique true religion, and reject the other false ones?
So, here is my dilemma. As a non-religious person how do I know which religion to choose, as I want to choose the right one, and there appears to be a similar lack of evidence supporting all of them? What if I make an honest mistake and choose the wrong one? Do I burn for all eternity? What of people living in the jungles, who haven’t heard of any of these religions? Do they burn solely because of their isolation?
A similar situation exists in medicine. Whenever a disease pops up for which there is no satisfactory cure a huge range of therapies appear, some conventional and some alternative, but all with the same characteristics: a lack of hard evidence proving that they work. Where a disease has a definite cure and there is evidence that the cure works, penicillin in the case of scarlet fever for example, that treatment dominates and the others disappear. I wonder if the same cannot be said of religion. Could there be so many religions because none of them are right?
Dr. F. Bunny
There are only 12 of you (Victorian brush-tailed rock wallabies) left in the wild in Gippsland, and your friends in the Grampians went extinct in 1999. That’s no good.
What’s that? Some people reintroduced some captive bred wallabies there a few years ago. Great. How did it go?
That’s a shame. They are almost all dead. Why is that?
They didn’t release enough of them because the geneticists would only allow Victorian brush-tailed rock wallabies to go out. But aren’t you genetically different from the New South Wales rock wallabies?
Oh, they may be genetically different but look exactly the same, and you would be more than happy to breed with them given half the chance. It must be a bummer to be so endangered, no one to talk to and no chance of filling your ecological niche. Is there anything we can do to help?
I see. Release a ton of wallabies from New South Wales because it’s surely better to have some wallabies hopping about the bush doing their thing than none at all. I know you’ve never been a racist and we shouldn’t be either. Sound words of wisdom, Skip. After all any endangered species is no use to anyone in captivity and we all know how tough it is trying to make a living in the wild. You need a lot of animals if enough are to survive and establish permanent colonies.
No worries, Skip. I’ll pass the message on and hope for the best. Good luck to you and your friends. I suspect you’ll need it.
And Sonny’s trapped in the ravine? Okay, I’ll let ranger headquarters know.
Dr. F. Bunny
I sometimes think there are good reasons why certain species are endangered. I am sure there are plenty of species who were minding their own business and doing pretty well for themselves until we entered the picture and wiped them out. The passenger pigeon springs to mind. However, there are others that look destined to become extinct whether we help them along or not. Nature seems to be telling them (and us) that their time is up. They had their moment of fame and now it’s time to step aside. The cheetah seems to be one of these. No matter what you do to help them they just seem destined to go extinct. Cheetahs are so inbred that they will accept skin grafts from unrelated individuals. Vaccines given to domestic cats to protect them from cat flu actually cause the disease in cheetahs. Normally mild infections, like ringworm, run rampant in cheetahs. Even the animal kingdom seems to be against them with lions doing everything they can to wipe them out by stealing their food and killing their cubs.
Given the limited resources that are available for endangered species programs and the fact that we cannot save them all, it would be logical to expect that those species that have recovery programs got there through a rigorous process of scientific examination exploring the pros and cons of attempting to save them as opposed to leaving them to die out. The chief criterion for commitment should surely hinge upon the program’s chance of success. Unfortunately nothing could be further from the truth. Species get recovery programs for three reasons: 1) someone powerful and influential in a zoo or related institution takes a liking to them and wants to make an effort to save them, 2) someone affluent takes a liking to them and is prepared to throw a heap of cash at a recovery effort, 3) they are cute. The final reason must surely explain all the money being spent on cheetahs and giant pandas. This also helps to explain why many of the species with recovery programs do so poorly, such as the orange-bellied parrot which is worse off now than when its program started over 15 years ago.
Dr. F. Bunny
“Just one question, what is Immobilo and how does it work?”
“Actually that’s two questions.”
“He’s bright. I like that.” (Get Smart, Episode 8, Our Man in Leotards).
So, what is vaccination, and how does it work?
All life forms, from humans down to earthworms, have some kind of internal defence system used to ward off unwanted invaders such as bacteria, viruses, fungi and parasites. In vertebrates these are the white blood cells. There are two main types. One group produces antibodies, while the others wander around killing trespassers directly. In most cases antibodies don’t kill invaders by themselves but incapacitate them in such a way that the killer cells have an easier time of it.
The thing about the antibody producing cells is that they have memories, quite long memories in some cases. If the same enemy pops up subsequent to an earlier defeat they move into action much faster and produce antibodies earlier than before. In this way they get on top of the infection before the infection gets on top of them. It is this memory that is exploited by vaccination.
All invaders have proteins on their surface that the white blood cells recognise as being foreign and not belonging in the body. When they detect these proteins they swing into action. There are two types of vaccines. Killed vaccines contain the proteins but the agent is dead. Modified live vaccines also contain the proteins but the agent is still alive. It has been rendered incapable of causing disease but, because it is alive, provokes a more vigorous longer lasting response
Once the vaccine is administered antibodies are produced and the white blood cell memory kicks in. In that way if they encounter the real disease in the future they swing into action earlier and prevent disease from happening. This is why vaccines work to prevent disease but are not of much use once the disease has taken hold.
Unfortunately white blood cell memory is very specific and will only recognise one particular version of a disease causing agent. That is why we need a different flu vaccine each year. Flu viruses are covered in one of 16 different proteins called haemagglutinins (H) in combination with one of nine different proteins called neuraminidases (N), hence H1N1 (swine flu) or H5N1 (bird flu). Unfortunately the cells that recognise H1N1 ignore H5N1 or any of the other flu combinations. The discovery of a protein present on all flu viruses may finally lead to the development of a universal flu vaccine that will protect against all flu viruses. The same holds for cold viruses. Every time we catch cold we are infected with a brand new virus the body has not seen before. When our family catches cold and we avoid it this may be because we have already contracted that virus at a prior point.
Unfortunately vaccines are not 100% effective, and can occasionally cause side effects. As Monty Python’s “Life of Brian” tells us, “We’re all individuals”. Consequently we all react differently, with some people achieving better protection than others. Getting vaccinated while we are sick will decrease its effectiveness because our white blood cells are otherwise occupied. People with compromised immune systems will also not respond well to vaccination. Unfortunately some people have adverse reactions to vaccines. These are rare and usually mild but can occasionally be quite severe. It doesn’t happen often and, as vaccine technology improves, will continue to become rarer, but that is no consolation for the people who are affected.
It is these sorts of events that help fuel a lot of the anti-vaccine hysteria. Presumably these people are genuinely concerned about the negative effects of vaccination and whether or not they actually work.
It has been said that improved hygiene and nutrition are responsible for the decline in diseases, not vaccination. Like any war victory comes from employing multiple strategies. Vaccination is just one of those strategies. When used in concert with better food and sanitation it can play a major role in decreasing the incidence of diseases, but it can also be very effective on its own. As an example, in the early 1990s there were about four million chicken pox cases annually in the US, a country with good hygiene and nutrition. After the introduction of a chicken pox vaccine in 1995 the incidence of chicken pox had dropped by 85% by 2004 (http://www.historyofvaccines.org/content/articles/top-20-questions-about-vaccination). Confusingly anti-vaccinationists trot out figures showing an increase in the incidence of certain diseases post-vaccination. When confronted with contradicting tables of figures it is very difficult to make an informed decision. Who do you believe?
Unfortunately the anti-vaccinationists haven’t done themselves any favours by supporting various bizarre conspiracy theories. One of my favourites revolves around the plane crash in Smolensk that killed the Polish president two years ago. Apparently the plane was shot down because Poland was the only country not to buy H1N1 vaccines (http://www.bing.com/videos/search?q=polish+plane+crash+conspiracy&docid=4880706944237728&mid=42F5E38BA6E30AFB445942F5E38BA6E30AFB4459&view=detail&FORM=VIRE4). Even though smallpox has been officially eradicated from the world we are still getting reports that it is alive and well and causing disease in India (http://vactruth.com/2011/03/28/news-of-smallpox-outbreak-in-india-raises-fear/). The exciting thing is that, with the assistance of vaccination, a second disease has now been made extinct. Rinderpest, a scourge of cattle farmers for thousands of years, is no more. Perhaps the greatest blow to anti-vaccination credibility was the manipulation of evidence by a physician in an attempt to show that vaccination caused autism. His paper was withdrawn from the medical journal in which it was published and he was struck off the Medical Register for falsifying results (http://en.wikipedia.org/wiki/MMR_vaccine_controversy).
I will admit to being biased, because I am medically trained, but I have seen first-hand evidence that vaccinated animals mount an immune response and resist disease challenge. Given the rather dubious information put out by the anti-vaccinationists I prefer to be on the side supported by credible evidence and will continue to vaccinate myself, my family and the animals in my care. Not to do so would be irresponsible in my view.
Dr. F. Bunny
How disease occurs is an interesting and extremely complex subject. For pandemics to take off multiple factors need to take place. To better understand these interactions I can recommend a board game called “Pandemic”. Uniquely, players battle not against each other but against four diseases raging across the globe. They must find a cure and wipe out the diseases before they extinguish humanity’s light. Conversely, if you prefer your medicine on the dark-side there is an interesting phone app called “Plague”. In this game you take the part of the disease. You must mutate your organism to enhance its transmission, resistance and lethality. Both games provide insight into how difficult it is for a disease outbreak to start and, once started, how hard it can be to stop it in its tracks.
A recent literature survey identified 1407 recognised species of human pathogen, 58% of which are zoonotic i.e. transmissible from animals to people. Of these 177 are regarded as emerging or re-emerging, with 73% of these being zoonotic (Woolhouse and Gowtage-Sequeria 2005). At first glance bats appear to be over represented as reservoirs of disease, being maintenance hosts for potentially fatal viruses like Australian Bat Lyssavirus, Hendra virus, Nipah virus, and Menangle virus. Bats, not civets, may also be the natural reservoir for SARS and the ever popular Ebola virus (not great apes as was initially thought). So, what is it about bats that make them such popular hosts for some of our scariest diseases?
Bats, in fact, are not over represented as ungulates (cattle, sheep, goats, etc) support the majority of the world’s zoonoses (over 250) and emerging diseases (over 50). Bats harbor less than 2% of human pathogens (Dobson 2005). Unfortunately the ones they do carry are associated with high human mortality rates, making them of much more interest to the media.
It is important to remember that there are a lot of bats, approximately 1240 different species. This represents more than 20% of all known mammal species (second only to the rodents). Bats are also the only mammal that can fly. Therefore, they have more opportunity to contact animals at different locations, enhancing opportunities for spread and transmission. Bats live in large groups, which also increases the potential for disease spread. Just look at how quickly the common cold rips through human populations.
One interesting theory postulates that there are good viruses as well as bad (this is starting to sound like an episode of Red Dwarf – http://en.wikipedia.org/wiki/Quarantine_(Red_Dwarf)). Hendra virus causes no disease in bats but does stimulate the bat’s innate immunity. This may help to protect it from other disease agents. Hendra virus normally persists at low levels in bat colonies. However, under conditions of stress, such as habitat destruction or potential predation, viral load and, therefore, viral shedding increases. As the virus is particularly deadly to other species, such as horses and humans, its release could act like a protective umbrella for the colony (Wang et al 2011).
Most of these disease agents evolved with bats over a long period of time and cause them no trouble. As habitat continues to be cleared, these viruses will contact new hosts (i.e. humans) with no prior immunological knowledge of them with ever increasing frequency. Viruses, like the rest of us, don’t enjoy being kicked out of their comfortable homes and forced to live somewhere new and strange. They tend to get a bit grumpy and anti-social and attempt to demolish their new house. Unfortunately for them, as the house is destroyed, so are they.
Our ability to diagnose diseases is always improving. Incredibly a recent paper reported that 57.2% of fatal encephalitis cases in Australia between 1993 and 2006 were undiagnosed (Huppatz et al 2009). Some of these cases could have been caused by previously unrecognised viruses. It is also a case of the more you look the more you find. Now that our antennae are up we will be searching harder than ever before and are almost certain to turn up new viruses (in fact a relative of the Ebola virus popped up recently in bats in Spain (Negredo et al 2011)).
This should not, however, be interpreted as open season on bats. Bats perform an incredibly important function as seed dispersers, plant pollinators and consumers of vast quantities of insects, many of which harm agricultural crops (Wibbelt et al 2010). Their demise would be catastrophic for agriculture and the planet as a whole. As we expand into new habitats novel diseases will continue to pop up, not just in bats, but likely in a range of species. We need to be aware of the risks, take steps to mitigate them and, in the words of John Howard, “be alert but not alarmed.”
Dr. F. Bunny
If, like me, you want to keep abreast of the situation and have all the latest disease information at your fingertips there are a few excellent websites worth consulting. The Centers of Disease Control and Prevention site contains a wealth of information about every disease you can think of, and probably quite a few you can’t: http://www.cdc.gov/. ProMED provide twice daily alerts about new diseases as they break. They cover not just human diseases but animal and plant ones too. Truly a hypochondriac’s delight: http://www.promedmail.org/. And if all that isn’t enough to make you live inside a plastic bubble for the rest of your life download the HealthMap app to your phone for disease alerts near you: http://www.healthmap.org/en/.
Dobson A.P. 2005. What links bats to emerging infectious diseases? Science 310:628-629.
Huppatz C., Kelly P.M., Levi C., Dalton C., Williams D. and Durrheim DN. 2009. Encephalitis in Australia, 1979-2006: trends and aetiologies. Communicable Diseases Intelligence 33:192-197.
Negredo A., Palacios G., Vazquez-Moron S., Gonzalez F., Dopazo H., Molero F., Juste J., Quetglas J., Savji N., de la Cruz Martinez M., Herrera J.E., Pizarro M., Hutchison S.K., Echevarria J.E., Lipkin W.I. and Tenorio A. 2011. Discovery of an ebola-like filovirus in Europe. PLoS Pathogens 7:10:e1002304.
Wang L.F., Walker P.J. and Poon L.L.M. 2011. Mass extinctions, biodiversity and mitochondrial function: are bats “special” as reservoirs for emerging viruses? Current Opinion in Virology 1:649-657.
Wibbelt G., Moore M.S., Schountz T. and Voigt C.C. 2010. Emerging diseases in Chiroptera: why bats? Biology Letters doi:101098/rsbl.2010.0267.
Woolhouse M.E.J. and Gowtage-Sequeria S. 2005. Host range and emerging and reemerging pathogens. Emerging Infectious Diseases 11:1842-1847.
I can see this post is going to have more sequels than Rocky. If it’s not enough that rainbow lorikeets are dying in droves around Melbourne because people are feeding them, Blue Cross Aged Care Facilities (http://www.bluecross.com.au/bluecross-tvcs) are running an ad showing an aged gentleman feeding seed to rainbow lorikeets! He seems happy and so are the birds. Why not? With all those sunflower seeds in the mix it’s like being fed a family sized bar of chocolate each day.
Dr. F. Bunny