Posts Tagged Pandemic

Some Like It Hot

As I emerged from the aerobridge into the Manila terminal I noticed a woman pointing a weird device at me. It was a thermal camera, a gizmo used to measure skin temperature. High temperature areas show up yellow or red while low temperature areas are blue or purple. Given the current paranoia about things like bird flu and SARS this camera was being used to screen passengers in case someone had a fever, which could be indicative of an infection with one of these diseases. If you read the literature put out by the company that produces it (http://www.flir.com/cs/apac/en/view/?id=42362) they would have you believe that this is an effective screening process. But is it?

Thermal cameras have been used in veterinary medicine to detect lameness and abscesses by the heat they generate. You will no doubt have sprained something at some point and noticed how warm the area became, because of the inflammatory process. This is different to the central fever that is generated by infectious agents. According to the company’s literature the temperature in the corner of the eye most closely approximates core body temperature. The literature also states that “glass and plastic do not transmit infrared radiation, so people need to remove their glasses in order to be examined.” That’s me slipped through the net. The recommendation is also to scan individual passengers at a distance of 1 to 1.6 metres so that the face fills the screen. How this is possible for the mass of humanity streaming off the plane, where some people are looking ahead, others are looking to the side and still others are looking at the ground, is beyond me. However, this is more an operational fault than a fault with the camera per se.

A recent study attempted to objectively evaluate the effectiveness of thermal cameras in detecting fever. In this study all subjects that wore them removed their glasses and stood still in front of the device for two to three seconds, very different to the moving people at the airport. Using this method the thermal camera had a 90% sensitivity (10% of the people who had a fever were not detected) and an 80% specificity (20% of the people who were detected as having a fever did not actually have one) (Nguyen et al 2010). These figures were deemed to be acceptable even though it meant that some people escaped the surveillance net while others would be falsely detained. Still no system is 100% fool-proof.

What also puzzles me is what the authorities would have done if they had registered a positive. Presumably that person would have been asked to stand aside for further investigation, but what of the other passengers? Would all the previous passengers, who had by now dispersed through the terminal, be rounded up? Would all the passengers yet to emerge from the plane be detained? Surely if one person had a fever then all the passengers and crew would need to be regarded as infected, as we had all been breathing the same air for the past however many hours? Veterinary medicine is much more straightforward and logical. Any animals shipped overseas need to have a defined set of vaccinations beforehand (e.g. rabies if coming from a rabies endemic country) and they enter a period of isolation after arrival at their destination. If they are healthy at the end of this quarantine period they are free to go. This is of course completely impractical for people, who like to jet-set around the world on a daily basis. However, it certainly does enhance the potential for diseases to spread rapidly around the world as we saw with SARS, which travelled at the speed of flight from Asia to Canada.

The other problem with thermal imaging is that it only detects infected people who have a fever. Many diseases, such as bird flu, have an incubation period of several days during which the infected person displays no clinical signs but is still potentially infective.

I don’t know what the solution to averting a pandemic is, possibly a combination of individual country surveillance of people and animals coupled with vaccination. Infrared thermography has a potential role to play but only if used properly and not in the haphazard manner I saw in Manila. Unfortunately this would add to passenger inconvenience, which would, however, be a small price to pay if it might avert or mitigate a pandemic.

Dr. F. Bunny

Reference

Nguyen, A.V., N.J. Cohen, H. Lipman, C.M. Brown, N.A. Molinari, W.L. Jackson, H. Kirking, P. Szymanowski, T.W. Wilson, B.A. Salhi, R.R. Roberts, D.W. Stryker, and D.B. Fishbein. 2010. Comparison of 3 infrared thermal detection systems and self-report for mass fever screening. Emerging Infectious Diseases 16: 1710-1717.

 

 

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Vaccination 101

“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.

 

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