Infectious Diseases II

Control, Elimination, Eradication, Extinction.

In this chapter I’d like to look at the control, elimination, eradication and extinction of infectious diseases. Again, let’s look at some definitions here. By control we mean the reduction of the prevalence, that is the number of cases at any one time, incidents, the number of new cases over a period of time, to locally acceptable levels which is usually interpreted to indicate no longer a public health priority. Intervention however is still required. Elimination is the reduction of disease to zero and or infection to zero. The intervention, however, may still be required. An eradication is the permanent reduction of global, we’re now talking about the whole world, incidence of disease to zero with the organism not present in nature. No intervention at this point is required. And now let’s take a look at some of these terms as they play themselves out. The criteria for eradication which is the area I’m going to focus on in a moment is that humans are the only reservoir and there are no non-human vectors. Now we’re talking about eradication in people.The absence of a carrier state. That means that people don’t carry the organism even though they’re not sick. The feasibility of the intervention, is it effective? Is it acceptable? Is it affordable? Do we have ways to monitor whether this infection is present in the community, surveillance? Are people concerned and fearful enough that they will buy into these programs and does government have a strong enough commitment to try to eradicate a condition? Now infectious diseases that have been eradicated, there is only one and that is smallpox. And this was done primarily through a vaccine. Other infections that have been pretty much eliminated from many countries are guinea worm, which is only now found in some parts of sub-Saharan Africa, neonatal tetanus or the tetanus of the newborn. Again, vaccines here. There are still some cases but not very many even though the tetanus bacilli exists in the ground around us. Polio, we’re very close to eradicating this through vaccine but there are still cases in some parts of Africa and South Asia. Diphtheria, these have come way down, as has leprosy. The…but again, smallpox is the only human disease that we have been able to eradicate. There is a disease in cattle called rinderpest that has been eradicated, but this is the only one for humans. This is what smallpox looked like. It was a terrible disease. This child has lesions all over the body, it sometimes would in addition to causing a lot of deaths, it also caused blindness, and many other complications. This was a typical picture of a smallpox case. I’m now going to talk about the vaccine that was developed to deal with this. It was noted by Edward Jenner, a practitioner in rural England, that cow…that women who milked cows, cowgirls I guess you’d call them, did not get smallpox and he noted that on their hand was a lesion that was gotten from the cows that they worked with which was cowpox. He reckoned that if it protected these  women and he took this from one woman who milked cows, Sarah Nelmes, that maybe this would protect people against smallpox. And in fact, he tried out the first vaccination was in 1796. Now prior to this, people had taken the serum, the lymph from the smallpox lesion of very mild cases and gave it to people hoping they would also develop mild disease. Sometimes it worked, sometimes it didn’t. Now despite the fact that this was shown to be extremely effective, there was a lot of resistance against this. This is a picture from a British publication, a humor publication called Punch and here is Jenner in the middle and people have cows growing out of their arms, their back sides, their face and so on. People figuring if they got the cowpox they might even turn into cows. Now, smallpox actually had eradication potential. What was that? Well, going back to those earlier criteria, there was universal fear, there was no animal reservoir, people were the only ones who had this disease. Nobody was a carrier, there was lifelong immunity after a single episode and a characteristic rash. There was no transmission from subclinical cases, as there were none. And we had a very, very effective heat stable ‘ (We didn’t need a refrigerator) vaccine and we had the development of a needle called the bifurcated needle which allowed us to easily transmit the vaccine to an individual. We also developed a very effective way of searching and containing this because smallpox moved relatively slowly through populations, once we found a case we could immunize around it so the case would be the orange circle there, we could then immunize around it, that would be the purple, and then we could also immunize the contacts of the contacts by taking these circles and moving out in this ring vaccination area we could reduce and eliminate smallpox from areas without having to immunize absolutely everybody in the population. We also minimize adverse events and we found that this vaccine was highly efficacious in preventing disease. The last case of…major case of variola minor occurred in Bangladesh in a young girl, Rahima Banu in 1976 and in 1977 the last case of variola minor appeared in Somalia in Ali Maow Maalin who just died recently. He devoted much of his life to also dealing with other disease elimination and eradication programs. The next disease I’d like to address is polio. Here are some children, we don’t see this very much anymore, because polio has almost been eradicated and has been eliminated from almost every country of the world. These children would develop paralysis, primarily in their legs, and in some places they would have to be beggars unless there was some way of looking after these children. In certain cases the disease affected the bulbar region of the brain and people would have to be on respirators, sometimes for lifetime because they could no longer breathe on their own. But with the polio eradication campaign globally we are down to now hundreds of cases rather than hundreds of thousands of cases. Getting those last few cases of course are extremely difficult so we can not say that this disease has been eradicated but it has been eliminated from probably 98% of the world. This is a very inexpensive, very efficacious vaccine. This is the oral vaccine. There’s also IPV which is an injectable vaccine but it is more expensive. If you look at the polio incidence by month, just in a four year period between 1994-98 in India, you can see that it was very high in 1994, peaked to over 110,000 cases, then came down in 1995 and at the end of ’95 and the beginning of ’96 they had national immunization days where they gave the vaccine to every child under a certain year. I think under five years of age. This was repeated again at the end of ’96 and ’97 and again at the end of ’97 and ’98 so that the number of cases came down dramatically. In fact, India has now been declared polio free and it has been eliminated officially from this country, which is a huge undertaking given the population of 1.2 billion There are other infectious diseases that have decreased dramatically in incidence, that is the number of new cases, with a significant reduction in mortality and morbidity. Measles is one of these which is a major killer, was a major killer of children. Rheumatic fever which affected the heart, hepatitis B which sometimes leads to liver cancer, and also peptic ulcer and helicobacter where treatment of these conditions with blockers of stomach acid and antibiotics has greatly reduced the incidence of these conditions. Here’s a child with neonatal tetanus, a condition which we rarely see today and that’s because now mothers are immunized against tetanus and they pass this immunity on to their child until that child can be immunized themselves. And lastly here’s a picture of measles which has been up until recently a major killer of children in low and middle income countries. So what I’ve tried to do in this last chapter is to review for you control, the terms control, elimination and eradication. I haven’t dealt with extinction because extinction means that there is no presence of this organism anywhere in the world and most of these organisms exist still in some laboratories. I’ve shown you eradication as it occurred with smallpox and the efforts that are going forward with polio. And lastly we’ve looked at a couple of diseases that have come down dramatically in their incidence and prevalence in the world.

Pedro Pereira Leite

Researcher and professor. He had his PhD. on museology in 2011, with the title “Muss-amb-ike Homeland: The commitment on musicological process”, that was published in 2011. In 2012 he finishes a Post-PhD Research on "Biographical Glances: The intersubjectivity poetry on museology, at Lusófona University (Lisbon). Presently he is working in his Post PhD. Research about: “Global Heritages" with the aims to build a network on local cognizance and memory manager has a tool to build the will of action in 3 different communities, linked by past communed heritages.” He works at CES. He participates on different Research network, presented papers in national and international conferences, and had published books on research subjects.

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