Monday, October 3, 2011

Germlines #6: Phylogeny of Place and Plague

This week on the Germlines, I look at the geographic lines of distinction in the molecular epidemiology of Yersinia pestis in one of the world's hotspots of plague activity: Madagascar. The podcast is based on a paper published in this month's in PLoS Neglected Tropical Diseases. It is entitled,Phylogeography and molecular epidemiology of Yersinia pestis in Madagascar.

Listen here

17 comments:

  1. In listening to this podcast and reading the article on the molecular epidemiology of Yersinia Pestis, I'm not sure if there's a clear answer as to why for over 60 years, the plague had nearly disappeared and now suddenly re-emerging. According to the article, there are definite genetic similarities in the Yersinia Pestis strains over the years, seen in the SNPs and VNTRs. Certainly the black rats spread the disease locally, but for the distance travel, transportation methods, such as the steam ships and by railroad as rural areas became more industrialized over the years contributed to the distant spread. With this trend, in the future (or currently), will the rats board cargo planes and spread the plague to other parts of the world?

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  2. Gul Bahtiyar said;

    According to reports on the Internet, death toll from plague is rising. As of April 2011 the number of deaths from pneumonic plague is at least 260 people. (R. Herriman, examiner.com). It is not known why plague is emerging again after being disappeared for many years. What is different today that transmission of Y. Pestis from rats and humans causing an outbreak and cause death?

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  3. After listening to the podcast I found it very interesting that Yersenia pestis has reemerged as an epidemic after so many years, and mostly because of the phylogeography in Madasgascar.  I am just wondering that if Yersenia pestis can be mapped through genetic mapping and human movment, and can also be traced to the local black rat, what is being done to contain this organism to prevent any future infections? I read that UNICEF has started a disinfection campaign in Madasgcar targeting this epidemic, which is a wonderful idea, but that does not seem to be enough. If it was found that the black rat carries this organism then it seems that more focus should be on clearing these rodents from the towns, and also monitoring the amount of movement from each town that contains a large number of these rodents.

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  4. The podcast referred to how through genetic mapping, investigators were able to trace isolates of Yersinia back to different locations in Madagascar, how there was a reintroduction of strains from the highlands to Mahajanga, and how that reintroduction is related to the natural cycle between the black rat, flea, and host. Reading about the outbreak that took place in Surat in 1994, I wonder how the natural cycle and human movement were related to the outbreak of pneumonic plague, a rarer version than bubonic plague, in the region. Also, because of the panic that erupted because of the outbreak, I wonder what protocols were put in place to handle future situations and what other countries have done from witnessing the chaos.

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  5. The ability to determine plague transmission via genetic mapping of various isolates of Yersinia Pestis through different places and for over 60 years is truly amazing. It is fascinating how genetic differences are correlated with geographic distances, and how they were able to determine the strains in Mahajanga came from the central highlands from this mapping procedure. I wonder what other infectious diseases are currently being genetically profiled, and I wonder what the future of molecular biology could hold for the field.

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  6. I find the way in which this disease is transmitted to be very interesting. I wonder why the U.S. contributes so few cases of plague to the global total when it is the country with the largest enzootic foci. But even more so I wonder if the number of cases here could be underreported. According to the CDC, “The drugs of choice are streptomycin or gentamycin, but a number of other antibiotics are also effective.” So I wonder if it is possible that people go to the doctor before the symptom of swollen bubos appears, the doctor prescribes an antibiotic, patient feels better and no one ever suspects plague. Is that possible, or is there really no mistaking the plague?

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  7. I agree with Anika. While reading I thought Is it that difficult to keep the rodents off of trains and boats? According to the WHO Madagascar has been taking preventive measures by trying to cut down the rodent population. They do this by: periodic bush clearing, removal of potential rat habitats in houses, promotion of rat-proofing devices, incineration of dead rats, management of household waste and periodic rat capture for laboratory analysis. But they also note the importance of education in getting the cooperation of the people.

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  8. And the source...
    http://www.who.int/csr/resources/publications/WHO_HSE_EPR_2008_3w.pdf
    It has some pretty interesting stuff.

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  9. I agree with Jennifer in how incredible it is to determine plague transmission by the genetic mapping of Yersinia Pestis through different places. Genetic mapping is a technology that has made a great difference in the control of infectious diseases and it must be a very powerful tool, especially when dealing with a new virus that may be invisible to other medical tests. I can only imagine that it will greatly help public health efforts, control of various diseases, and enable much faster responses to deadly outbreaks.

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  10. Thanks Nicole for providing the info about WHO meeting on prevention and control of plague which was held in Madagascar in 2006. Up until reading this document I was not aware how widely spread plague is and and considered as epidemiological thread to many countries in the world. It also summaries the wide variety of antibiotic choice but limited use of vaccines. Apparently vaccines confer long-lasting protection against bubonic plague but they do not protect against pneumonic plague.

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  11. In response to anonymous:

    I do not think that a doctor prescribing antibiotics for general fever would treat a bona fide case of yersinia pestis plague. Often physicians prescribe azithromycin for upper respiratory tract infections or nonspecific fever. But azithromycin does not have activity against yersinia pestis. Also, given the severity of plague, I doubt that a generic short term dose of empiric antibiotics would cure a real case of plague.

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  12. In response to Stella, she makes a very interesting point about the migration of the black rat. Although most of these poorer countries are not as industrialized, it should still be a topic of discussion. If the black rats migrate often as shown in the genetic mapping, then these countries and organizations need to focus more on controlling the population of these rodents. All it would take to spread to another country is a large exportation of products to take place, and a few rats to get placed on board, and the disease has just spread to another continent. For example, how many times NYC has promoted keeping the subways clean, and there are so many workers employed in them and cleaning constantly. Yet there are still several rats... Control the rat population, control the disease.

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  13. Nicole's article on the WHO meeting is very interesting and is very informative about the different topics discussed about the plague. As Gul pointed out, although there is currently no vaccine in the U.S. for pneumonic plague, cases should be treated within 24 hours with an antibiotic such as tetracycline, fluroquinolone, or streptomycin. (http://www.bt.cdc.gov/agent/plague/faq.asp) Also, I came across from the paper that after the Surat incidence, steps in handling plague outbreak had been improved, and the situation fared much better in 2002 in the Himachal Pradesh outbreak.

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  14. Bobbin brings up an interesting case of pneumonic plague in Surat, India that occurred in 1994. While there were 52 deaths and widespread panic, the origin of the Yersinia Pestis that caused the plague is still unknown. This is in stark contrast to the methods presented by the article on the podcast where genetic mapping allowed for extensive characterization of the organism and precise information about its origins.

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  15. Sorry, I posted a comment on 10/14/11, but somehow it is not appearing with the other comments. I will retype the comment.

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  16. This is an interesting article and although plague has a more historical significance then as a current threat the techniques used to trace its spread might be useful for other diseases as well. The fact that they have samples from more then fifty years ago is worth noting and how that might have impacted their findings is something I wish was discussed further. Especially in relation to studies that might be done in other hot spots like the DRC which might not have samples that old.

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  17. I agree with what Stan said; the historical significance of the plague and the techniques used to trace its spread have been useful. Even as new diseases develop, we must not overlook the importance of following the basic techniques in outbreak investigations. The plague once ravaged most of the European population and the fact that it still exists today, in places like Madagascar is very interesting; even with advances in medicine and treatments, it is almost impossible to completely eradicate diseases from the planet, which will undoubtedly bring about issues of resistance.

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