Western Iranian Plague Foci Still Active, 2011-2012

In a letter in this month’s Emerging Infectious Diseases, an Iranian and French team of epidemiologists report that the old plague focus in western Iran bordering Kurdistan is still active. Between 1947 and 1966 there were nine human plague epidemics causing 156 human deaths.  The last recorded human case occurred in 1966 and in animals in 1978. No surveys for plague were conducted for the following 30 years. It is unlikely to be a coincidence that the Iranian Revolution also began in 1978.

During the summers of 2011 and 2012, the team captured and tested for the plague F1 antibody 98 rodents and counted their fleas, finding only one rodent with antibodies (1.08%). They also tested 117 sheepdogs finding 4 positive dogs or 3.42%.  In dogs, plague antibodies only last about six months suggesting that these sheepdogs must have had recent infections.  This is enough to suggest that the plague foci is still present in western Iran. Moreover, they believe the number of reservoir rodents and fleas per rodent (Xenopsylla species index 4.10) is “most favorable” circumstances for an epizootic. With plague antibodies found in the only area surveyed in 30 years, it is clear that surveillance needs to not only continue but expand extensively.

Reference:

Esamaeili S, Azadmanesh K, Naddaf SR, Rajerison M, Carniel E, & Mostafavi E (2013). Serologic survey of plague in animals, Western Iran. Emerging infectious diseases, 19 (9) PMID: 23968721

7 thoughts on “Western Iranian Plague Foci Still Active, 2011-2012

  1. Michelle, a very interesting post. Do you think you could offer some more comment on something that puzzled me? They say in the study that “the detection of Y. pestis–specific IgG in 1.02% of
    trapped rodents and 3.42% of sentinel dogs is highly suggestive of active circulation of Y. pestis in its natural animal reservoir.” Obviously, *any* Y. pestis is indicative of active circulation, but the percentage in the rodents seems exceptionally low. Earlier, they had said that of the four main rodent reservoir species, two were resistant and two susceptible. Is there something about the combination of resistance and susceptibility that adds up to low antibody rates in the rodent populations overall?

  2. Without having read the papers they cite its hard to say what they mean by a resistant reservoir animal in a paper from 1978. 63 out of 98 (64%) are only one species, Meriones persicus (Persian jird) and most of the rest Meriones libycus (Libyan jird). Interesting…. Yersinia pestis found in the recent reactivation of the Libyan focus was most closely related (but distinct from) a species from Iranian kurdistan in 1947-51 (https://contagions.wordpress.com/2013/01/20/reactivation-of-ancient-plague-foci-in-libya-2009/). I should note here that both of these rodents are apparently found throughout most of the Middle East and Central Asia.

    I think this is a pilot study. They surveyed 2000 sq. kilometers for four summer months and only caught about 50 rodents a year? Their flea numbers are also very different from 2011 to 2012. Anyway, I doubt that they have zeroed in on focus areas. They also don’t mention surveying dead animals or colonies. The dogs are more interesting to me since they would be capturing sick animals. The dogs probably cover the area better than their traps.

    Overall, I would think that after 30 years of no surveillance and all that has gone on in Iran since 1978, the plague surveillance program is starting over nearly from scratch. With a 30 year gap, they have lost an entire generation of plague surveillance workers. I take this just to be an initial signal that the focus is still active with more hopefully to follow.

    1. Monica, as Michelle said, this was somehow a pilot study. We were not sure if could find any trace… I do not recall which type of jirds had the antibody, but I assume It has been a resistant one. I will ask Ehsan Mostafavi to leave you a comment on that. Finding just one seropositive jird was not enough to publish it, but finding positive dogs was very assuring.
      We didn’t find any dead animal in the region during this study.I think the success rate of our traps were also low, which may reflect small population size of the jirds.
      Anyway, the important point is the presence of thin infection in the region, and we have planned for wider studies.

      1. Kayhan, Thanks for stopping by. As you say, if the jird population is very small that could account for how thin the positive results were. Although it must be significant for Yersinia pestis to still be present if their host has decreased from past levels. Is it possible that the dogs were becoming exposed from another host species?

  3. Iranian Kurdistan is the plague reservoir that was meticulously studied from the late 1940s to the early 1960s by Marcel Baltazard from a branch of the Pasteur Institute in Teheran. This is where he demonstrated that Yersinia pestis can subsist for months in rodents’ burrows, outside the host.

  4. Dear all,
    Thanks for your comments and your interests to this study. I am the corresponding author of this paper and the head of Research centre for emerging and reemerging infectious diseases of Pasteur institute of Iran. The seropositive rodent in our study was Meriones persicus, which is resistant to Plague.
    As Kayhan mentioned, it was a kind of pilot study. In our new round of study, we have trapped more rodents and we paid more attention to the death rodents. I also think that carnivores such as dogs are very important sentinel hosts to show the existence of Plague in a region that there has been no data for many years.
    The results of recent studies also showed the existence of Tularemia in this region. We found a high rate of seropositive human samples. The results will be published in International journal of infectious disease soon.

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