Category Archives: public health

Biosecurity Failures Round-up

Like many of you, I’ve been watching and reading all the recent biosecurity lapses at our top labs with some dismay. This really isn’t something I normally would cover here on Contagions, but a comment from a reader reminded me that not everyone gets all the stories I’ve been tweeting (or retweeting) for the last few months. So here is a partial roundup in no particular order:

CIDRAP: Wholesale roster change coming for US biosecurity board

Superbug: The Leader of the Smallpox Eradication Effort Speaks About the Virus’ Rediscovery

Superbug: Virus in Found Tubes of Smallpox Is Viable

Superbug: Enhancing flu in the lab: Are accidents inevitable?

Found: Forgotten Vials of Smallpox | Science Blogs | WIRED

Exclusive: U.S. says government lab workers possibly exposed to anthrax

After Lapses,CDC Admits a Lax Culture at Labs | NYTimes

U.S. inspectors find further anthrax violations, mishandling http://www.reuters.com/article/2014/07/14/us-usa-anthrax-idUSKBN0FJ29X20140714

Transcript of CDC Press Conference on Recent Biosafety Incidents

On biosecurity at a local level: Out of the Lab & Into the Mouth These are getting to be yearly stories!

Meanwhile, elsewhere  Ebola (another category A bioterrorism agent) is raging unchecked in western Africa….

“How to Ignore a Plague” (Ebola) by Umaru Fofana

Ebola cases in West Africa reach 964, deaths top 600  http://www.cidrap.umn.edu/news-perspective/2014/07/ebola-cases-west-africa-reach-964-deaths-top-600

USAMRIID Providing Laboratory Support to Ebola Outbreak http://globalbiodefense.com/2014/07/15/usamriid-providing-laboratory-support-ebola-outbreak/#sthash.GxNfldMP.dpuf

Yersinia pestis found in human fleas, Madagascar 2013

Madagascar is consistently one of the top two countries in Africa (and usually the world) in cases of plague, caused by Yersinia pestis. For five years prior to January 2013, Madagascar registered 312 to 648 cases per year, with a majority being laboratory confirmed of which >80% were bubonic plague. Of the multiple reservoir species in Madagascar, the black rat (Rattus rattus) is the primary reservoir with Xenopsylla choepus being the main urban vector and Synopsyllus fonquerniei in rural areas.

After a nine case bubonic outbreak in the rural area of Soavina in the district of Ambatofinandrana (shown below), fleas were collected within and outside of five houses over three nights.


The team from the Institut Pasteur de Madagascar collected 319 fleas representing five genera; the most common being the human flea Pulex irritans (73.3%).  In this study, X. cheopis and S. fonquerniei were only collected outside of the houses. Pulex irritans was found only indoors where it made up 95.5% of flea species. Of the 274 fleas tested for Yersinia pestis, 9 pulex irritans were positive. These positive human fleas came from three homes, one of which had a confirmed case of human plague. None of the other flea species tested positive for plague.

Previous observations of pulex irritans in Madagascar suggest this flea may be responsible for domestic human-to-human transmission. High densities of human fleas were reported in plague outbreak villages in 2012-2013. Flea surveys on rats in Madagascar conducted over the last three quarters of a century show that pulex irritans are very rare on rats, suggesting it is not transmitting plague from rats to humans at least in Madagascar. Although pulex irritans are commonly called the human flea, they will feed on dogs and pigs  in addition to humans.  They have also been sporadically found on a variety of other mammals and birds, including rats.

Coping with human fleas as plague vectors will be a significant extra burden on the public health services of Madagascar. Ridding homes of human fleas can be a difficult task. It will however give plague researchers an opportunity to study pulex irritans as a vector in one of the top human plague producing countries in the world.

Within the last ten years, Madagascar has produced human plague cases from three different fleas and pneumonic transmission. With its diversity of plague reservoirs and now flea vectors, Madagascar is illustrating how deeply Yersinia pestis can penetrate and become entrenched in the environment.

Reference:

Ratovonjato J, Rajerison M, Rahelinirina S, Boyer S. “Yersinia pestis in Pulex irritans fleas during plague outbreak, Madagascar” [letter]. Emerging Infectious Disease. 2014 Aug [30 June 2014].http://dx.doi.org/10.3201/eid2008.130629

Wyrwa, J. 2011. “Pulex irritans” (On-line), Animal Diversity Web. Accessed July 01, 2014 at http://animaldiversity.ummz.umich.edu/accounts/Pulex_irritans/

‘Seed and Soil': an epidemiological parable

I’ve been thinking about the ‘seed and soil’ metaphor used by turn of the century by physicians who accepted germ theory but only had environmental medicine to combat infections. All classically trained physicians, whether religious or not, would have been familiar with the biblical parable of the sower. It also works well as an epidemiological parable of ‘seed and soil’, microbe and environment.  For this parable, imagine that the seeds are genetically identical microbes, only the environment varies.

Then he told them many things in parables, saying: “A farmer went out to sow his seed.  As he was scattering the seed, some fell along the path, and the birds came and ate it up.  Some fell on rocky places, where it did not have much soil. It sprang up quickly, because the soil was shallow.  But when the sun came up, the plants were scorched, and they withered because they had no root.  Other seed fell among thorns, which grew up and choked the plants.  Still other seed fell on good soil, where it produced a crop—a hundred, sixty or thirty times what was sown.” (Matt 13:3-8)

 

The seed that falls upon the path and is devoured by birds are the microbes that are deposited in a completely hostile environment, where they can not sprout (thrive) at all and are prey primarily for other microbes. Their presence is invisible to the non-microscopic world.

The seeds in rocky places that sprout only to wither are the microbes that quickly deplete their resources: viruses that run out of susceptible hosts or a zoonotic disease without sufficient vectors. There is an an initial outbreak, but it is self-limiting and does not become endemic.

Typical ‘food poisoning’ infections are a great example of a seeds that initial thrive only to be choked out by the thorns. The bacteria land in our intestines, initially thriving causing typical nausea, vomiting, and diarrhea, but within about a day our normal flora begin to out compete the foreigner. Hardly thorns, these microbes that normally reside in our intestines protect us from most pathogens. The infection usually ends without medical treatment.  Just as a pesticide can cut back the weeds (thorns), antibiotic treatment can depress the normal flora growth and give an opportunistic microbe the chance to flourish.

The seeds that fall on good moist soil are the microbes that thrive in an ideal environment , often becoming endemic. When the conditions are perfect, a super spreading event can occur with the potential to spark a regional outbreak.

No matter what tools the microbe possesses, interaction with the environment determines  its success. The environment must be permissive for any epidemic to flourish.