The summer is officially over this week so its time for my quarterly reading update. I read a more eclectic mix of topics this summer than usual. These are just those that really stood out as being useful for my purposes. I hope you find something of interest!
Gregory Aldrete. Floods of the Tiber in Ancient Rome. 2006.
Robert Sallares, Malaria and Rome: A History of Malaria in Ancient Italy, 2002
Nukhet Varlik. Plague and Empire in the Early Modern Mediterranean: The Ottoman Experience 1347-1600. Cambridge UP, 2015
Katharine Dean. Modeling plague transmission in Medieval European cities. (2015, June 1). MA Thesis. Oslo.
Kimura, H., Saitoh, M., Kobayashi, M., Ishii, H., Saraya, T., Kurai, D., et al. (2015). Molecular evolution of haemagglutinin (H) gene in measles virus. Scientific Reports, 1–10. doi:10.1038/srep11648
Scheidel, W. (2015). Death and the City: Ancient Rome and Beyond. Available at SSRN 2609651.
Smith-Guzmán, N. E. (2015). The skeletal manifestation of malaria: An epidemiological approach using documented skeletal collections. American Journal of Physical Anthropology, n/a–n/a. http://doi.org/10.1002/ajpa.22819
Sigl, M., Winstrup, M., McConnell, J. R., Welten, K. C., Plunkett, G., Ludlow, F., et al. (2015). Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature. http://doi.org/10.1038/nature14565
Kostick, C., & Ludlow, F. (2015). The dating of volcanic events and their impact upon European society, 400-800 CE (Vol. 5, pp. 7–30). Post-Classical Archaeologies.
Schats, R. (2015). Malaise and mosquitos: osteoarchaeological evidence for malaria in the medieval Netherlands. Analecta Praehistoricaleidensia, 45, 133–140.
Eisen, R. J., Dennis, D. T., & Gage, K. L. (2015). The Role of Early-Phase Transmission in the Spread of Yersinia pestis. Journal of Medical Entomology, tjv128–10. http://doi.org/10.1093/jme/tjv128
The old paradigm is dead! Long live the new paradigm!
Rebecca Eisen, David Dennis, and Kenneth Gage just published an article gathering all the evidence that should put an end to the blocked flea model as the only significant method of plague transmission. They summarize the data proving that unblocked fleas can and do transmit Yersinia pestis at levels that readily cause infection in rodents and humans. They call all transmission by unblocked fleas early phase transmission (EPT), even in flea species that never block.
Important findings summarized:
The blocked flea model – that only a biofilm blocked Xenopsylla cheopis which can not eat so it tries to aggressively feed and regurgitates high numbers of Yersinia pestis into the bite site – is insufficient to account for either epizootics or large human outbreaks. Blocked fleas do transmit the plague but are simply insufficient to account for the speed and volume of epizootic and epidemic transmission.
Transmission can occur as quickly as the very next blood meal taken by the flea, at times within 1-2 hours. Y. pestis does not need to replicate in the flea for transmission to occur. This makes it much more likely that the flea will survive long enough to transmit the infection.
Early phase transmission has been experimentally observed to cause infections after exposure to a single Oropsylla montana flea. Therefore, exposure to large numbers of unblocked infected fleas is not required for transmission. Epidemiologic findings suggest that most US cases come from bites from a single or at most a few fleas, and this is consistent with findings around the world where fleas that do not block are primary vectors.
Many reservoirs of plague are maintained by fleas that never block. Prairie dog reservoirs in the western US and great gerbil reservoirs in central Asia are both maintained by fleas that are never blocked by a biofilm.
“In short, EPT was observed in all flea species evaluated at varying temperatures. Transmission occasionally occurred as early as 3 h post-infection but usually was observed over 1-4 dpi [days post infection]. Although all flea species tested were capable of EPT, efficiency in these studies varied among species, suggesting that some fleas are likely to be more important than others in the rapid spread of plague in nature, especially those that are both efficient transmitters and abundant on susceptible hosts.” (p. 3)
Strains of Y. pestis that can not form a biofilm transmit as effectively by EPT as biofilm competent strains. Virulence factors that are necessary for biofilm production are not necessary for EPT.
EPT – compared to a contaminated “dirty needle” – is a mechanical form of transmission that “requires no modification or multiplication of the pathogen in the vector for transmission to occur” (p. 4).
In the pre-antibiotic era, many human bubonic plague infections and all septicemic and pneumonic cases would have produced bacteremia levels sufficient to infect fleas for EPT. In the 71 fatal plague cases recorded by the CDC between 1956 and 2013, 86.8% were either primary or secondary septicemic cases.
“Epidemic support in favor of interhuman flea borne transmission comes from records of limited bubonic plague outbreaks in isolated rural communities under exceptional circumstances of heavy human flea infestations, high familial attack rates, and a lack of evidence for concurrent rat-flea borne plague. … [studies in Africa, the Middle East and the Andes mentioned]… Based on epidemiologic pattern of person to person spread, especially the high attack rates among contacts of the sick, an absence of domestic rats, and an unusual abundance of P. irritans infesting villages and their homes, investigators concluded that the outbreak resulted from infective bites by P. irritans.” (p. 7-8)
They note that interhuman plague transmission by pulex irritans has been documented early in the 20th century and supported by laboratory experiments. As covered here a year ago, infected Pulex irritans were recovered from the homes of plague patients in Madagascar in 2013. They end with a call for more work on P. irritans to evaluate its role in modern and historical human epidemics.
It is worth noting here that throughout the article they cite many studies using many different fleas. EPT studies have also been demonstrated for mouse fleas (Aetheca wagneri Baker) and cat fleas (Ctenocephalides felis). I’ve never really understood why studies of historic plagues often overlook mice as a source of fleas.
I also have to add that mechanical transmission by the flea makes a lot of evolutionary sense. It gives evolution a place to start tinkering. ‘Good enough’ is the stuff of evolution! Optimization only occurs after a very long evolutionary process, and may never be achieved. The fact that X. choepis evolved a method (via bioflim blockage and regurgitation [LPT]) to keep transmission going longer does suggest that the rat flea has been historically important to Y. pestis evolution. Obviously mechanical transmission has also allowed Y. pestis to expand into areas and exploit new opportunities where a more complicated, required transmission system would have been an obstacle.
Experiments proving that EPT is possible have been scattered over the last 50 years! And, yet the old paradigm still reigned. Why? Obviously there has been a lack of communication within science and between science and the humanities. It would really be helpful for a historian of 20th century science to look into how this could have happened.
Following on a successful session last year, I’m offering another session on Medieval Landscapes of Disease this year at Kalamazoo.
In recognition that diseases are manifestations of their environment, this session seeks papers that place medieval diseases within their environmental context. Just as a seed must be placed in good soil to grow, infectious disease requires a permissive environment to develop into an epidemic (or epizootic) and an ideal environment to bloom into a pandemic or panzootic. I am open to all manner of studies and disciplines that address these issues.
Examples of acceptable topics:
Historic impacts of epidemics and/or epizootics
Endemic disease in medieval environments
Environmental causes of disease such as malnutrition or industrial pollution related disease
Health effects of human-animal interactions
Applications of the One Health Approach to medieval disease
Archaeological assessments of human health and disease
Landscape alterations intended to improve human or animal health
Ecology of the built environment
Abstracts of no more than 300 words and the Participant Information Form should be sent to Michelle Ziegler at ZieglerM@slu.edu by September 15.Deadline extended to Friday September 18. Pre-submission queries are welcome.