Initially, it seemed like just another, now annual, outbreak. Plague is endemic in Madagascar, producing about 400 infections per year. As of October 13, there were 684 cases infections with 57 deaths. Four days later (the weekend update), the case number jumped to 804 cases and 74 deaths for a 9.3% mortality rate and pneumonic plague reached 74% of cases. Pneumonic plague is fast outrunning the bubonic form. They can not claim to have this under control while cases are climbing so quickly. It is already the largest epidemic within decades in Madagascar with the potential to become one of the largest post-third pandemic outbreaks.
Two suspected pneumonic cases have also been identified in the Seychelles, an island cluster north of Madagascar, where a large rapid response seems to have prevented continued to spread and fatalities. The Seychelles responded by banning travel from Madagascar to the Seychelles. While this is condemned by the WHO, I can understand it. They are a very small nation scattered across over 100 small islands. (Use the zoom on the map above to find the Seychelles.) They spent tremendous effort and expense responding to the import of one pneumonic case. It’s not too hard to imagine them being overwhelmed. The WHO has to keep travel open as long as possible to prevent the outbreak from devastating Madagascar’s already poor economy. Poverty fosters a deeper entrenching of plague in the country. Poverty has always been one of the drivers of the plague; it’s not a coincidence that the poor always died first in during the Plague of Justinian and the Black Death and its successor outbreaks. (WHO Update: Seychelles cases are negative for the plague.)
Additionally, eleven strains of Yersinia pestis have been isolated from this year’s cases. All are responsive to the commonly used antibiotics but it does mean that there is not a single source of the outbreak. Plague bloomed in at least several districts of the country before just one case started the pneumonic outbreak. We won’t have the detailed epidemiological data until after the epidemic. The Madagascar’s Ministry of Health is now warning that the epidemic may continue until the typical end of the season in April.
There have now been outbreaks in several years a row that strongly featured pneumonic plague, spread by aerosols person-to-person. These outbreaks are making me rethink the role of pneumonic plague in the historic epidemics. I still don’t think it was the primary transmission form in the biggest outbreaks, but perhaps it was a bigger player than current paradigms allow, especially in urban areas. Large pneumonic plague outbreaks require crowded living conditions.
I previously wrote about a 2011 Madagascar epidemic that illustrates some of the unique problems of a completely pneumonic outbreak. It had a 75% case fatality rate simply because cases could not be identified quickly enough. Once cases were identified, the normal public health response quickly contained the outbreak, linking all 20 fatalities to a single index (initial) case. As the graphic to right shows, the signs and symptoms of pneumonic plague are not very specific. If pneumonic plague reached the northern hemisphere during flu season, only coughing up blood (hemoptysis) would be distinctive, specific diagnostic tools would be needed to distinguish it from bacterial pneumonia that normally accompanies flu outbreaks. A problem here is that during large outbreaks, not every case is usually sent for specific diagnosis. Fortunately, Yersinia pestis responds to some common antibiotics so that antibiotics given for typical pneumonia may buy some time.
The 2011 pneumonic outbreak was also a relatively small example of pneumonic plague’s super-spreading ability. It is likely in the final analysis of this year’s pneumonic outbreak one or more super spreaders beyond the index case will be identified. We have seen what other super-spreaders like SARS were able to do when initial transportation screenings did not spot them. The landscape of super-spreading can be complex. The closed environment of a plane would likely expose most of the people on the plague. Cars and trucks have acted as disease hot spots for pneumonic plague in China, where traveling in enclosed spaces with the index case was a common denominator for several outbreaks. It is likely that planes and boats would have the same effect.
In the next post, I’ll look at the long-term challenges to controlling plague in Madagascar. There are some very troubling signs here for global health. In addition, it is our best living laboratory for the study of plague past and present. It is in all of our interest to help Madagascar meet its challenges.
Lisa Schnirring. (13 Oct 2017) “Plague total grows in Madagascar as response builds” CIDRAP
WHO, (15 Oct 2017) Seychelles – Suspected Plague (Ex- Madagascar)
Madagascar struggles to contain plague outbreak, France24, 10/17/2017.
Madagascar MOH: Confirmed & Suspected Plague Now Exceeds 800 Cases, Avian Flu Diary, 10/16/2017.