Two recent outbreaks of plague in Libya and Algeria are likely due to re-emergence or re-activation of ancient Yersinia pestis from the local area, rather than recent importation from the same distant source, suggest study findings.
Researchers led by Elisabeth Carniel from the Institut Pasteur in Paris, France, found that the plague outbreak in Algeria in 2003 was caused by Y. pestis strains of the Orientalis biovar lineage, whereas the 2009 outbreak in Libya was caused by strains of the Medievalis biovar lineage showing that the two outbreaks were not linked.
They believe that unusual climatic conditions in the Tobruk area of Libya may have precipitated the re-emergence of Y. pestis in 2009. Prior to the outbreak, which affected five people, there was a very humid winter and an exceptional harvest triggering a massive expansion in the flea and rodent population. They note that unusual climatic conditions have been recorded before earlier outbreaks of plague.
Although modern anti-microbial treatment has dramatically improved the extent of illness and reduced the number of deaths occurring as a result of Y. pestis infections, the disease has not been eradicated.
In addition to the small 2009 outbreak in Libya and the 2003 Algerian outbreak, which affected 18 people, other sudden outbreaks have been reported around the world since 1990 in countries that had previously experienced no plague cases for decades and where the disease was thought to be eliminated, such as in India, in 1994.
Prior to 2009, the most recent Libyan outbreak was in 1984, with smaller outbreaks in 1977, 1976, and 1972. In Algeria the most recent cases prior to 2003 were recorded in the 1940s.
On laboratory analysis of the Y. pestis Medievalis strain collected in Libya, Carniel and colleagues found that it was genetically closest to strains from the Iranian part of Kurdistan, and say that the outbreak was most likely due to reactivation of established local plague foci originating from ancient importation from central Asia.
In contrast, the Y. pestis Orientalis strains from the 2003 outbreak in Algeria were most genetically similar to the Y. pestis Orientalis strain that caused the 1944 outbreak in Algeria.
"Recent reemergence of these independent foci suggests that climatic and environmental changes in northern Africa may be favorable for the Y. pestis epidemiologic cycle," write the authors in Emerging Infectious Diseases.
"Thus, other countries in northern Africa that have had plague foci may also be at risk for plague outbreaks in the near future."
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