Data source: Hospital Authority, Hong Kong
Map created by CUHK SpatioEpi Group
Since August 2017, there has been an ongoing outbreak of plague in Madagascar, Africa. Within 2.5 months (1 Aug - 15 Oct 2017), more than 800 cases were reported, including at least 60 deaths. Thirty-seven out of 114 districts of the country have reported cases (http://www.afro.who.int/health-topics/plague/plague-outbreak-situation-reports). Seychelles, Madagascar's nearby country, has also reported imported cases.
In 1990s, plague prevailed in Asia and Africa, as shown in the map. While plague was still widespread in Africa, the number of reported cases in Asia was small in the following decade (2000-2009). In 2010 and thereafter, the annual number of reported cases in Africa dropped significantly to below 1000. However, the outbreak in Madagascar this year is becoming a concern, as it pushes the epidemic curve up again.
Plague is transmitted through the bite of infected animal's (mainly rodent) fleas. It can be classified as bubonic plague, pneumonic plague and septicaemic plague. Pneumonic plague can spread through respiratory droplets and is highly contagious. Around two-third of reported cases in the current outbreak in Madagascar were pneumonic plague. At least 39 healthcare workers were infected.
Data for the map were extracted from WHO.
Plague is caused by the bacteria Yersinia petis, which is transmitted from rodent to rodent by infected fleas. If bitten by an infected flea, a person usually develops a bubonic form of plague, which is characterised by a swelling of the draining lymph node. While bubonic plague is the commonest, there are also the septicaemic form and pneumonic form. Septicaemic plague occurs when infection spreads directly through the bloodstream, while the pneumonic form is the most virulent but least common. Plague also spreads from human to human by inhalation of aerosolised infective droplets, in the absence of flea or animal.
A Hong Kong outbreak of plague occurred in Tai Ping Shan of Sheung Wan District in 1894. In fact, the bubonic plague bacillus was isolated in Hong Kong at that time by Alexandre Yersin from France.
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