A second clade included both Alastrim minor (a phenotypically mild smallpox) described from the American continents and isolates from West Africa which diverged from an ancestral strain between 1,400 and 6,300 years before present. This clade further diverged into two subclades at least 800 years ago.A second estimate has placed the separation of variola from Taterapox (an Orthopoxvirus of some African rodents including gerbils) at 3,000 to 4,000 years ago. This is consistent with archaeological and historical evidence regarding the appearance of smallpox as a human disease which suggests a relatively recent origin. If the mutation rate is assumed to be similar to that of the herpesviruses, the divergence date of variola from Taterapox has been estimated to be 50,000 years ago. While this is consistent with the other published estimates, it suggests that the archaeological and historical evidence is very incomplete. Better estimates of mutation rates in these viruses are needed. Examination of a strain that dates from c. 1650 found that this strain was basal to the other presently sequenced strains. The mutation rate of this virus is well modeled by a molecular clock. Diversification of strains only occurred in the 18th and 19th centuries. Virology
Variola is a large brick-shaped virus measuring approximately 302 to 350 nanometers by 244 to 270 nm, with a single linear double stranded DNA genome 186 kilobase pairs (kbp) in size and containing a hairpin loop at each end. The two classic varieties of smallpox are variola major and variola minor.
Most of the infections in Peru were bubonic plague, with four cases of pneumonic plague.The first recorded plague outbreak in Peru was in 1903. Prior to the above case, the last known outbreak was in 1994, killing 35 people. Madagascar
In November 2013, an outbreak of plague occurred in the African island nation of Madagascar. As of 16 December, at least 89 people were infected, with 39 deaths with at least two cases involving pneumonic plague. However, as many as 90% of cases were later reported to have involved pneumonic plague.From 23 August to 30 September 2017, a total of 73 suspected, probable, and confirmed cases of pneumonic plague, including 17 deaths, were reported in Madagascar. The diagnosis was confirmed by the Institut Pasteur de Madagascar by a polymerase chain reaction test, while field health workers used a Rapid Diagnostic Test. The WHO and Institut Pasteur de Madagascar were both involved in administering antibiotic compounds and attempting to stop the spread of the disease. By mid-October, there were an estimated 684 confirmed cases of plague with 474 pneumonic, 156 bubonic and one septicemic. The remainder were not classified. At least 74 deaths have been ascribed to pneumonic plague.The outbreak officially ended on 26 November 2017 with 2,348 cases and 202 deaths officially reported. United States
In the fall of 1924, an outbreak occurred in Los Angeles that killed 30 people. On 2 November 2007, wildlife biologist Eric York died of pneumonic plague in Grand Canyon National Park.