When climate subsequently becomes unfavorable, it facilitates collapse of plague-infected rodent populations, forcing their fleas to find alternative hosts, study shows
Photo: iStock The Oregon Health Authority confirmed a rare case of the bubonic plague infecting a resident last week. The patient was likely infected by a pet cat that acquired the Yersinia pestis bacterium found in rodents and fleas.
Close contacts of the resident and the cat have been given medication beforehand to contain the spread. “Consult a veterinarian immediately if your cat becomes sick after being in contact with rodents,” the authority warned in a press release.
In the mid-1300s, the bubonic plague was responsible for the pandemic that was infamously known as the Black Death, wiping out more than 50 per cent of Europe’s population. The bacterial infection remains today but is uncommon and treatable with modern antibiotics.
“Presently, human plague infections continue to occur in rural areas in the western United States, but significantly more cases occur in parts of Africa and Asia,” the national public health agency of the United States, the Centers for Disease and Control Prevention, said.
In the west and southwestern parts of the US, 496 cases of the plague have been documented between 1970 and 2020 by the CDC. On average, seven human plague cases are reported every year in the range of 1-17 cases per year in the US. Although the disease affects people of all groups, half of the cases occur in people aged 12-45.
The disease appears in three forms:
The World Health Organization (WHO) reports between 1,000-2,000 cases every year, while the real numbers may vary and could be higher. The disease has a case-fatality ratio of 30-100 per cent if left untreated. Plague epidemics have been reported in Asia, South America and Africa. But after the 1990s, most cases have been reported in Africa.
“The three most endemic countries are the Democratic Republic of Congo, Madagascar and Peru. In Madagascar, cases of bubonic plague are reported nearly every year, during the epidemic season (between September and April),” the WHO said.
In a study published in 2015 in the Proceedings of the National Academy of Sciences, researchers identified outbreaks of the plague that corresponded with changing climatic patterns. The researchers said that climate change may have played a role in the plague’s repeated reappearance till the 19th century.
The scientists used tree rings as a guide to establish how the climate has changed over the centuries. “Our findings support a scenario where climate fluctuations that positively affect tree-ring growth in the juniper trees in the Karakoram mountain range (in the border region of China, India, and Pakistan) also affect climate in a larger region in a way that can promote and synchronise plague outbreaks among the rodent populations of Central Asia,” the researchers stated.
“When the climate subsequently becomes unfavorable, it facilitates the collapse of plague-infected rodent populations, forcing their fleas to find alternative hosts. Such large-scale wildlife plague outbreaks in Asia would, during the time of the second plague pandemic, frequently result in the arrival of plague to Europe harbours," the scientists added.
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