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It's deadly without treatment. It's also very contagious because the plague can spread through the air when a person coughs. Symptoms include. “If you look at how the Black Death spread,” says Susan Scott, one of the . Human fleas can keep it in their guts for a few weeks, leading to a. The plague was thought to have been largely transmitted by have been down to the rats, but instead can be “largely ascribed to human fleas.
This is called the enzootic cycle. Occasionally, other species become infected, causing an outbreak among animals, called an epizootic.
Ecology and Transmission
Humans are usually more at risk during, or shortly after, a plague epizootic. Scientific studies have suggested that epizootics in the southwestern United States are more likely during cooler summers that follow wet winters. Epizootics are most likely in areas with multiple types of rodents living in high densities and in diverse habitats.Human Population Through Time
Transmission The plague bacteria can be transmitted to humans in the following ways: Plague bacteria are most often transmitted by the bite of an infected flea. During plague epizootics, many rodents die, causing hungry fleas to seek other sources of blood. People and animals that visit places where rodents have recently died from plague are at risk of being infected from flea bites. Dogs and cats may also bring plague-infected fleas into the home.
Flea bite exposure may result in primary bubonic plague or septicemic plague. Contact with contaminated fluid or tissue. Humans can become infected when handling tissue or body fluids of a plague-infected animal. For example, a hunter skinning a rabbit or other infected animal without using proper precautions could become infected with plague bacteria.
This form of exposure most commonly results in bubonic plague or septicemic plague. Despite the historical significance of the disease, the mechanisms underlying the spread of plague in Europe are poorly understood.
While it is commonly assumed that rats and their fleas spread plague during the Second Pandemic, there is little historical and archaeological support for such a claim. Here, we show that human ectoparasites, like body lice and human fleas, might be more likely than rats to have caused the rapidly developing epidemics in pre-Industrial Europe.
Such an alternative transmission route explains many of the notable epidemiological differences between historical and modern plague epidemics. Today, most human plague cases are bubonic, caused by spillover of infected fleas from rodent epizootics, or pneumonic, caused by inhalation of infectious droplets.
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However, little is known about the historical spread of plague in Europe during the Second Pandemic 14—19th centuriesincluding the Black Death, which led to high mortality and recurrent epidemics for hundreds of years. Several studies have suggested that human ectoparasite vectors, such as human fleas Pulex irritans or body lice Pediculus humanus humanuscaused the rapidly spreading epidemics.
Here, we describe a compartmental model for plague transmission by a human ectoparasite vector. Using Bayesian inference, we found that this model fits mortality curves from nine outbreaks in Europe better than models for pneumonic or rodent transmission. Our results support that human ectoparasites were primary vectors for plague during the Second Pandemic, including the Black Death —ultimately challenging the assumption that plague in Europe was predominantly spread by rats.
From the Cover: Human ectoparasites and the spread of plague in Europe during the Second Pandemic
Plague, caused by the bacterium Yersinia pestis, has been extensively studied due to its modern and historical significance. In the past, plague has famously caused at least three pandemics in human history: Today, plague persists primarily in rodent reservoirs in Asia, Africa, and the Americas, where it poses a recurrent threat to nearby human settlements 2. The most common forms of plague infection are bubonic and pneumonic 2.
Bubonic plague occurs when bacteria enter the skin, usually from the bite of an infected flea vector. Primary pneumonic plague occurs when aerosolized bacteria enter and infect the lungs.
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Pneumonic plague can also arise as a complication of bubonic or septicemic infections 2known as secondary pneumonic plague. Individuals with pneumonic plague can transmit the disease through the respiratory route, although outbreaks of pneumonic plague are typically small because infected persons die rapidly without treatment 5.
Septicemic plague occurs when bacteria infect the bloodstream, commonly from a primary pneumonic or bubonic infection 2.
A central focus of historical plague research has been to understand the spread and persistence of plague in Europe. Little is known about the transmission of plague in Europe, the Middle East, and North Africa during the Second Pandemic, including the Black Death, when the disease killed an estimated one-third of the population.