Plague

Definition

Plague is a severe infectious disease caused by the bacterium Yersinia pestis, primarily transmitted through the bites of infected fleas, which are often carried by rodents. This disease has historically led to devastating pandemics, including the infamous Black Death in the 14th century. The connection between plague and insects as disease vectors highlights the crucial role that fleas play in the transmission of this lethal pathogen to humans and other mammals.

5 Must Know Facts For Your Next Test

1. Plague can manifest in three forms: bubonic, septicemic, and pneumonic, each presenting different symptoms and modes of transmission.
2. Bubonic plague is characterized by swollen lymph nodes, called buboes, while septicemic plague occurs when the bacteria enter the bloodstream.
3. Pneumonic plague is the most severe form, affecting the lungs and can be transmitted from person to person through respiratory droplets.
4. The primary vector for plague is the rat flea (Xenopsylla cheopis), which becomes infected by feeding on an infected rodent.
5. Plague outbreaks can be controlled through public health measures that focus on rodent population management and flea control to break the transmission cycle.

Review Questions

• How does Yersinia pestis use insects as vectors in the transmission of plague?
  • Yersinia pestis utilizes fleas as vectors to spread plague by infecting these insects when they feed on infected rodents. The bacteria multiply within the flea's gut, causing a blockage that forces the flea to feed more aggressively on its hosts. This leads to higher rates of transmission as fleas are more likely to bite humans or other mammals when they are starved due to their inability to ingest blood properly. Consequently, when an infected flea bites a human, it can introduce the bacteria directly into their bloodstream.
• Discuss the different forms of plague and how their modes of transmission vary.
  • Plague presents in three main forms: bubonic, septicemic, and pneumonic. Bubonic plague is typically transmitted through flea bites from infected rodents and causes painful swellings called buboes. Septicemic plague occurs when the bacteria enter the bloodstream and can arise from untreated bubonic cases or direct contact with infected tissues. Pneumonic plague is a more contagious form that develops when Yersinia pestis infects the lungs, allowing it to spread between humans through respiratory droplets. Each form has distinct clinical features and implications for public health responses.
• Evaluate the historical impact of plague outbreaks on human populations and how these events have shaped modern public health responses.
  • Historical outbreaks of plague, particularly during the Black Death in the 14th century, decimated populations across Europe and Asia, leading to profound social and economic changes. These pandemics highlighted the need for improved understanding of disease transmission and vector control. As a result, modern public health responses now emphasize surveillance of rodent populations, management of insect vectors like fleas, and rapid response protocols during outbreaks. The lessons learned from past plague pandemics continue to inform strategies for managing current vector-borne diseases.

Related terms

Yersinia pestis: A gram-negative bacterium that is the causative agent of plague, known for its ability to form biofilms in the flea gut, aiding in its transmission.

Vector-borne diseases: Diseases that are transmitted to humans or other animals through the bite of infected arthropods, such as mosquitoes, ticks, and fleas.

Rodent reservoir: Populations of rodents that harbor pathogens like Yersinia pestis, serving as a source for infection in fleas and ultimately in humans.