Lecture 13: Zoonotic Infections Flashcards
Yersinia Pestis and Rickettsial Dieseases
True or False: There is no vaccine against Yesinia pestis (causes plague).
False: A formalin-inactivated vaccine is available, but severe inflammatory reactions are common; Protects for up to 12 months – regular booster shots required.
What is zoonosis?
An infection where the causative microbe is maintained in an animal reservoir and transmitted to humans.
What bacterium causes bubonic plague?
Yersinia pestis.
What are the characteristics of Yersinia pestis?
It is a short, pleomorphic, Gram-negative coccobacillus, facultative anaerobe, non-motile, and non-spore-forming.
What family does Yersinia pestis belong to?
Enterobacteriaceae.
How does Yersinia pestis appear under a Giemsa stain?
It has a “safety-pin” appearance due to bipolar staining, where the ends of the bacterium take up more stain than the middle.
How does Yersinia pestis behave on blood agar?
It is non-haemolytic, and colonies undergo autolysis after 2-3 days.
What are the three Yersinia species of concern to human health?
Yersinia pestis, Yersinia enterocolitica, Yersinia pseudotuberculosis.
How is Yersinia pestis related to Yersinia pseudotuberculosis?
Yersinia pestis evolved from Yersinia pseudotuberculosis, and they share ~90% genetic similarity.
What disease does Yersinia enterocolitica cause?
Gastroenteritis with occasional severe complications.
What disease does Yersinia pseudotuberculosis cause?
Fatal septicaemia in animals and zoonotic infections in humans, often causing mesenteric adenitis.
What are the symptoms of plague?
General malaise, high fever, tender lymph nodes (buboes), septicaemia, disseminated intravascular coagulation, convulsions, and death due to endotoxic shock.
How is bubonic plague transmitted?
Through flea bites from infected wild rodents.
How is pneumonic plague transmitted?
Human-to-human via aerosol droplets if the infection reaches the lungs.
What is special about the encoding of virulence in Yersinia pestis?
Its virulence is plasmid-encoded, not genome-mediated.
What does the Pla gene in Yersinia pestis encode?
A plasminogen activator that degrades complement factors, helping the bacteria evade phagocytosis.
What are Yop proteins?
Yersinia outer proteins that prevent phagocytosis, disrupt the cytoskeleton, and induce macrophage apoptosis.
How do Yop proteins enter host cells?
Via a Type III secretion system, injecting directly into macrophages.
Why is it difficult to eradicate Yersinia pestis?
It is maintained in an animal reservoir, making control challenging.
How effective are antibiotics against Yersinia pestis?
Antibiotics like streptomycin and tetracycline are effective if given early.
Why is antibiotic resistance in Yersinia pestis low?
It is a rare disease with little selective pressure from antibiotics.
What are Rickettsial diseases?
Diseases caused by small, Gram-negative, obligate intracellular bacteria.
How are Rickettsial diseases transmitted?
From animals to humans via arthropod bites.
Can Rickettsial diseases spread from human to human?
No, human-to-human transmission does not occur.
