plague

features of yersinia pestis

rod shaped bacteria, from enterobacteriaceae family, gram negative, facultative anaerobes

2 main habitats of yersinia pestis

gut of a flea at ambient temperature, blood/tissues of a mammalian host at body temperature

other examples of host species

marmots, gerbils, squirrels, guinea pigs

why is the cycle more sustainable in the wild

some wild rodents are relatively resistant to plague and aren't harmed as much, so they form permanent foci of infection

how many species have been found infected with YP

around 80

4 mechanisms causing differences in vector efficiency are:

insect immunity, midgut digestive enzymes (pathogen has to evade). frequency of feeding and defecation, flea life span after infection

transmission by flea - infection to transmission

becomes infected after a blood meal, pathogen replicates and disseminates in vector, remains confined to flea, digestive tract and doesn't adhere to midgut epithelium. can be transmitted via regurgitation or in faeces

YP persistence in the flead depends on 3 factors:

formation of multicellular aggregates (too large to be passed in faeces), ability to form a biofilm which creates a blockage in proventriculus, when biofilm grows it fills the lumen, and blocking the PV enhances regurgitative transmission

why does YP have high pathogenicity

able to overcome host defences and multiply extracellularly within the body, YP inducesa local lesion and inflammation, the toxins produced by the pathogen are what causes the harm

what damage does the toxin produced do

endothelial damage and necrosis, leads to vascular destruction and local haemorrhaging

3 major recorded plague pandemics + dates

justinianic plague - 541, black death - 1347, modern plague - 1894

plague symptoms

2-4 days incubation period, flu like - fever, chills, head/body aches, weaknesses, vomiting/nausea

3 forms of plague

bubonic, septicaemic, pneumonic

bubonic - spread and symptoms

usually from infected flea bite, bacteria multiply at site of entry and spread via lymphatic system to lymph nodes - nodes become painful and enlarged, forms buboes

septicaemic effects

blood poisoning - can occur when infection spreads to bloodstream - can lead to meningitis, endotoxic shock and disseminated intravascular coagulation

pneumonic - spread and symptoms

usually caused by infection spreading to lungs from bubonic, or from person-person transmission, causes acute pulmonary insufficiency, sepsis and toxic shock

3 methods of transmission

flea bites, contact with contaminated fluid/tissue, infectious droplets

diagnosis method

visualisation of bipolar staining, ovoid, gram-negative bacteria

treatment

antibiotics - streptomycin, tetracyclin etc, supportive therapy

how did YP evolve to become highly pathogenic

selective loss of gene function enabled YP to form a biofilm in flea gut, for regurgitative transmission