30. yersinia, francisella, and burkholderia

what major human disease does yersinia pestis cause?

the black plague

what region of the US is affected by human plague?

mainly western states (colorado, california, idaho, wyoming)

yersinia gram stain

gram negative, bipolar-staining coccobacilli

what is the main source/reservoir host of yersinia?

rodents (rats in urban areas; wild rodents such as ground squirrels)

what is yersinia’s key vector?

rat flea (xenopsylla cheopis)

(does not transmit well in ctenocephalides)

how is yersinia transmitted?

• fleas (most common)

• ingestion (cats eating infected rodents)

• aerosols (occasionally → host-to-host transmission)

what are yersinia’s main virulence factors?

encoded in plasmids

• pMT1: capsule (F1)

• pCD1: type III secretion system + Yop toxins (interfere with phagocytosis and antimicrobial responses) + LcrV (facilitates injection of Yop proteins into host cells & reduces cytokine secretion)

• pPCR1 (plasmid encoded) → expresses virulence factors that activate the coagulation cascade → thrombosis

why are yersinia virulence factors expressed in mammals and not flea vectors?

expression of some virulence factor genes is temperature sensitive → expressed at mammalian body temperature

(fleas have lower body temperatures)

how is yersinia transmitted in fleas?

biofilm formation blocks flea gut and allows bacteria to remain in upper mouth parts → regurgitated and transmitted to new host when flea takes blood meal

what is the primary lesion seen in humans (yersinia)?

ulcer at site of flea bite

bubonic form (yersinia)

secondary lesion: bubos → bacteria in lymph nodes (pus-filled swelling)

septicemic form (yersinia)

bacteria disseminates into bloodstream → pPCR1 (plasmid) contains virulence factors that activate coagulation cascade → thrombotic events and disseminated intravascular coagulation

pneumonic form (yersinia)

• rare form

• shorter incubation period (2-4 days)

• death in 24-72 hours following appearance of clinical signs

• more infectious

yersinia diagnosis

• visualization on blood smears or needle aspirates of bubos

• culture

• serology (F1 ELISA) & PCR

yersinia control/prevention

• zoonotic and reportable

• kill fleas before rodents

• flea control (pets)

• improve sanitation in urban areas (↓ rodent infestations)

• monitor wildlife (rural)

francisella tularensis gram stain

gram negative coccobacilli

francisella tularensis source

wildlife (rabbits = most common source)

compare the different subspecies of francisella tularensis that cause human/animal disease

• susbp. tularensis (type A)

  • mostly north america

  • cause of sporadic outbreaks in US

  • associated with more severe disease (more virulent)

• subsp. holarctica (type B)

  • worldwide (europe, asia, n. america)

  • waterborne disease; sporadic outbreaks in US

  • milder clinical signs (less virulent)

francisella tularensis transmission & forms of tularemia

transmission route determines clinical signs

• contact or bite (insect or animal) → ulceroglandular form (most common)

• ingestion → oropharyngeal / intestinal / typhoidal form

• inhalation → pneumonic form (human disease)

• eye exposure → oculoglandular form (human disease)

what domestic species does tularemia (francisella tularensis) affect?

rare in dogs and cats (but more likely in cats)

francisella tularensis virulence factors

important for intracellular invasion and survival

• LPS

• macrophage growth locus (A & B)

• francisella pathogenicity island (FPI)

francisella tularensis pathogenesis

in all forms, bacteria are engulfed by macrophages, escape the phagosome and replicate within the host cell → cell dies, releasing bacteria into tissue → local spread → granulomas

francisella tularensis clinical signs

• fever

• anorexia

• lethargy

• enlarged lymph nodes

• draining ulcers

• ± nasal discharge

francisella tularensis diagnosis

in people, usually serology

• due to zoonotic risk, few labs will perform culture

francisella tularensis treatment

• zoonotic and reportable disease

• antibiotics (streptomycin, aminoglycosides, or tetracyclines) for at least 3 weeks

• sensitivity testing recommended

burkholderia gram stain

gram negative bacilli

burkholderia sources

environment, swampy soils, colonizes amoebas

what are the host ranges of the burkholderia species? what diseases do they cause?

• b. mallei → mainly equids (zoonotic potential)

  • cause “glanders”

• b. pseudomaellei → humans, domestic ruminants, horses, dogs, cats

  • cause meliodosis

which animals are most susceptible to meliodosis? (b. pseudomaellei)

• highly susceptible: goats, sheep, pigs, camels, alpacas/llamas

• moderately susceptible: cattle, horses, dogs, cats

what animals are accidental hosts for b. mallei?

• cats, dogs, goat/sheep, camels

  • NOT cattle, pigs, poultry, or rodents

• zoonotic potential

burkholderia virulence factors

• adhesins → help attach to amoeba

• type III secretion system

• capsule

burkholderia transmission

• contact with contaminated soil or water

• organisms may be ingested, inhaled (aerosol), or introduced into broken skin

burkholderia pathogenesis

• pyogranulomas wherever it infects

• following entry, becomes facultative intracellular pathogen in phagocytic cells and will spread to various organs

  • lungs, spleen, liver, and associated lymph nodes commonly affected

burkholderia diagnosis

primarily by culture (selective media, fastidious) and molecular testing (PCR, WGS)

burkholderia treatment

• difficult with guarded prognosis

• expensive and prolonged

is burkholderia zoonotic?

• no → can cause infections in humans but could be acquired from environment

• is a public health concern