19. listeria

listeria gram stain

gram positive rod/coccobacilli

where is listeria typically found?

• ubiquitous in soil and water

  • not commensal

• can transiently colonize hosts without causing disease

what is the source of listeria (foodborne pathogen)?

environment and food contamination

• ex. silage not being kept at a low enough pH (<5) 

what characteristics of listeria contribute to its pathogenicity?

• survival in cold and harsh environments → not inhibited by refrigeration

• production of biofilm

• intracellular lifestyle

function of internalins

• interact with host cell receptors and allows invasion into the host cell

• important for attachment

listeriolisin O (LLO)

pore-forming toxin that allows listeria to escape from vacuole once endocytosed

ActA function

enzyme that polymerizes actin to form characteristic comet tails behind the bacterium

• used to propel itself inside and outside of cell → allows quick cell to cell spread (rapid disease progression)

which veterinary species are most susceptible to listeria?

• cows

• small ruminants

• rodents (chinchillas, guinea pigs, rabbits)

(can infect all other animals)

how can listeria be transmitted?

• ingestion of contaminated products and silage

• can enter through exposed mucosal surfaces as ocular mucosa

• vertical transmission

clinical manifestations of listeria

• infection of the brain

• septicemia

• maternal-fetal infection; abortion (usually late-term)

which species does listeria septicemia more commonly affect?

non-ruminants (rare in ruminants → perinatal and juvenile)

pathogenesis of listeria septicemia

• occurs after intestinal breaching: bacteremic phase with hematogenous spread to the viscera (mainly liver and spleen)

• systemic spread → can progress to other organs (brain and placenta)

listeria septicemia clinical signs

• associated with fatal complications such as disseminated intravascular coagulation and multi-organ failure

• organ-specific signs → focal infections after septicemic events (ex. myocarditis, hepatitis, etc.)

placental-fetal listeriosis

• late pregnancy abortion (third trimester) and stillbirth

• mastitis: exclusively in ruminants

how can an animal get cutaneous or ocular listeriosis?

• less frequent

• direct bacterial implantation (bacteremia may be absent)

• eye infection common in ruminants from contaminated silage during feeding (“silage eye”)

  • conjunctival tissue might provide a port of entry in neurolisteriosis

clinical signs of cutaneous/ocular listeriosis

• self-limiting skin dermatitis, cellulitis, and skin abscesses

• listerial keratojunctivitis and uveitis as outbreaks or sporadic cases

what species does neurolisteriosis tend to affect?

• reported in many animals species

• significant problem in domestic ruminants

• low incidence but high fatality

diseases associated with neurolisteriosis in humans and monogastric animals

• meningitis/meningoencephalitis (most frequent)

• brain abscessation

• brainstem encephalitis (rhombencephalitis)

disease associated with neurolisteriosis in ruminants

brainstem encephalitis (rhombencephalitis) is most frequent

proposed routes for neurolisteriosis (2)

1. penetration through mucocutaneous barriers (ex. eye, gut, oral cavity) → centripetal migration to the brainstem (intra-axonally; migrate thorugh neurons)

2. bacteria breach blood-brain barrier or blood-cerebrospinal fluid barrier

clinical signs of rhombencephalitis in ruminants

• circling disease (sporadic or outbreaks)

• incubation period lasting between 2 and 6 weeks

• neurological signs manifest acutely and progress rapidly (especially in small ruminants)

• unilateral brainstem and cranial nerve deficits

• unilateral facial and tongue paralysis

• head tilt and nystagmus

symptoms reflect which cranial nerve nuclei are affected

listeria diagnostic tests

• symptoms are especially important for diagnosis

• cytology, culture, IHC for antibodies on tissue samples; molecular methods

• CSF can be quite variable → isolation from CSF fails in up to 90% of cases

listeria treatment

• if early, responsive to antibiotics (low resistance)

  • symptoms get worse before seeing improvement

• if advanced, animals are usually euthanized

listeria prevention

• no vaccine

• improve silage preparation

• identify source of contamination

is listeria zoonotic?

YES

• foodborne zoonotic potential

• contact with aborted material