Key Microbial agents causing neurological disease 2 Flashcards
What are some features of listeria?
- Gram positive short regular rods
- Facultatively anaerobic
- Differentiation to species level not required - Listeria monocytogenes: Main species of veterinary and human pathogenic interest
Where is listeria found?
- Listeria can be isolated from lots of places
Free living in the environment
Soil. Silage (organisms multiply when pH rises above 5.5), sewage effluent, decaying vegetation, stream water and over 50 different animal species including ruminants, pigs, horses, dogs, cats and various species of birds - Present in animals (and humans) as asymptomatic enteric carriers and are shed in the faeces
- An important source of infection for humans is food, especially soft cheeses, seafood and meat but also vegetables
How is listeria transmitted?
- Exogenous: Ingestion is the primary route
- Endogenous: Septicaemia or spread along trigeminal nerves
How does listeria invade cells?
- Bind to cell wall via internalin
- Escape phagosome with help of haemolysin
- Multiply in cytoplasm with doubling time of 1 hour
- Listeriopods invaginate into adjacent cells allowing entry in a double membraned vacuole
What clinical syndromes are associated with listeriosis?
- Visceral form (septicaemia)
- Abortion
- Neural form
What clinical signs are associated with the neural form of listeriosis?
Neural form presents as meningoencephalitis (circling disease) and is most commonly observed in ruminants with poor quality silage often being tee source.
- Circling in one direction
- Unilateral facial paralysis
- Difficulty swallowing
- Fever
- Blindness
- Keratoconjunctivitis; nystagmus
- Head pressing, head tilt
- Paralysis, recumbency and death
- Sheep and goats can also exhibit star gazing i.e. their heads stretched back due to encapsulated pus in the brain
How does listeria cross the BBB?
Listeria crosses the blood-brain barrier either haematogenously or via nerve cells (trigeminal)
Can animals become immune to listeria?
- Facultative intracellular parasite: Cell mediated immunity is important
- Underlying host immunosuppression especially of the cell mediated immune responses appears to be an important factor in intracellular persistence clinical listeriosis e.g. decreased cellular immunity occurs with advanced pregnancy
How is listeriosis diagnosed?
- Based on clinical signs
- Samples obtained from lesions (blood, placenta, aborted foetal tissues or post mortem tissue specimens inc. CNS) -> gram stain/diff quick where you should see gram +ve short rods but may not be present especially in chronic disease
How is listeriosis treated?
- Penicillin
- most effective in early stages, not effective in chronic cases
- recovery may be accompanied by permanent neurological damge
- Trimethoprim/sulfonamides and rifampin combination has been used in cases of listeriosis in dogs
What signs are associated with feline parvovirus?
- Poor motor control
- Wide based stance
- Incoordination – very clumsy
- Intention tremor
- When asleep = no signs
What can equien herpesvirus 1 cause?
- Late term abortion
- involved in upper respiratory disease
- can cause meningoencephalitis (mutant forms of the virus)
- Horses may present in recumbancy
What is bvoine ephemeral fever?
- Also known as 3 day sickness
- arthropod borne virus of cattle and water buffalo
- enzootic in tropical and subtropical regions of africa, asia, middle east and australia
- epizootics of disease occur when the virus spreads to termperate regions
Describe the pathogenesis of bovine ephemeral fever.
- Virus introduced by arthropod vector (mosquitoes?, midges)
- Vascular inflammatory response (immune mediated?) -> Synovial membranes, muscles, tendon sheaths and skin
- Mineral imbalance (hypocalcaemia)
- Viraemia lasts 4-5 days
What clinical signs are associated with bovine ephemeral fever?
- High morbidity, low mortality (Mortality usually more so to do with recumbency)
- Sudden onset, sudden recovery (72 hours)
- Fever (often biphasic)
- Marked drop in milk production
- Nasal and ocular discharge
- Lameness
- Submandibular oedema
- May see abortion in 2nd trimester