Key Microbial Causes of Sudden Death – Anthrax Flashcards
What are the important control measures following an outbreak of anthrax?
- Carcass disposal
- decontamination
- vaccination
- restriction of movment of both animals and people
What are the 4 broad classifications of sudden death in ruminants?
- Acute infections
- intoxications
- metabolic and nutritional causes
- physical or environemtnal disasters
Should a post mortem be done in a suspected anthrax case?
No
When factors might make you suspect anthrax?
If they die suddenly and have one or more of the following occur:
- Blood oozes from one or more body orifices and sites of predation (e.g. eyes, anus, udder)
- Blood from the carcase does not clot
- There is a history of anthrax at any time on the property
- The property is located within the anthrax belt
- Any rapidly fatal disease of herbivores – rule out anthrax
What is the first thing you do when you suspect anthrax?
Notifiable disease, so notify appropriate people
What does B. anthracis look like?
- ## Large, blunt ended, gram +ve rods, capsulated (lose capsule when cultured)
List the differences between clostridium spp. and B. anthracis.
- Both spore forming gram positive rods
- Bacillus spp. will grow in air, whilse clostridium spp will only grow anaerobically
- B. anthracis have a capsule in vivo (loses this once cultured) while clostridium spp. do not have a capsule
What is this?
B. anthracis with a capsule (in vivo)
When is B. anthracis spore forming?
- Under aerobic conditions
- this is the vegetative state
- central endospores mean that they are highly resistant
Are the spores of B. anthracis resistent? How can they be destroyed?
- Yes, they have central endospores which are highly resistant
- can survive 2-3 decades in dried cultures
- remain viable in siul for >100 years
- freezing has little effects
- Destroyed by: boiling for 30 mins, dry heat at 140C for 3 hours. Chemical disifectants need to be used at high concentrations for a long time
Where is B. anthracis found?
- Survive as spores in animals or animal products and in soil.
How might B. anthracis spores be brought to the surface of the soil?
- Higher risk of heavy rain after drought - flooding
- excavation
- subsidence of earthworms
When do B. anthracis spores germinate?
- Spores germinate & bacteria multiply when exposed to high temperatures, moist conditions & when there is a lack of other soil-living bacteria
How does B. anthracis enter the host?
- Ingestion of spores
- through scratches or wounds
- Inhalation
- mechanical trasnmission with biting insects (rare)
What are the VFs of B. anthracis?
Both the capsule and toxin are required for virulence
- Capsule: resistant to phagocytosis
- Toxin: 3 thermolabile protein antigenic components (protective antigen, oedema factor and lethal factor)
What differences do we see in anthrax infection between ruminants vs pigs and dogs?
- Pigs susceptible to oedema factor while pigs are susceptible
- Sudden death in ruminants, longer timecourse in pigs
- Few spores required to cause disease in ruminants, many spores required to cause disease in pigs
Explain the pathogenesis of B. anthracis in ruminants.
Cows happily grazing but ruminants are the species MOST susceptible to anthrax Ingest spores present in the environment (relatively FEW spores are required to cause disease) enters through abrasions in mucous membranes Initially stays localised & causes little oedema (rel. resistant to Oedema Factor) but then get a build up of toxin invades bloodstream and causes septicaemia (bacteria and toxins) lethal factor comes into play
How does anthrax present in dogs and cats?
The same as in pigs, longer clinicial course, exposure through ingestion of infected meat, oedema factor plays a greater role.
Are horses more or less susceptible to anthrax comparred to cattle and sheep?
Less susceptible, see signs of enteritis and colic or localised oedema.
What are the three forms of disease caused by anthrax in humans?
- Cutaneous form
- pulmonary form
- intestinal form
What risk/protection level is anthrax?
Notifiable disease, protection level 4
How does an anthrax immunochomatographic test (ICT) work?
- hand held “cow-side” test
- Contains capture antibody against anthrax protective antigen & an inbuilt control
- Blood collected and mixed with sample dilution buffer then placed in the sample well - gives a result in about 15 mins
Can you use an ICT test <48 hours after death?
If the sample collected < 48 hours since death, sensitivity close to 100%. If used > 48 hours after death, sensitivity decreases; however, any positive ICT can still be regarded as a true result.
How is a postive ICT test confirmed?
- Blood or aqueous humour sent to the lab
- ear notch sent to lab if blood cant be sampled
- culture (needs to be in a PC3 lab)
How could you diagnose the localised form of anthrax?
- ICT
- Aspirate fluid from the local affected lymph nodes
Is it possible to treat anthrax?
Yes, but needs to be done quickly.
Penicillin is the drug of choice
What are some control measures for anthrax?
- Vaccination
- regulr monitoring
- immediate notification if disease is suspected
- isolation/quaratine
- making and maintaining records to assist in disease tracing
- appropriate disposal of carcasses
How can anthrax be prevented?
- Vaccination: non-envapsulated, avirulent, spore vaccine
- Carcass disposal: do in accordance with AUSVETPLAN
- Host immunity following infection: permanent immunity following infection if the animal survives
What other Bacillus spp. are there? Are they of a concern?
- Bacillyus cereus: causes gangrenous mastitis in cattle. Opportunistic infection
- Other Bacillus spp.: umbiquitous in environment. Usually associated with a contaminated sample if grown in the lab
