this slide is related to the information of prions and its important diseases in veterinary field.

1. Prions and it’s diseases
Dr. Sameer Sankhe
Department of Veterinary Microbiology
Mumbai Veterinary College, Parel, Mumbai - 400012

2. What are Prions ??
 Prions are described as proteinaceous infectious materials
devoid of nucleic acid and exhibit properties, which
distinguish them from both viruses and viriods.
 Prusiner introduced the term prion to this protein infectious
particle.
 Probably most mammalian species develop prion diseases.
 The unique feature of prion diseases, is they mainly affect the
brain tissues mainly grey matter leading to spongiform
change.

3. Diseases caused by prions
 Prion diseases of animals – Scrapie and Bovine Spongiform
Encephalopathy (BSE)
 Prion diseases of humans – Creutzfeldt-Jakob disease (CJD),
Gerstmann-Straussler syndrome (GSS), Alpers syndrome etc

4. Bovine spongiform encephalopathy (BSE)
 Also known as Mad Cow Disease
 It is equivalent to Scrapie in sheep.
 More than 160,000 cattle deaths in United Kingdom due to
this disease in 1997.
 Causative agent = Prions
 Host susceptibility = bovine are naturally susceptible.
 Zoonotic disease.

5. Mode of spread
 Studies have shown that, there is direct correlation between
the occurrence of disease and inclusion of meat and bone
meal supposedly infected with scrapie causing agent.
 Protein concentrates contaminated with sheep scrapie
agent were considered to be the source of infection.
 It was observed that, the stoppage of sheep origin offal as
ruminant feed led to drastic reduction in number of new
cases of BSE.

6. Pathogenesis
 Entry of the causative agent under natural condition
possibly occurs through oral route.
 After entry the causative agent initially localizes in tonsil,
supra pharyngeal and mesenteric lymph nodes and also
intestines.
 Later it is followed by progressive invasion to the CNS
through the differentiated B-cells.

7. Clinical symptoms and lesions
 Main clinical symptoms of this disease are disturbances in
behavior, sensitivity and locomotion.
 Restless, nervous and show increased excitability, salivation
and licking of muzzle.
 Hypersensitive to touch, sound and light, uncoordinated gait,
decrease in body weight and death [usually seen in 1-6
months after showing symptoms.
 Lesions = spongiform degeneration, amyloid deposition and
neuronal vacuolation are pathognomonic, the lesions are
distributed uniformly in the brain stem.

8. Laboratory diagnosis
 The clinical signs confuses with other disease like rabies,
listeriosis and toxicities, hence laboratory confirmation is
must.
 Brain tissue particularly brain stem is choice of sample for
diagnosis.
 Demonstration of prion by electron microscopy and
Western blotting.

9. Control
 BSE is a notifiable disease in many countries.
 Entire herd is slaughtered, if any infected animal is found.
 Ruminants-derived protein should be excluded from
ruminant rations.
 Carcass of infected animals should be incinerated at high
temperatures.
 Buildings and equipment should be decontaminated by
using high concentrations of sodium hypochlorite or
heated strong solutions of sodium hydroxide.

10. Scrapie
 Also known as Rita, trotters, scratchie, shaking etc.
 The disease is seen in different parts of the world such as UK,
USA, Germany, Norway, Poland and few countries of Africa
and Asia.
 Causative agent - prion protein
 Host susceptibility – sheep (natural host) 2-4years of age are
mainly affected, Goats are also susceptible naturally.

11. Modes of spread
 The mode of spread of the causative agent under natural
condition is not clearly understand.
 The agent may spread horizontally from naturally infected
sheep to uninfected animals.
 It is uncertain whether vertical spread of the agent from ewes
to lamb can occur
 Pastures grazed by scrapie affected sheep are suspected to
spread the causative agent.

12. Pathogenesis
 Infection occurs by oral route.
 First appearance of causative agent in infected lambs occur
in tonsils and supra pharyngeal and intestinal lymph nodes.
 In lymph nodes, replication apparently occurs in follicular
dendritic cells.
 After oral exposure it is thought that the portal of entry to
neural tissues is in the duodenum and ileum.
 The agent then spreads through fibres of the autonomic
nervous system to the spinal cord and medulla oblongata.

13. Clinical signs
 The disease has long incubation period
 Characteristic clinical signs of scrapie is intense pruritis,
which may lead to loss of wool.
 Neurological symptoms such as changes in behaviour,
tremor of the head and neck, locomotor incordination that
progresses to recumbence and death.
 Characteristic histopathological lesions are presence of
spongiform degeneration and neuronal vacuolation in
diencephalons, brain stem, cerebellar cortex of the CNS.
 Absence of inflammatory changes of myelin is seen

14. Laboratory diagnosis
 Laboratory confirmation is must, as the clinical signs may be
confused with disease like rabies, listeriosis and pseudorabies.
 Brain tissue at necropsy is material of choice for lab diagnosis.
 Mice inoculation test is done, but it requires long waiting for the
result.
 Detection of prions by Western blotting

15. Prevention and control
 Notifiable disease
 Strict quarantine procedures are implemented
 Slaughter policies are enforced for infected animals.
 A control policy involving flock certification and movement
restrictions is now in place.
 Rearing of genetically resistant sheep is suitable to prevent
the occurrence of the disease.

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