Bovine Spongiform Encephalopathy in Cattle

Bovine Spongiform Encephalopathy in Cattle

1. Bovine Spongiform Encephalopathy (BSE) Mad Cow Disease

2. Introduction Bovine spongiform encephalopathy (BSE) is a progressive, fatal, infectious neurologic disease that is due to the accumulation of misfolded proteins, termed prions, in the central nervous system of cattle.  BSE causes progressive neurologic signs such as ataxia and hyperesthesia and is always fatal. There are no known vaccines or treatments to control the disease. Confirmatory diagnosis is based on postmortem detection of misfolded prion proteins in the brain. BSE is a zoonotic disease, causing variant Creutzfeldt-Jakob disease ( vCJD ) in humans . Prions are also the cause of  scrapie  of sheep and goats;  chronic wasting disease  of deer;  transmissible mink encephalopathy

3. Etiology

4. Transmission Classical BSE develops as a result of foodborne exposure  to prions via contaminated animal-source proteins (meat and bone meal) in cattle rations. Calves born to infected cows are at greater risk of acquiring BSE than are calves born to non-infected cows; however, this mode of transmission is of minor importance relative to infections acquired through contaminated feed sources.  BSE is not transmitted horizontally  by contact or aerosols . Atypical form is naturally and sporadically occurring and older cattle are affected.

5. Host Most cases of classical BSE are diagnosed in cattle 3–6 years old.

6. Clinical signs Classical BSE The incubation period after exposure is 2–8 years Initial clinical signs of BSE are hyperesthesia ,  nervousness , Fear reluctance to be milked,  Terminal stage Excitation aggression  toward either farm personnel or other animals, low head carriage, ataxia, and tremors. Muscle fasciculation Weight loss and decreased milk production are common. Most animals reach a terminal state by 3 months after clinical onset. Morbidity: 2-3 % Mortality: 100 %

7. Diagnosis Detection of the causative agent ( PrP Sc ) in brain samples by:    ELISA Western blotting techniques Immunohistochemical techniques Rapid Tests PM examination Spongiform changes in gray matter.

8. Prevention and Control Targeted surveillance of bovines that show signs on the clinical spectrum of BSE ; transparency in reporting findings of BSE; safeguards on importation of relevant commodities; removal of tissues with the greatest infectivity (brain, spinal column, etc.) during slaughter and processing of carcasses and from the human food and the animal feed chains; prohibition of the inclusion of tissues with the greatest infectivity in animal feeds, thus removing potentially contaminated material from the food chain; humane destruction of all suspected animals exposed to feed contaminated with BES agent(s); banning the use of ruminant-derived protein meal (ruminant-to-ruminant feed ban, further reinforced by a mammalian-to-ruminant feed ban); appropriate disposal of carcasses and all animal products; and livestock identification to enable effective surveillance and tracing of suspected livestock.