Animal prion diseases
Two key nosological entities affecting farm animals are of veterinary and epidemiological significance. These diseases cause colossal economic damage and pose a potential epidemiological threat.
Scrapie (Scrapie) This disease affects sheep and goats. The name comes from the English verb to scrape, which accurately reflects the common folk name of the infection — "the itch". The clinical picture consists of a characteristic triad of symptoms:
- Severe skin itching.
- Severe CNS involvement manifested by coordination disorders.
- Steadily progressive course.
The outcome of the disease is always the same — inevitable death of the infected animal.
Bovine spongiform encephalopathy (BSE) Is widely known due to a major epidemic outbreak in the UK in 1992–1993, which later spread throughout Europe. The incubation period of the disease is enormous, lasting from 1.5 to 15 years. Transmission occurs via the alimentary route. The main transmission factor was meat-and-bone meal made from the carcasses of infected animals and added to feed. The maximum concentration of pathogenic prions in the animal's body is localized in the brain and spinal cord tissues, as well as in the eyeballs. Clinically, BSE presents with severe CNS damage, pronounced ataxia, and always ends in a fatal outcome.
Microbiological diagnostics
Due to the absence of a classic immune response of the organism to prions, disease diagnosis is based on a combination of pathomorphological and modern immunochemical methods.
Pathohistological examination Serves as the absolute "gold standard" for diagnosing prion diseases. When studying brain tissues, the pathologist relies on the following markers:
- Detection of specific spongiform changes in the tissue.
- Presence of astrocytosis (pronounced gliosis).
- Positive staining for amyloid.
Crucial differential diagnostic sign: inflammatory infiltrates are completely absent in the affected tissues, which is uncharacteristic of bacterial or viral encephalitis.
Immunochemical and genetic methods For intravital or confirmatory diagnosis, cerebrospinal fluid (CSF) is analyzed. Using ELISA (enzyme-linked immunosorbent assay) and Western blotting (WB) with monoclonal antibodies, protein markers of brain damage are detected. Molecular genetic methods are also actively used: PCR for precise detection of the PrP protein and deep genetic analysis of the animal's prion gene.
Prevention and disinfection regimens
Prions possess extremely high resistance in the external environment; therefore, standard decontamination regimens against them are completely ineffective. The complex of measures is divided into two large groups.
Restrictive measures Strict bans have been introduced in medical and manufacturing practice:
- Restriction or complete ban on the use of medicinal products of animal origin.
- Complete cessation of the production of pituitary hormones obtained from animals.
- Strict restrictions on dura mater transplantation.
When contacting any biological fluids, the use of thick rubber gloves is a mandatory safety requirement.
Specific disinfection and sterilization Decontamination of instruments and contaminated environments requires extremely harsh conditions:
- Autoclaving: performed at a temperature of 134 °C for at least 30 minutes. An alternative regimen is 121 °C for 4 hours, but with the mandatory addition of 1N sodium hydroxide (NaOH) solution.
- Chemical treatment: an aggressive mixture of bleach and 1N NaOH with an exposure time of at least 1 hour is used.
- Physical method: complete incineration remains the most reliable method for disposing of contaminated materials.
Briefly: answers to topical questions
What nosological forms of human prion diseases are distinguished in modern medical classification?
The following nosological forms of human prion diseases are distinguished:
- Kuru disease.
- Creutzfeldt-Jakob disease — sporadic, familial, iatrogenic, and "new" variants are described.
- Gerstmann-Sträussler-Scheinker syndrome — an exceptionally rare familial disease.
- Fatal familial insomnia — a genetically determined prion disease.
- Amyotrophic leukospongiosis.
Sources also describe conditions with changes analogous to prion diseases or prion-associated inclusions:
- Alpers' disease — a chronic progressive encephalopathy with liver involvement.
- Spongiform myositis with prion-associated inclusions — a disease in which inclusions containing prion proteins are detected in muscle tissue.
What is the molecular mechanism of the transformation of the normal cellular protein PrPc into the pathogenic isoform PrPSc?
The molecular mechanism of the transformation of the normal protein into the pathogenic isoform is not fully understood and consists of a change in its conformation.
It is known that the pathogenesis is based on the following processes:
- Conformational change of the normal protein under the influence of external factors.
- Conversion of the normal prion protein into the pathological one (PrP-Sc).
- Accumulation of mutant forms in brain tissues that are resistant to proteolysis.
- Neuronal death due to the development of gliosis and vacuolization.
These conformational rearrangements allow prion infections to be classified as conformational diseases.
What are the main routes of transmission of prion infections in the human population?
The main routes of transmission of prion infections in the human population include alimentary, iatrogenic, and hereditary mechanisms.
The following routes of infection are distinguished:
- Alimentary route — consumption of infected animal products and food supplements derived from raw cattle organs.
- Artificial (iatrogenic) route — transmission via medical procedures. Includes blood transfusion, transplantation (corneal transplantation), medical route (administration of growth hormone), and instrumental route (use of insufficiently processed surgical instruments).
- Hereditary route — transmission of the disease in an autosomal dominant manner.
To memorize the histological picture, use the acronym GAV (in Russian): Gubkoobraznye izmeneniya (Spongiform changes), Astrotsitoz i Amiloid (Astrocytosis and Amyloid), Vospaleniya net (No inflammation/infiltrates).
Class and exam questions
Prions are a modified form of the body's own proteins; therefore, they are not recognized by the immune system as foreign agents, and neither inflammatory infiltrates nor classical antibodies are formed.
Prions do not induce a classical immune response in the body.
What is the main danger of BSE for humans?
The epidemiological danger lies in the possibility of alimentary transmission of the agent through the consumption of contaminated meat and, especially, nervous system tissues (brain, eyes) of sick cows.
How to properly sterilize surgical instruments after contact with prions?
Regular boiling or standard autoclaving will not help. Harsh autoclaving at 134 °C for 30 minutes or chemical treatment with sodium hydroxide combined with bleach is required.
What else to study on this topic
- Structural features and spatial conformation of normal and pathological prion proteins (PrP)
- Detailed analysis of epidemiological chains during the outbreak in the UK (1992–1993)
- Immunoblotting technique for prion detection in cerebrospinal fluid
- Economic consequences of restrictive measures in animal husbandry and pharmacology
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