Transmissible spongiform encephalopathies (TSEs) are progressive neurodegenerative diseases caused by abnormally folded proteins, called prion, these diseases are collectively called prion diseases since they all involve the accumulation in the brain of the infectious protein and cause the characteristic symptoms of the disease, leaving the brain of their victims like a sponge under the microscope, and all are fatal, they are rare in both humans and animals.
Transmissible spongiform encephalopathies include bovine spongiform encephalopathy (BSE or “mad cow disease” in cattle), chronic wasting disease in cervids such as deer and elk, scrapie in sheep and goats, transmissible mink encephalopathy, and spongiform encephalopathy of exotic ruminants, all seem to be related.
Bovine spongiform encephalopathy (BSE)
Bovine spongiform encephalopathy, commonly known asmad cow disease”, is a fatal degenerative brain disease of cattle caused by an abnormal protein, it is one of many transmissible spongiform encephalopathies that affect different species of mammals.
The first BSE outbreak occurred in the United Kingdom in 1986 and caused a major food shortage that lasted for years, since then there have been several more cases of BSE in several countries around the world and most of those affected have died, there is no cure or preventive treatment for BSE and the incubation period of the disease can last from two to eight years.
Scientists have discovered that an abnormal form of the prion protein, called PrPSc, causes the neurological disease in animals affected by BSE. The abnormal prion protein is also found in other types of transmissible spongiform encephalopathies, including scrapie in sheep and goats; chronic wasting disease in cervids and vCJD in humans; There is currently no scientific evidence that any other type of transmissible spongiform encephalopathies in animals can be transmitted to humans.
In animals affected by BSE, a series of clinical signs develop, such as tremors and muscle weakness and the animal gradually loses coordination until it dies. Affected animals do not show appetite and their meat may appear to be rotting. Initially, the symptoms of BSE are similar to those of scrapie, so it was originally thought that BSE could be a new variant of that disease.
To prevent BSE, the United States has taken a multipronged approach that includes testing feed for the disease and banning certain parts of beef that have been shown to pose a high risk, and the FDA bans meat reprocessing. vaccine that may contain the TSE agent and also does not allow parts of any animal that may be infected with BSE to be used in cow feed.
Chronic Wasting Disease (CWD)
The chronic wasting disease It is a fatal brain disease of cervids (deer and elk), like BSE, it belongs to a family of diseases known as transmissible spongiform encephalopathies, the causative agent of these diseases is an infectious protein called prion.
Prions in transmissible spongiform encephalopathies are infectious because they cause normal proteins found primarily in nerve cells in the brain to misfold into an abnormally structured shape that eventually kills these cells. These misfolded proteins are then removed from the surface. cellular and are ingested by other cells, causing them to also adopt the distorted shape, this process is believed to be what causes the characteristic symptoms of transmissible spongiform encephalopathies, such as drastic weight loss, lack of coordination and excessive drooling (of there the term emaciation).
CWD can be transmitted from one animal to another by direct contact or through contaminated water or feed. It has been shown to spread within herds and between animals in captivity and in the wild by contact, but it has not yet been transmitted between species. or from mother to offspring, it can also be transmitted through environmental contamination, such as decomposing corpses or contaminated soil.
The first signs of CWD are non-specific and include a change in behavior, weight loss and loss of coordination (tremors), as the disease progresses, it causes more severe behavioral changes, ataxia, lack of muscle control, difficulty swallow, causing aspiration pneumonia and death, the incubation period is long and varies from animal to animal, and some animals die without showing any symptoms.
There is no treatment or vaccine for CWD and it is considered a disease that occurs naturally in cervid populations. Although the exact mechanism is unknown, infection can be confirmed by immunohistochemistry and/or Western blot, which detect protease-resistant PrPSc in the brain or other tissues of affected cervids.
Unlike BSE, which can be detected by analyzing beef samples, the detection of CWD requires direct examination of brain tissue, for this reason, the only way to confirm an infection is to perform a post-mortem examination of the animal, The presence of the prion is usually confirmed by the presence of spongiform changes in the brain and by the finding of protease-resistant PrPSc.
scrapie
Several diseases that affect sheep and goats are known as scrapie, scrapie or transmissible spongiform encephalopathies (TSE), these diseases are progressive and always fatal, they are also known as spongiform encephalopathies because a sponge-like pattern is observed in the brain tissue of infected animals.
In many transmissible spongiform encephalopathies, a genetic component is evident, but the exact mechanisms that cause them to develop are unknown. The abnormal proteins that cause the diseases have a very long incubation period, do not respond to heat or radiation, and do not generate any detectable immune response, these proteins also cause other proteins to take an abnormal shape and reproduce, resulting in a chain reaction that ultimately destroys nerve cells in the brain.
The disease is believed to be transmitted by ingesting contaminated meat or bone meal in livestock feed, the emergence of BSE (also known as mad cow disease) in 1985 has been linked to changes in farming practices. extraction of corpses and livestock waste that allowed infectious material to be added to animal feed.
After an incubation period of 18 months or more, affected animals begin to show signs that vary from animal to animal; these typically include behavioral changes, head and neck tremors, and itching, which animals can relieve by rubbing against objects. fixed, the signs of the disease progress to lack of locomotor coordination and recumbency, followed by death.
Infections of the brain with the scrapie agent can be detected by examining biopsy samples of the lymph nodes and medulla oblongata with IHC, certain haplotypes in sheep confer natural genetic resistance to scrapie.
Feline transmissible spongiform encephalopathies (FES)
FSE is also part of the transmissible spongiform encephalopathies and is a fatal neurodegenerative disease that affects domestic and captive felines. The disease is believed to be caused by the ingestion of contaminated meat from other animals infected with BSE (also known as BSE disease). mad cows), FSE was first diagnosed in a Siamese cat at the Bristol Veterinary School in England in 1995, subsequently found in pumas, cheetahs, tigers and wildcats in UK zoos.
FSE is similar to but appears to be distinct from the human prion disease, new variant Creutzfeldt-Jakob (vCJD), the disease progresses more rapidly in the cat than most transmissible spongiform encephalopathies and death occurs between 6 and 8 weeks after the onset of symptoms, clinical signs of the disease include behavioral changes, unsteady gait and incoordination, difficulty walking, excessive salivation and dilated pupils, in the later stages of the disease the cat becomes aggressive and He may wander around the house or hide in a corner.
Histopathological lesions of the brain in 2 cases of EEF consist of severe diffuse vacuolation of the gray matter neuropil and gliosis, neuronal perikarya are also affected, resulting in intracytoplasmic vacuolation, intense immunostaining with PrPsc is observed in brain sections, especially in the cerebral cortex and cerebellum, in these two cases of EEF, the infectious agent was deposited in the central nervous system (CNS).
