I’ve written this article to attract the attention of hunters, game-biologists and other people who are interested in the conservation of wild ungulates in our country. I say about the potential threaten of the deadly disease spread - CWD, Chronic wasting disease of deer.
First time this disease was described for the North America deer. It's one of the form of Transmissible spongiform encephalopathy (TSE), which attacks the nervous system and other organs of animals and leads to a fatal outcome, to the death of a sick animal. We still don’t know how to treat it and there is not vaccine yet.
We are used to think that animal’s and human diseases cause worms. The most dangerous one is trichinosis, the simplest ones are amoebas and other protozoa what goes to piroplasmosis and other bacteria and viruses. CWD is caused by not studied enough protein structures, which are called prions. They are infectious self-replicating proteins which are modified in comparison with the usual protein, and have spatial structure of the molecule. Not only deer suffer from it. The most famous prions diseases are "mad cow disease”, Scrapie, a Kuru disease described for the Furu people of New Guinea, characterized by a commitment to cannibalism. But now we talk about deer disease.
According to currently available data, CWD affects only deer. The last years' researching haven’t confirmed that it affects people or a livestock. But it’s dangerous for deer and moose because it's fatal and spreads very fast. It’s not only because they move actively and live-in herds. There are other objective reasons, connected with the disease specific and how the pathogens of the disease spread. In comparison with other diseases the infection can happen not only when the animal is in the contact with the sick one or when the infected part of dead animals gets into their bodies but when it contacts with their urine, excrement and saliva from infected animals. Pathogens – prions persist for a long time in the environment – on vegetation and in the soil. The experimental data have confirmed that infection can occur not only between individuals of the same species, but also between representatives of different species. The pathogen taken from the whitetail deer and inserted to the wapiti (American red deer subspecies) caused the CWD.
You need to know that sometimes it’s impossible to identify the sick animal. The incubation period can be longer than the quarantine.
This disease is widely spread now among the whitetail and blacktail deer, wapiti and moose in North America. According the data on May, 2015 the disease cases are fixed among wild and semi-free animals in 23 states of USA and two provinces in Canada. These countries have developed the special measures to prevent the spread of the disease. Many European countries take part in the programs of testing for infection of this prions disease and develop measures to prevent its spread.
Special attention is paid to the problem of genetic predisposition to this disease while studying CWD epidemiology. There are several description of gene mutations, for different species. They encode the prion protein and can be connected with the high predisposition or resistance to this disease. Genotyping by these mutations are done for the North America deer and there are data for Scandinavia.
The research, devoted to the potential genetic predisposition/resistance of ungulates of Russia to infection with the disease of chronic wasting of deer Has started in the A.N. Severtsov Institute of Ecology and Evolution. The data, we obtained at the first stage, lead to disappointing conclusions. The analysis of 160 samples, taken from different part of Russia, has showed that all moose from European part of our country, Ural and Siberia are characterized by low resistance to infection of CWD. A small population of moose, inhabited on the northeast (less than 40%), have higher resistance to this disease. All the studied red deer (more than 100) from the European part of Russia are characterized by the low genetic resistance to infection with the disease.
Our researching in this area still go. It’s clear now that red deer and moose, inhabited on the most part of Russia, are not genetically protected from CWD. And we don’t know other ways how to treat it. The importation of deer from the New World is associated with a high risk of spreading CWD among the deer and moose in Russia. The duration of incubation period doesn't allow to identify the sick animals. We know about the negative experience in other countries. The group of deer imported from Canada in 2002 to one of the deer farms in South Korea was infected by CWD. When they realized that one of the individuals was infected it was to late and the only way was to destroy the whole number of deer. It is not necessary to repeat such experiments! The introduction of exotic species, such as whitetail and black tail deer, to the hunting farms of Russia can lead to the to very serious consequences.
Quotes:
A prion is a protein with an abnormal three-dimensional structure that can cause the transformation of a normal cellular protein homologous into a similar one (prion). Prions, appeared as the result of this procedure, can rearrange the normal protein molecules closest to them into prions. A chain reaction is triggered, during which a huge number of incorrectly folded molecules are formed. Prions increase their number in a living organism. They use the functions of host cells and are similar to viruses. Nowadays, prions are the only known infectious agents that reproduce without the participation of nucleic acids (!). The question of whether prions are considered a form of life is currently open.
All known prions form amyloid (protein aggregates).
The incubation period of prion disease is determined by the rate of exponential growth of the number of prions. It depends on the rate of linear growth and fragmentation of aggregates. The initial presence of a normally stacked cell protein, which corresponds to the prion protein is necessary for prion reproduction. The organisms with the lack the normal form of prion protein do not suffer from prion diseases.
The prion form of the protein is extremely stable and accumulates in the affected tissue, causing its damage and die off. The stable prion form means that they are resistant to destruction by chemical and physical agents, so it is extremely difficult to destroy these particles or restrain their growth. There are several prion forms (strains), each with a slightly different structure.
Prions cause the next diseases: transmissible spongiform encephalopathies (TSE) of various mammals, including bovine spongiform encephalopathy ("mad cow disease"). In humans, prions cause Creutzfeldt-Jakob disease, a variant of Creutzfeldt-Jakob disease (vCJD), Gerstmann-Straussler-Scheinker syndrome, fatal familial insomnia, and kura. All known prion diseases affect the brain and other nerve tissues, are currently incurable and ultimately fatal.
The importation of exotic species such as whitetail and black tail deer to the hunting farms of Russia from Canada and USA can lead to to almost total extinction of Russian deer and moose within a few years.
Marina Kholodova, Doctor of Biological Sciences, Chief Researcher, Head of the Cabinet of Methods of Molecular Diagnostics of IPEE RAS
