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Viruses are important pathogens of livestock. Diseases such as foot-and-mouth disease and bluetongue are caused by viruses. [176] Companion animals such as cats, dogs, and horses, if not vaccinated, are susceptible to serious viral infections. Canine parvovirus is caused by a small DNA virus and infections are often fatal in pups. [177]
A viral disease (or viral infection) occurs when an organism's body is invaded by pathogenic viruses, and infectious virus particles (virions) attach to and enter susceptible cells. [ 1 ] Examples include the common cold , gastroenteritis , COVID-19 , the flu , and rabies .
Gamma phage, an example of virus particles (visualised by electron microscopy) Virology is the scientific study of biological viruses.It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they ...
A virus with this "viral envelope" uses it—along with specific receptors—to enter a new host cell. Viruses vary in shape from the simple helical and icosahedral to more complex structures. Viruses range in size from 20 to 300 nanometres; it would take 33,000 to 500,000 of them, side by side, to stretch to 1 centimetre (0.4 in).
An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection. Infections can be caused by a wide range of pathogens, most prominently bacteria and viruses. [2] Hosts can fight infections using their immune systems.
Also called silent disease, silent stage, or asymptomatic disease. This is a stage in some diseases before the symptoms are first noted. [23] Terminal phase If a person will die soon from a disease, regardless of whether that disease typically causes death, then the stage between the earlier disease process and active dying is the terminal phase.
Viral disease is the sum of the effects of viral replication on the host and the host's subsequent immune response against the virus. [3] Viruses are able to initiate infection, disperse throughout the body, and replicate due to specific virulence factors. [2] There are several factors that affect pathogenesis.
HIV was a zoonotic disease transmitted to humans in the early part of the 20th century, though it has now evolved into a separate human-only disease. [36] Some strains of bird flu and swine flu are zoonoses; these viruses occasionally recombine with human strains of the flu and can cause pandemics such as the 1918 Spanish flu or the 2009 swine ...