Common Infectious Agents
Virus
Viruses are obligate intracellular organisms. This means that they cannot replicate outside of a host cell. Viruses use the machinery, or organelles, of the host cell to meet their metabolic needs and to build new viruses. Viruses carry either or which is inserted into the nucleus of the host cell. The viral genes are replicated, transcripted and transcribed to make the structural and functional components of new viruses. The host cell fills with viral units until it bursts, freeing millions of viral units to infect neighbouring cells and to spread to distant body parts. A virus can disguise itself by integrating into the host cell, making it hard for the immune system to recognize the virus as a pathogen. Viral infections are treated with antiviral medications and supportive care. Common equine viruses include:
Bacteria
Bacteria are organisms that feed off organic matter. Bacteria can live within a host body or can survive without a host for extended periods of time. Bacteria do not have nuclei but do contain DNA or RNA arranged in rings. Bacteria are categorized as either gram positive (G+) or gram negative (G-) depending on the properties of their cell walls. Most G- bacteria contain endotoxins that are released upon bacterial death and cause disease, while most G+ bacteria have exotoxins in the secretion that coat their cell wall. Some bacteria are aerobic; others are anaerobic, while others can survive in either condition. Some common bacteria that affect the horse include:
Fungi
Fungi are eukaryotic plant-like organisms that can grow on, or in, body tissues. Fungi include a diverse range of structures, from microscopic yeasts and moulds to large structures such as mushrooms. Fungi are classified biased on their methods of reproduction. Fungi acquire nutrients by forming root-like structures called that are capable of removing materials from the host cells. Most fungi reproduce through the formation and dissemination of which can remain viable in harsh conditions for extended periods of time. Many fungi produce chemical compounds that are harmful to plants or animals. These compounds are called mycotoxins and can contribute to the pathogenic nature of certain fungi. Fungi are also beneficial as they produce chemicals that are used in industry and in medicine. Common types of fungus include:
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