Viruses_wk9(1)

Animal Disease 1: Viral Zoonoses

Characteristics of Viruses:
- Cannot reproduce independently: Viruses require a host cell to replicate.
- Lack independent metabolism: They do not have metabolic processes on their own.
- Non-cellular infectious agents: Unlike bacteria, viruses are acellular.
- Composed of a single type of nucleic acid: This can be either DNA or RNA, surrounded by a protein coat called a capsid.
- Often host-specific: Different viruses target specific host organisms, which can be highly significant in terms of disease transmission and control.

Attachment (Adsorption): Virus binds to specific receptors on the host cell surface.
Entry: The virus or its genetic material enters the host cell.
Uncoating: Viral protein coat is removed, releasing nucleic acids into the host cell.
Replication (Eclipse Phase): The host cell’s machinery is hijacked to produce viral components.
Assembly (Maturation): New viral particles are assembled from the replicated components.
Release: New viruses exit the host cell, often killing it in the process, to infect new cells.

Impacts: Viruses can cause a range of diseases, leading to cell and tissue damage. They can manipulate host cell functions, ultimately affecting the overall health of the organism.
Diagnostics: Techniques may involve tissue or cell culture to identify viral infections, serological tests to detect antibodies, or molecular methods such as PCR to identify viral nucleic acids.

Infection Process:
- Virus enters tissue through saliva from the bite of an infected animal.
- Initial replication occurs in muscle tissue near the bite site.
- The virus moves along the peripheral nervous system to the central nervous system (CNS).
- Upon reaching the brain, it causes fatal encephalitis and can spread to other organs, resulting in multi-organ failure.

Overview:
- Hantavirus is primarily carried by rodents and poses significant health risks to humans.
Transmission: Can occur through inhalation of contaminated droplets, urine, feces, or saliva from infected rodents.
Strains: There are 25 distinct strains, though not all are pathogenic. The disease is distributed worldwide, with varying fatality rates depending on the strain.
Signs & Treatment in Animals vs. Humans:
- Animals usually show no symptoms and do not receive treatment.
- In humans, symptoms include headache, fever, chills, backache, and a petichial rash, with treatment involving antiviral medication and symptomatic care.

Epizootiology:
- Geographic Spread: Present in Africa, Europe, the Middle East, Central Asia, and North America.
Transmission: Primarily spread through the bite of infected mosquitoes; birds act as a reservoir for the virus.
Clinical Signs:
- In animals: Most species are asymptomatic, though some can develop encephalitis, fever, lethargy, weakness, ataxia, and partial paralysis.
- In humans: Symptoms may vary depending on age with risks of severe outcomes such as neurological complications.
Treatment and Management:
- In humans: Focus on symptomatic treatment and managing complications; mosquito control is vital in prevention. Vaccination strategies implemented for horses, with human vaccines under development.

Epizootiological Background:
- Endemic in macaque monkeys, with 70% of captive and wild macaques infected.
Transmission: Occurs via direct (bites, scratches) or indirect (fomites, aerosol) contact.
Clinical Signs: Typically asymptomatic in macaques; however, fatality in humans is high, with systemic symptoms like muscle weakness, paralysis, conjunctivitis, and dysphagia leading to encephalitis, resulting in death in 70% of cases.
Treatment: Animals receive no treatment; for humans, wound decontamination and antiviral therapy such as Acyclovir is essential.

Clinical Signs in Animals: Affects various species, manifesting in high fever, coughing, dyspnea (difficulty breathing), anorexia, and mucoid nasal discharge. Species affected include felines, canines, swine, ferrets, and marine mammals.
Clinical Signs in Humans: Symptoms vary by strain (A, B, C), leading to upper respiratory issues, with more severe signs in immunocompromised individuals.

Overview: Highly contagious; results in rapid disease progression to death in birds; mild respiratory symptoms may occur in humans.
Transmission: Occurs through direct contact with infected bird droppings or respiratory discharges.
Treatment and Control: Only symptomatic therapy is available for humans; strict quarantine measures and surveillance are critical in controlling outbreaks among animals, with vaccination highly recommended.

Affected Animals:
- Primarily affects cattle, sheep, pigs, goats, as well as some species like hedgehogs, rats, and deer.
Clinical Signs in Animals: Features include high fever, formation of blisters on the tongue, feet, teats, and nares, along with hypersalivation.
Clinical Signs in Humans: Humans typically experience malaise, fever, nausea, vomiting, and painful ulcerative lesions in the oral cavity.
Treatment and Management: No effective treatment is available in animals; infected animals are culled to prevent outbreaks. Humans receive symptomatic treatment and antibiotics for potential secondary infections.

Overview: Caused by a virus from the Poxviridae family, known as Orf; it is zoonotic and can be transmitted between sheep and humans.
Transmission: Involves direct and indirect contact with infected lesions and scabs; the virus remains viable for about a month after scab healing.
Clinical Signs: Symptoms develop rapidly, typically within two to three days, presenting as lesions on lips, nares, ears, eyelids, with possible extension to feet.
Treatment: Supportive care is the only management approach, as no specific antiviral therapies are available.

Overview: Includes Eastern (EEE), Western (WEE), and Venezuelan (VEE) encephalitis viruses, found across the Americas.
Transmission: All forms are transmitted via mosquito bites; EEE and WEE have transmission cycles involving mosquitoes and birds, while VEE cycles between mosquitoes and small rodents. Both humans and horses serve as definitive hosts.
Signs: Characteristically neurological, signs may include seizures and ataxia, with EEE resulting in high mortality rates in horse populations.
Management and Control: Vaccines are available for horses against EEE, WEE, and VEE, though no effective vaccine exists for humans, underscoring the necessity for robust mosquito control measures.