Chapter 13.5 Microbiology: Animal Viruses and Prions

Animal virus classifications

family, genus, species

Animal virus family

name ends in -viridae based on genome, virus strcuture, and envelope

Animal virus genus

name ends in -virus (Eternovirus, Coronavirus)

Animal virus species

name usually derived from the disease which caused it: poliovirus, ebola virus, influenza virus

Steps of animal virus replication

targeting for replication sites, attachment, penetration, uncoating

Uncoating

release of nucleic acid from nucleocapsid

Ways enveloped animal viruses enter host cells

fusion or endocytosis

Ways naked viruses enter host cells

endocytosis

Steps of fusion

absorption, membrane fusion, nucleocapsid released into cytoplasm, uncoating (pushes through the host cell surface)

Steps of endocytosis

absorption, endocytosis, release from vesicle, uncoating (host cell surrounds phage and takes it into the cell)

Shedding a virus

virus exsits from the host usually through the same spot it entered from

How is shedding diffrent from transmission?

shedding is leaving an old cell while transmission is entry into a new cell

Main characteristics of bacteriophage lytic replication

no fusion occurs, only nucleic acids enter the host cell, targeting is unecessary, activity occurs on the surface of the cell, replication depends on if DNA or RNA and single or double strands are present, lyses the host cell to escape

Main characteristics of animal virus replication

fusion is common, entire virus enters the cell, targeting is needed, activity takes place inside the cell, replication phage occurs always, budding is used to exit the host cell

Acute animal infection

short duration (days to months), infected cells die, virus sheds during infection, immunity usually occurs

Steps of an acute animal infection

incubation, prodromal (symptoms begin), illness, decline, convalescent (recovery)

Persistant animal infection

virus which is continually present and released (latent and chronic infections)

Latent infection

Persistent infection with recurrent symptoms that "come and go"

Chronic infection

incubation, prodromal, illness (never declines)

Hepatitis A, B, C

chronic infection which leads to liver failure

Cold sores (herpes)

spreads through the trigeminal neuron as a episome where it lays dormany until activated

Tumor (neoplasm)

swelling caused by abnormal cell growth

Benign tumor

tumor which remains confinded in one region (localized)

Malignant tumor

tumor which spreads to other parts of the body (respiratory and lymphatic systems)

What is the cause of tumors?

non-function or malfunction of cell growth contols (proto-oncogenes)

Viral trasnformation of cells

a process where a virus alters the genetic makeup of a host cell (retrovirus)

Retrovirus

RNA viruses that become proviruses when they infect cells

Provirus

viral DNA that inserts into a host genome

What enzyme allows retoviruses to convert RNA to DNA?

reverse transcriptase

How do retroviruses transform cells?

causes growth patterns to drastically change

What determines the host range for a given virus?

defined by virus ligand/host cell receptor

What can result from more than one type of virus infects the same host cell simultaneously?

antigenic shift where viruses exchange genetic information

What does a genetic shift in viruses mean?

aquire new hemagglutinin (HA) gene gaining the ability to infect more varied hosts

What does a genetic drift in viruses mean?

hemagglutinin (HA) gene mutates which makes viruses adaptable to host cell changes

What is the consequences of a genetic shift and drift?

causes hosts to be less immune to viruses meaning we have to get more shots to prevent immunocompromization

Prions

infectious particles composed of only proteins

What diseases are caused by prions?

cause TSE's (Mad cow disease, Kuru, Scrapie, Creutzfeldt-Jacob disease)

Charcteristics of prions

heat resistant, chemical resistant, 100% fatal to host cells, kills within months or several years, targets the brain and breaks it down

What causes hosts to aquire prions?

consumption of prions, handleing of contaminated items, mutated CNS genes can result in herditary prions

Steps of prion replication

prions link with normal proteins and convert them to prions overtime turning all proteins into prions killing the host