Infectious Agents and Prions

Respiratory Syncytial Virus (RSV)

• Paramyxovirus, enveloped with -ve RNA genome

• Causes syncytia formation in cell cultures

• Severe infection mainly in <1 year, elderly, immunocompromised

• Affects lower airways, causing inflammation and necrosis

• Symptoms: cough, wheezing, respiratory distress for 1-3 weeks

• Major hospitalization cause in late Fall to early Spring

• Transmission via asymptomatic older siblings

• Recurrent infections without immunity

• Diagnosis: PCR; Treatment: supportive care

Smallpox (Variola)

• Caused by a large enveloped DNA virus

• Only DNA virus replicating in the cytoplasm

• Acute infection: fever, myalgia, papular and pustular rashes within 1-2 weeks

• Transmitted by respiratory droplets and fomites

• ~30% mortality rate

• Edward Jenner's vaccine in 1798; global eradication declared in 1980

• No human reservoir or asymptomatic carriers; effective global vaccination

Polio Virus

• Enterovirus, naked +ve RNA genome

• Risk of paralytic disease increases with age

• ~90% infections are subclinical

• Severe: flaccid paralysis; some recover, others remain paralyzed

• Clinical pathway includes entry via oropharynx and crossing blood-brain barrier

• Vaccines: Inactivated Polio Vaccine (Salk) in the US; Oral Polio Vaccine (Sabin) globally

Papilloma Virus (HPV)

• Naked DNA virus causing warts and various cancers

• Common STI, can remain latent

• Abnormalities cause cytoplasmic vacuolization, important for cervical cancer screening

• Treatments: laser, cryo, surgical resection; prevention through condom use and vaccination

Prions

• Infectious agents, replicate by inducing normal proteins to misfold

• Resistant to conventional inactivation methods and show no inflammatory response

• Example: Scrapie in sheep, causing neurodegenerative diseases

• TSEs include Creutzfeldt-Jakob Disease in humans and similar conditions in animals

• No specific treatment; prevention reliant on limiting exposure to infective tissues.