Viruses and Prions

RNA Viruses

Picornaviruses

• Poliomyelitis– Fecal-oral and pharyngeal transmission– Attacks NS and can cause paralysis– Vaccine has nearly eradicated the disease in US.

• Hepatitis A– Fecal oral transmission, often through contaminated food

• Enteroviruses cause a variety of diseases including, febrile illnesses, and acute hemorrhagic conjunctivitis, GI diseases

• Rhinoviruses- common colds

Viruses that cause GI diseases

• Rotaviruses (Reoviridae)• Caliciviruses• Norwalk virus• Norwalk-like viruses

• SARS (Severe acute respiratory syndrome– first reported in Asia in February 2003. – In 2003, a total of 8,098 people worldwide became

sick with SARS; of these, 774 died– High fever, headache, myalgia, dry cough, pneumonia – Spread by close contact

• Common cold viruses

Coronavirus

Bunyaviruses

• Hantavirus Pulmonary Syndrome (HPS)– Rodents are reservoir– Virus airborne from rodent feces

• Viral encephalitis• Crimean Congo Hemorrhagic Fever (CCHF)

– Vector borne zoonosis

Togaviruses

• Rubella (German measels)-produces flat pink rash

usually mild, but congenital rubella syndrome can cause sever abnormalities in babies

• Arboviral Encephalitis viruses -Equine encephalitis – EEE (most severe)– WEE– VEE

Orthomyxoviruses: Influenza

• A variety of types (A, B, and C) infect many birds and mammals

• Type A can infect humans and cause pandemics• Transmembrane proteins Hemagglutinin and

Neuraminidase mediate viral attachment and entry• Mutations cause antigenic drift which results in frequent

changes of HA• Genetic reassortments between different Influenza

viruses result in antigenic shift

Pandemic Strain

Avian viruses

Antigenic shifts

Antigenic shifts

Paramyxoviruses

• Respiratory Syncitial Virus– Children under 1 most severely affected– Common, mild in adults

• Mumps- swellings of oral cavity• Measels (rubeolla)- produces raised red rash• Parainfluenza-croup

Arboviral flaviviruses

• West Nile Fever– Emerging disease in US– Relatively mild– Infects many birds and mammals– Culex spp. are vectors

• St. Louis encephalitis (SLE)• Yellow fever- monkeys are reservoir• Dengue fever and DHF (breakbone fever)

Hepatitis C virus

• Flaviviridae family• Hepacivirus genus• Causes liver disease and cancer• Transmitted through blood, IV drugs, body piercing,

tattoos

Rabies Virus

• Transmitted by bite of infected mammals• Virus migrates from PNS to CNS• Inclusion bodies (Negri bodies) found in brain tissue• IFAT of brain tissue • Infects most mammals, susceptibility varies and is

correlated with maintenance• Slow incubation allows for post-infection vaccination

HIV human Immunodeficiency Virus (Retroviridae)

• Viral properties– Envelope– Protein coat– Complex RNA genome– RT and integrase enzymes

• Infection, dissemination through lymphoid organs, clinical latency, expression of HIV, clinical disease, and death

• Progressive antigenic variation in response to host’s immune system

• CD4 T cell depletion leads to immunodeficiency

DNA viruses

Herpesviruses

• Herpesviridae contains several important agents of human disease and NOT all of them are sexually transmitted

• HSV-1 and HSV-2• Varicella-Zoster• Epstein-Barr virus (EBV)

Herpes simplex viruses

• HSV-1 fever blisters• HSV-2 genital herpes• Both viruses can cause either symptoms• Permanent infections, remain latent in spinal nerves and

erupt into lesions at original site of infection• Lesions are progressively less severe

Chicken pox and Shinglesvericella-zoster virus

• Chicken pox (vericella) – virus enters through mucus membranes– Skin lesions appear after 2 weeks starting on scalp

and trunk and moving to other epithelial sites including respiratory, digestive tract or vagina

– Remain in spinal nerves for decades• Shingles (zoster)- eruption of latent virus from peripheral

nerves to dermatomes

Pox viruses• Small pox (variola virus)-

– Enters throat and resp. tract– Infects phagcytic cells and blood cells– Pus-filled vesicles form in mouth and throat then face,

forearms, hands• Cow pox (vaccinia), monkeypox viruses-

– less severe than small pox– antibodies cross reactive with small pox

• Molluscum Contagiosum Virus- – causes painless pearly white tumors –– increasing as an STD can can become inflamed

around genitals

Warts (Papillomas)Papovaviridae

• HPV- human papilloma viruses– Transmitted by direct contact or fomites– Many different types that can infect a variety of

locations including skin, genital, respiratory tracts– Virus infection lasts a lifetime– Can be malignant– Cervical cancer-99% of cases linked to HPV– Warts may be most problematic in

immunocompromised – Warts not always present

Hepatitis B virus

• Hepadnaviridae• One of the most common blood borne pathogens• Causes liver diseases and cancer• Transmitted through blood and sex• Vertical transmission from mother to baby

Prion Diseases

• Mad Cow Disease (BSE)• Scrapie• vCJD• Kuru

Prions

Infectious proteins

Normally found on surface of mammalian cells

Abnormal secondary and tertiary structures

Resistant to heat and radiation

Long ‘incubation’ period

Prion “replication”

Normal protein transformed from helices to beta pleated sheets

BSE