7: viral infections

virion

individual virus particles; contain genetic material as either DNA or RNA, and only a small number of genes in their genome; incapable of metabolism or reproduction

prion

misfolded proteins, containing no nucleic acid; causes holes in the brain and common in animals

viral tropism

the specific affinity of a virus for a particular host cell; detemines which cells the virus can infect and replicate in

adsorption, penetration, duplication, assembly, release

steps of viral replication

adsorption

binding of the virus on cell surface

penetration

viral passage through cell membrane

lysogenic cycle

viral genome is inserted into host genome; viral genome copies into every new cell that replicates; remains in latent state until permissive conditions occur

lytic cycle

viruese direct the cell to synthesize new viral capsid proteins and copy the viral genome; new viruses form in cytoplasm and erupt from host cell

budding

virus froms vesicles to exit host cell; process disrupts host cell membrane, causing leakage and osmotic shock; often kills host cell

chronic infections

virus is detectable in tissue samples, multiplying at slow rate; symptoms mild or absent

latent infections

virus enters dormant phase; generally not detectable and no symptoms; can reactivate and result in recurrent infections

oncogenic

viruses that casue neoplasia

teratogenic

viruses that cross placenta and cause developmental disturbances and permanent defects

poxivirus, herpesvirus, hepadnavirus

enveloped DNA viruses

poxiviruses

produces eruptive skin pustules that leave scars; largest and most complex animal virus, having the largest genome of all viruses; multiplies in cytoplasm

smallpox

type of poxivirus; first disease to be eliminated by vaccination; exposure through inhalation or skin contact; infection associates with fever, malaise, prostration, rash

disseminated intravascular coagulation

DIC; when coagulation systems becomes too stimulated, resulting in small clots all over body and no coagulation left in the rest of the blood; paradoxical result of bleeding out

molluscum contagiosum

type of poxivirus; primarily infection of children or STD; lesions are small, smooth macules in genital area and thighs; treatments include freezing, electric cautery, chemical agents

herpesvirus

characterized by latency and recurrent infection; genome replicates within nucleus; transmitted through direct mucosal or skin contact or airborne

herpes simplex virus

HSV; type of herpes virus; humans are susceptible to HSV-1, leading to lesions on oropharynx, cold sores, fever blisters, or HSV-2, leading to lesions on genitalia, possibly oral

herpes labialis

HSV-1 infection; fever blisters, cold sores; most common form of recurrent infection; vesicles around lips; itching/tingling; lesion crusts over in 2-3 days and heals

herpetic gingivostomatitis

HSV-1 infection; infects oropharynx in young children; results in fever, sore throat, swollen lymph nodes

herpetic keratitis

HSV-1 infection; occular inflammation; results in conjunctivitis,sharp pain, sensitivity to light

genital herpes

HSV-2 infection; starts with malaise, anorexia, fever, bilateral swelling and tenderness of groin; clusters of sensitive vesicles on genitalia, perineum, and butt; urethritis, painful urination, cervicitis, itching; ulceration of vesicles

HSV infection in newborn

HSV 1 and 2 can infect fetus and neonate; potentially fatal; transmission either by mother before or after birth; infection can occur in mouth, skin, eyes, CNS

diagnosis of HSV

signs of vesicles and exudate; scrapings from base of leisions showing giant cells, culture and specific tests for diagnosing severe or disseminated HSV; direct fluorescent antibody tests

treatment of HSV

use acyclovir, famciclovir, valacyclovir, or topical medications

varicella-zoster virus

VZV (HSV-3); causes chickenpox and shingles; targets resp mucosa and skin

chickenpox

VZV infection; results in mild illness, and highly contagious in children; may take up to 2-3 weeks for infection to generate clinical manifestation; complications may be severe in immunocompromised hosts

shingles

recurrence of VZV infection when virus emerges from latency, usually in adults who were exposed and infected in childhood; characterized by belt of skin area of painful rash with blisters

cytomegalovirus

CMV (HHV-5); presence of giant cells with nuclear and cytoplasmic inclusions; transmitted in fluids; most infections are asymptomatic, virus may be latent; targets salivary epithelia and visceral mucosa

epstein-barr virus

EBV (HHV-4); resides in human lymphoid tissue and salivary glands and is spread by direct oral contact and contamination with saliva and other body fluids; cause of infectious mononucleosis and closely associated with neoplastic transformation of target cells

burkitt lymphoma

b cell malignancy caused by EBV; usually develops in jaw and grossly swells the cheek; occurs in central african children 4-8 yrs, may be associated with chronic coinfections with malaria

nasopharyngeal carcinoma

malignancy of epithelial cella caused by EBV; occurs in older chinese and african men

diagnosis of EBV

differential blood count showing lymphocytosis, neutropenia, and large atypical lymphocytes; serological assays to detect antibodies and antigen

treatment of EBV

directed at relief of symptoms of fever and sore throat; disseminated disease may be treated with IV gamma globulin, interferon, acyclovir, and monoclonal antibodies

human herpes virus 6

HHV-6; human t-lymphotropic virse, transmitted by close contact with saliva and other secretions; causes roseola in babies 2-12 months; mono-like symptoms in adults, lymphadenopathy and hepatitis

hepadnaviruses

DNA viruses primarily found in humans, primates, and birds; most significant in humans is orthohepadnaviruses which includes the important disease causing agents of hepatitis B

hepatitus B virus

HBV; multiplies only in liver; transmitted by blood, semen, and vaginal secretions; may become chronic; may result in liver necrosis, cirrhosis, hepatocellular carcinoma

pathogenesis of HBV

virus reaches liver, multiplies and releases more virus into blood; many will have mild symptoms: malaise, fever, chills, anorexia, abdominal discomfort, diarrhea; some progress to chronic liver disease

diagnosis of HBV

based on examination of risk factors, serological tests to detect viral antibodies or antigen; screening of blood, semen, and organs for any banks; routine prenatal testing for pregant women

management of HBV

mild cases managed by treatment of symptoms and supportive care; chronic infections treated with interferon

prevention of HBV

vaccination for high risk individuals and encouraged for all newborns and infants

adenovirus, papovavirus, parvovirus

nonenveloped DNA viruses

adenovirus

common DNA viruses that are passed in humans by contact with secretions, contaminated objects, or airborne droplets; usually infect resp and intestinal epithelia, and conjunctiva; some remain latent

adenovirus infection

common in children and cause fever, acute rhinitis, pharyngitis, cough, otitis media, enlarged lymph nodes, follicular lesions of conjunctiva; cause severe resp disease in immunocompromised people

human papillomavirus

HPV; type of papovavirus; cause of plantar and genital warts; 9 types inc risk for reproductive cancer; 2 types account for mpst metastatic tumours; early detection through inspection

orthomyxovirus

influenza virus; 4 subtypes of A, B, C, D; contains lipoprotein envelope and glycoprotein spikes; transmitted via aerosols and fomites, easily passed in crowded places

hemagglutinin

type of glycoprotien spikes found on influenza virus; has 15 different subtypes; most important virulence factor; binds to host cells

neurominidase

type of glycoprotien spikes found on influenza virus; has 9 subtypes; hydrolyzes mucus and assists viral budding and release

antigenic drift

constant mutation of virus;one gene or RNA strands is substitued with a gene or strand from another influenza virus from different animal host

influenza A

causes acute, highly contagious resp illness; resp transmission, binding to cilicated cells of resp mucosa; causes rapid shedding of cells, stripping respiratory epithelium and causing severe inflammation; weakened host defenses predispose people to secondary bacterial infections, esp pneumonia

influenza B

not known to undergo antigenic shift

influenza C

known to cause only minor resp disease; probably not involved in epidemics

paramyxovirus

includes several important human pathogens: morbillovirus, mumps virus, and resp syncytial virus; generally transmitted to resp tract by resp aerosol, causing resp symptoms

mumps virus

type of paramyxovirus; associated with swelling of parotid salivary glands; incubation 2-3 weeks fever, muscle pain and malaise, swelling of one or both cheeks

morbillovirus

type of paramyxovirus; causes measles; highly contagious and transmitted via resp aerosols; causes sore throat, dry cough, headaceh, conjunctivitis, lymphadentitis, fever, oral lesions; rarely leads to serious complication - sclerosing panencephalitis

respiratory syncytial virus

RSV and also called pneumovirus; infects upper resp tract and produces giant multinucleate cells; children 6 mo or younger most susceptible; causes fever, rhinitis, wheezing, otitis, croup

rhabdovirus

rabies virus; slow, progressive zoonotic disease; can be spread by both wild and domestic mammals by botes, scratches, inhalation of droplets

rabies

virus enters through bite and enters nerve endings and migrates towards ganglia, spinal cord and brain; virus follows CN V to release in salivary glands; may result in fever, nausea, vomiting headache, fatigue

coronavirus

large RNA viruses with distincively spaced spikes on envelopes; common in domesticated animals; 3 classifications: HCV causes cold, enteric virus, and resp viruses

severe acute respiratory syndrome

SARS; transmitted by droplet or direct contact; causes fever, body aches, malaise; may or may not have resp symptoms with breathing problems; severe cases may result in death

rubella

german measles cause by rubivirus; transmitted through contact with resp secretions; has 2 clinical forms including postnatal rubella and congenital rubella

postnatal rubella

type of rubella; causes malaise, fever, sore throat, lymphadenopathy, rash; generally mild, lasting about 3 days

congenital rubella

type of rubella; infection during 1st trimester most likely to induce miscarriage or multiple defects

hepatitis C virus

HCV; flavivirus aquired through blood contact; possible to have severe symptoms without permanent liver damage, chronic liver disease more common; cancer may result from chronic infection

arbovirus

viruses spread by arthropod vectors including mosquitoes, ticks, flies, gnats; most cause mild fevers; some mat cause severe encephalitis and life-thratening hemorragic fever

viral encephalitis

caused by aborvirus; involves brain, meninges, and spinal cord; convulsions, tremor, paralysis, loss of coordination, memory deficits, changes in speech and personality, coma; survivors may experience permanent brain damage

yellow fever

type of hemorrhagic arbovirus fever; urban cycle: humans and mosquitoes; sylvan cycle: forest monkeys and mosquitoes; may progress to oral hemorrhage, nosebleed, vomiting, jaundice, liver and kidney damage

dengue fever

type of hemorragic arbovirus fever; flavivirus carried by aedes mosquito; usually mild infection; may be fatal in causing dengue hemorrhagic shock syndrome, breakbone fever, extreme muscle and joint pain

human immunodeficiency virus

HIV; enters through mucous membrane or skin and travels to dentritic phagocytes under epithelium; attaches to CD4 receptor and fuses with cell membrane; viral DNA is integrated into host chromosome; may produce lytic infection or remain latent

primary effects of HIV

extreme leukopenia, esp lymphocytes; formation of giant T cells and other syncytia, allows virus to spread from cell to cell; infected macrophages release virus in CNS with toxic effect → inflammation

secondary effects of HIV

destruction of CD4 lymphocytes which allows for opportunistic infections and malignancies

HIV signs and symptoms

directly related to viral blood level and level of T cells; initially has mononucleus-like symptoms that soon disappear; destroys immune system

AIDS diagnosis

when person is positive for HIV; when they have low CD4 (fewer than 200 cells/mL if blood or fewer than 14% of all lymphocytes) or when they experience one or more of a CDC-provided list

HIV diagnosis

based on detection of antibodies specific to the virus in serum or other fluids; initial screening consists of latex agglutination and rapid antibody tests; followed up with western blot analysis to rule out false positives

pre-exposure prophylaxis

tx of prophylactic HIV; for people who are HIV negative but are at high risk of exposure to HIV; includes medications such as truvada or descovy

post-exposure prophylaxis

tx of prophylactic HIV; for emergency situations when a person may have been exposed to HIV; must be initiated ASAP and absolutely within 72 hours of exposure

poliovirus

cause of poliomyelitis; enveloped, ssRNA; transmissible through fecal-oral route; resistant to acid, bile, detergents; can survive stomach acids when ingested

poliomyelitits

acute enteroviral infection of the spinal cord that can cause neuromuscular paralysis; adheres to mucosal cells on oropharynx and intestine, multiplies and sheds in throat and feces, some leak into blood; spreads to CNS if viremia persists

poliomyelitis treatment and prevention

tx is supportive for pain and suffering ; resp failure may require artificial ventilation; physical therapy may be needed; prevention is vaccination by salk or sabin vaccine

hepatitis A

cubical picornavirus relatively resistant to heat and acid; not carried chronically; fecal-oral transmission, multiplies in small int and enters blood and is carried to liver; results in flu-like symptoms, jaundice seldom present

human rhinovirus

HRV; many serotypes associated with common cold; sensitive to acidic environments; unique molecular surface makes development of a vaccine unlikely; aquired from contaminated hands and fomites

reovirus

nonenveloped segmented dsRNA; causes cold-like upper respiratory infection and enteritis

rotavirus

nonenveloped segmented dsRNA; oral-recal transmission; primary cause of mortality and morbidity resulting from diarrhea in infants and children; treatment with rehydration and electrolyte replacement

transmissible spongiform encephalopathies

TSE; caused by prions; transmission through direct or indirect contact with infected brain tissue or CSF; in humans, causes Creutzfeldt-Jakob Disease

Creutzfeldt-Jakob Disease

CJD; alteration in structure of normal PrP protein found in brain; change in shape converts normal PrP to accumulation of abnormal PrP; results in nerve cell death, spongiform damage, severe loss of brain function