Lecture 20: Infection: common diseases
BSCI437
General points: A general listing of different viral diseases that affect different
organs of the body.
• Viruses infect specific
– Organisms
– Tissues
• Effects can range from
– Unnoticeable
– Deadly
Portals of entry
Viruses have to get into the body. Portals of entry are
Conjunctiva (eyes)
Respiratory tract
Alimentary tract
Urogenital tract
Through breaks in skin
Dissemination to organs via the bloodstream
Common Viral Diseases:
 -Respiratory tract-Virus induced respiratory infections kill about 1 million
children each year as well as a significant number of older adults. Many of the
viruses that infect only the respiratory tract do not induce a strong immune
response and hence reinfection with the same or a similar strain is common.
Children get about 6 colds a year and adults 2-3.
 Deaths from respiratory infections: approx. 4.4 x 106/yr for Bact. and viruses
world wide.
 Influenza- 20,000/yr in US during epidemic years (most years), Spanish flu of
1918, 500,000 in US 20 x 106 worlwide, Hong Kong outbreak 68-69, 34,000 in
US.
 HRSV- 4,500/yr (children) in US.
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Rhinitis (Common Cold)-watery nasal discharge and obstruction, sneezing, mild
sore throat and coughing but little or no fever. Infection based in upper
respiratory. Sometimes complicated by superinfection with bacteria which can
lead to progressive hearing loss in some cases.
Pharyngitis (most are viral)-sore throat, malaise, fever, sometimes cough.
Infection based in pharynx. Can be caused by many of the same agents that
cause common colds. RSV and adenovirus are prominent causes in young
children and Herpes type viruses in young adults.
Laryngotracheobronchitis (Croup)-fever, barking or metallic cough, respiratory
distress, sometimes complete laryngeal obstruction. Most common causes are
influenza and parainfluenza virus.
Bronchiolitis-Rapid and labored breathing, persistent cough, wheezing, cyanosis,
variable amount of atelectasis, marked emphysema. Major causes are Influenza,
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parainfluenza, and RSV especially in young children. RSV can develop
virtually overnight causing SIDS in young children.
Pneumonia-often develops following upper resp. tract infection. Febrile, some
cough, degree of dyspnea, wheezing, moist rales. X-rays often show only
scattered areas of consolidation and diffuse lesions unlike pronounced lesions
and consolidated areas in bacterial pneumonia. RSV, Influenza, parainfluenza,
adenoviruses are major causes. A major cause of death to older people and
young children. RSV is the major respiratory pathogen in young children and
kills 4,500 children a year in the U.S. alone.
-Viral Gastroenteritis - Inflammation of the stomach and intestines usually manifested
as diarrhea which is watery but not bloody in the case of viral infection. Fever and
Vomiting are also common with some infectious agents. Diarrheal diseases kill 3 million
children each year mostly in developing countries. Rotaviruses are the main culprits and
are responsible for most of the deaths. Astroviruses and Caliciviruses (Norwalk virus)
can also cause diarrhea.
-Central Nervous system diseases - Most viral infections result as rare complication of
primary infections elsewhere in the body. Viruses may be neuroinvasive (able to enter
the nervous system) and/or neurovirulent (cause nerve damage). Mumps is highly
neuroinvasive but not very neurovirulent while herpes is just the opposite. Viruses cause
disease in a variety of ways including infection of a specific area (Ammon's horn with
rabies, and temporal lobes with HSV) while some infect broadly. Some lyse neurons
while some cause demyelination of axons.
 Deaths - Measles which can cause a variety of brain infections kills about 1
million/yr worldwide, mostly in area without vaccination.
 Meningitis-Infection of meningeal cells. Viruses are major cause but viral
infection is much less severe than bacterial with full recovery likely. Headache,
Fever, and neck stiffness with/or without vomiting and photophobia are
symptoms. Mumps and Enteroviruses are most common agents.
 Paralysis-Mostly from poliovirus in countries where the virus has not been
eradicated. Poliomyelitis involving demyelination of nerve cells.
 Encephalitis-Fever, headache, neck stiffness, vomiting, alterations in state of
consciousness indicating involvement of brain parenchymal tissue. Patient is
lethargic and confused and seizures, or paralysis may develop before coma and
death. Recovering patience may show permanent damage such as retardation,
epilepsy, paralysis, deafness, blindness. Many Arboviruses can cause and
Herpesviruses cause some severe varieties. Mumps is a very common cause but
the disease is generally mild in this case.
 Postinfectious Encephalitis- Occurs a few days after infection of children with
measles, mumps, or varicella. Severe demyelination is observed and prognosis
is grim.
 Guillain-Barre syndrome- Demyelination is common finding. Most frequently
caused by EBV infection and appearing 1-4 weeks after mononucleosis
infection. Most recover completely but 15% have residual nerve damage.
 Reye's syndrome-Cerebral edema without inflammation is common symptom.
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25% of cases are fatal. Follow influenza or chickenpox infection in children
and seems to be an association between syndrome and aspirin administration.
AIDS Dementia Complex-Results from destruction of nerve cells often late in
AIDS syndrome. Direct destruction of nerve cells and demyelination are
involved.
Skin Rashes
 Macular-Flat colored spots;
 Papular-Slightly raised containing no expressible fluid;
 Vesicles-blister with clear fluid from which virus can be isolated;
 Pustular- Blisters containing puss;
 Nodular- Generally warts.
Hemorrhagic fever
 A variety of diseases that share the common feature of widespread hemorrhages
from the bodies epithelial tissue including internal mucosa such as the
gastrointestinal tract and the skin.
 A variety of internal damage is often associated with the different diseases.
 Hanta virus for example causes severe renal necrosis.
 Other agents (Ebola and Yellow fever virus) cause severe liver damage.
 Many have high fatality rates.
Genitourinary infections
Herpes simplex virus 2 and Papillomaviruses are the major viruses infecting the genital
area. Sexual transmission is the main way of acquiring the agent. Herpes manifests as
painful itchy ulcerated vesicular lesions occasionally accompanied by fever and malaise
especially in woman. Spread to the central nervous system occurs in 10% of cases with
mild meningitis resulting. Recurrences are common although generally less severe than
the initial infection. Prior infection with HSV-1 often makes HSV-2 infection less
severe. Papillomaviruses: cause genital warts. Warts appear as external condyloma and
usually disappear without treatment within a couple of years. Certain types of HPV may
progress over several years through stages of cervical intraepithelial neoplasia (CIN) to
invasive squamous cell carcinoma.
Deaths by HIV-about 1 million/yr worldwide, 20,000/yr in US although was
much higher before triple drug therapy
Eye diseases
A number of common childhood viral diseases can involve conjunctivitis (Inflammation
of the conjunctiva which is the transparent membrane covering the sclera (white of the
eye and the inner eyelid). Results in redness, discomfort and discharge and is commonly
called pink eye. Some types are particularly dangerous, especially those involving the
cornea (keratoconjunctivitis). HSV which is associated with this is the commonest
infectious agent that causes blindness in the Western world. A number of eye diseases
including cataracts, glaucoma, and retinopathy are associated with congenital rubella
syndrome and cytomegalic inclusion disease of infants.
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-Viral arthritisStiff and painful joints is usually accompanied by fever and myositis (inflammation of
muscle tissue causing pain tenderness and weakness), with or without rash. It rarely
persists for more than a few weeks. The major causative agents are certain toga, flavi,
and bunyaviruses which are also arboviruses. It has been hypothesized that rheumatoid
arthritis may have a viral origin.
Viral carditis (heart disease).
Myocarditis (inflammation of the heart muscle)
Pericarditis (inflammation of pericardium membrane that encloses he heart)
Cardiomyopathy (diseases causing reduction in the force of the heart)
Associated with certain enteroviruses (a family of picornaviruses), most notably
coxsackie B virus. Infections often reoccur, leading to permanent myocardial damage,
cardiomegaly (enlarged heart), or congestive cardiac failure.
-Viral HepatitisInflammation of the liver with accompanying liver cell damage. There are 20-30 cases
per 100,000 people per year in the U.S.. Symptoms include jaundice (yellowing of the
skin caused by accumulation of bilirubin in the blood), often proceeded by flu-like
illness. Liver failure sometimes occurs. The disease can become chronic depending on
the infectious agent and cirrhosis (characterized by regions of fibrosis (internal scarring)
breaking up the normal structure of the liver). Transmission can be parenteral (needle
infection usually), perinatal (occurring just before or after birth), sexual, or enteric (via
gut cells). Besides the 5 viruses known to infect the liver as the primary organ other
viruses can also cause hepatitis occasionally. Herpes viruses and a number of viruses
causing hemorrhagic fever can also cause hepatitis.
Deaths- Hepatitis B is the most common killer killing 2 million/yr worldwide and
5000/yr in US.
-Viral pancreatitis and diabetesMumps infection can be complicated by severe pancreatitis (inflammation of the
pancreas). Can also be caused by certain other enteroviruses. There is some evidence
that viral infections triggers insulin-dependent juvenile diabetes mellitus.
-Chronic fatigue syndromecharacterized by extreme fatigue. EBV, Coxsackie B, CMV, and HTLV are among the
many viruses to be isolated from such patients, but no cause-effect relationship has been
established.
-Congenital and Perinatal InfectionsThese include a variety of diseases acquired prenatally, intrapartum (during birth process)
or postnatally within the first few weeks. These can be particularly dangerous since the
newborn is not protected by the mothers antibodies.
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