Naming viruses
-No taxa above Family (no kingdom, phylum)
-19 families of animal viruses
-Family name ends in viridae
-Genus name ends in virus

Capsids
All viruses have a protein coat called a capsid that encloses and protects the nucleic acid. A capsid is constructed from identical subunits called capsomers, which are made of protein. There are two types of capsids: Helical and icosohedral.




Host Range
A cell has to have a specific structure or receptor on its surface for a virus to be able to attach to it. A cell has to contain all of the enzymes and materials needed to produce new variations. It can be for one species or for many different ones. Most are specific and infect just humans, dogs, and plants.
The difference between Phage and animal virus replication:
1. Animal virus replication is MORE complex than phage replication because host cells are more complex
2. Animal Viruses cannot inject their DNA
3. Lysogeny for phage, latency for animal viruses

Animal Virus Replication
1. Absorption
2. Penetraion/ uncoating of genome
3. Duplication/synthesis
4. Assembly
5. Release

Ways Cells Are Damaged By Viruses
-changes in size and shape
-cytoplasmic inclusion bodies
-nuclear inclusion bodies
-cells fuse to form multi-nucleated cells
-cell lysis
-alter DNA
-transform cells into cancerous cells

Cell Lysis Multinucleated Cell Cancerous Cell

Viruses
Are obligate parasites that infect animals, plants, and other microbes. Viruses are limited to a particular host or cell type. Most DNA viruses bud off of the nucleus and most RNA viruses multiply and are released from the cytoplasm. Viral infections can range from very mild similar to a cold, to life threatening like HIV. Several viruses are able to cross the placenta and cause developmental disturbances. The term teratogenic is used for the cross infection from mother to the embryo or fetus. A virus can become a permanent resident of the host cell and just stay latent at times. Some cell changes from virus infections are visible to the naked eye ex: inclusion bodies seen from Rabies victims.The first known virus, tobacco mosaic virus, was discovered by Martinus Beijerinck in 1898, and now more than 5,000 types of virus have been described.The study of viruses is known as virology, and is a branch of microbiology.




POXVIRUSES
-produce eruptive skin pustules called pocks or pox that leave scars
-largest and most complex animal viruses
-have the largest genome of all viruses and multiply in the cytoplasm in well defined sites called factory areas which appear as inclusion bodies infected cells.
-multiply in cytoplasm in factory areas
-they are an enveloped DNA virus
-Variola - cause of smallpox
- Vaccinia - (agent of cowpox) closely related virus used in vaccines
- Monkeypox
- Cowpox
-Molluscipox

Smallpox (Variola)



-first disease to be eliminated by a live vaccination (due to Edward Jenner)
-exposure through inhalation (respiratory route) or skin (scabs) contact
-infection associated with fever, malaise, prostration and rash
-Variola major - highly virulent-caused toxemia, shock and intravascular coagulation(20-40% mortality)
-Variola minor - less virulent (1% mortality) milder symptoms and a lower death rate.
-killed majority of some tribes of Native Americans, and people of Hawaii.
-routine vaccination ended in US in 1972
-the last naturally occuring case of smallpox occured in 1977
-vaccine was reintroduced in 2002 because of possible bioterrorism. Mainly inlisted officers/military receive the vaccine when traveling overseas
-Infection includes fever, malaise, prostration. Later a rash begins in the pharynx, spreads to the face, and progresses to the extremities.
-Smallpox caused 300-500 million deaths during the 1900's. As recently as 1967, 2 million people died from smallpox. WHO declared smallpox to be eradicated in 1979.
The CDC and its equivalent in Russia each kept samples of the virus. Threat of bioterrorism has brought the vaccine back.

Q: Which statement regarding the poxviruses is incorrect?
a. They multiply in the cytoplasm.
b. They are non-enveloped DNA viruses.
c. Their sites of multiplication within infected cells appear as inclusion bodies.
A: They are non-enveloped DNA viruses

Q: Which is the causative agent of smallpox?
a. Vaccinia virus
b. Monkeypox virus
c. Variola virus
A: Variola virus

Here is Dr. Larry Brilliant telling the fascinating tale of the eradication of smallpox:





Cowpox



Cowpox virus, from the genus Orthpoxvirus, is another poxvirus that causes human disease through zoonosis.
Epidemiology
Cowpox virus has been found only in Europe and in adjacent parts of the former Soviet Union. Despite its name, the reservoir hosts of cowpox virus are rodents, from which it can occasionally spread to cats, cows, humans, and zoo animals, including large cats and elephants. Transmission to humans has traditionally occurred via contact with the infected teats of milking cows. However, currently, infection is seen more commonly among domestic cats, from which it can be transmitted to humans.
Incubation Incubation period is generally 9 to 10 days.
Symptomatology and Outcome
Infection with cowpox virus in humans produces localized, pustular lesions at the site of their introduction into the skin. The lesion is similar to that caused by vaccination, although the inflammatory response is greater. The lesions in humans usually appear on the hands: on the thumbs, the first interdigital cleft, and the forefinger. Fever and myalgia may be present in some cases, but this is rare. Secondary lesions occur only in individuals with immunological deficiencies.
Pathology and Pathogenesis
The pathology of the skin lesions caused by cowpox virus is similar to that of smallpox. However, there is greater epithelial thickening and less rapid cell necrosis. There is also more involvement of the mesodermal tissues. The most significant pathological feature of cowpox is the presence of two types of cytoplasmic inclusion bodies: irregular B-type inclusion bodies, and numerous large, homogenous, acidophilic, A-type inclusion bodies.
Management and Prevention
Human cowpox usually responds to treatment with antivaccina immunoglobulin. However, this should be restricted to the most severe cases. Usually, the lesions regress spontaneously.
Identification and isolation of animals infected with cowpox can help decrease the incidence of human infections. Attention to the newly emerging prevalence of cowpox virus among domestic cats and subsequent, directive action can also help reduce the number of human infections. Proper hand washing, as with most viruses, is also recommended.


Monkeypox



Human infections with monkeypox virus, from the genus Orthopoxvirus, were first observed in West and Central Africa during the early 1970s, after smallpox had already been eradicated in this region. It also appeared in the Midwestern United States in 2003. Although the signs and symptoms of monkeypox are very similar to those of smallpox, this virus is significantly different.
Epidemiology
The epidemiology of monkeypox is completely different from that of smallpox. This virus is a rare zoonosis found only in the small villages of the tropical rain forests of western and central Africa, with cases mostly reported in Zaire. As a result of intensive surveillance efforts conducted by the World Health Organization, only 400 cases were reported worldwide from the time infection by monkeypox virus was first observed in 1970 to the time when surveillance ceased in 1986.
Monkeypox virus is believed to be transmitted through direct contact with wild animals killed for food, such as squirrels and monkeys. A very important feature of monkeypox is that person-to-person transmission is rare, accounting for less than 1/3 of observed cases.
Incubation period Incubation period is between 10-14 days, usually 12 days.
Pathogenesis and Pathology
Very similar to smallpox where the virus replicates in lymphoid tissues, however, the viral entry occurs by small lesions and it may also occur via respiratory tract.
Prevention and Management
Vaccination with smallpox vaccine immunizes against monkeypox, but it is not justified since the disease is so rare. In the United States, Vaccinia vaccination is recommended for laboratory workers who directly handle cultures or animals infected with monkeypox virus.
Management for monkeypox involves effective surveillance efforts such as those undertaken by the World Health Organization prior to 1980. An important thing to remember is that unlike smallpox, human monkeypox has a lower capacity for human spread. This makes identification and containment much more accessible.

Molluscipoxvirus



Molluscipoxvirus is the most common poxvirus that causes a skin infection called molluscum contagiosum.
Epidemiology
This disease is distributed throughout the world, with highest incidence occuring in the Pacific islands. In endemic regions, it is primarily an infection of children. It is most common in sexually active young people in the United States. Infection results from either sexual or skin-to-skin contact with an infected person. They may be spread to other body sites through scratching and self-inoculation. AIDS patients suffer from an atypical version of the disease, which attacks the skin of the face and forms tumorlike growths, as shown in the image below.

Incubation Period
Incubation period is generally 1-3 months.
Symptoms
The virus causes small, round, firm bumps on the skin. The bumps tend to develop on the sex organs, abdomen, or thighs. The bumps may be pink, pearly-white, or the same color as the rest of the skin in the affected area. There may be one bump or many. They are not painful or tender unless they become infected. Sometimes they itch a little. The infection is confined to the skin and does not cause serious problems.

Treatment
Treatment requires desctruction of the virus by freezing (cryotherapy), electric cautery, and chemical agents applied directly to the lesions.
Molluscum may recur after treatment. If molluscum is not treated, the virus may persist for several months or for as long as a few years and can be transmitted to others during this time.

Herpesvirus

-large enveloped icosahedral capsid housing a core of double-stranded DNA
-replication within nucleus; viral release usually accompanied by cell lysis
-larger family; 8 infect humans (HHV=human Herpes virus)
-latency and recurrent infections, mucous membranes are targets for the virus
-recurrent infection triggered by fever, UV radiation, stress or mechanical injury
-latency complications and recurrent infections more severe with age, chemotherapy, etc.
-most common and serious opportunists among AIDS patients
-most common sporadic form of viral encephalitis in the U.S.
-humans are the only natural reservoir for the virus

Comparative Epidemiology and Pathology of Herpes Simplex, Types 1 and 2

	HSV-1	HSV-2
Usual Etiologic Agent of	Herpes labialis Ocular herpes Gingivostomatitis Pharyngitis	Herpes genitialis
Transmission	Close contact, usually of face	Sexual or intimate contact
Latency	Occurs in trigeminal ganglion	Occurs primarily in sacral ganglia
Skin Lesions	On face, mouth, cold sores, fever blisters (occurs in early childhood)	On internal, external genitalia, thighs, buttocks (occurs in ages 14-29) (can spread without visible lesions)
Complications Whitlows Neonatal encephalitis Treatment	Among healthcare personnel working on oral cavity Causes up to 30% of cases acyclovir, famciclovir, and valacyclovir	Among obstetric, gynecological personnel Causes most cases through contact with birth conal acyclovir, famciclovir, and valacycclovir

Varicella-Zoster Virus (Herpesvirus)
This Herpesvirus causes both varicella (commonly known as chickenpox) and a recurrent infection called herpes zoster (known as shingles).
Varicella
-AKA Chickenpox
-Respiratory tract is chief portal of entry and site of replication.
-communicable through respiratory droplets or active skin lesion fluids
-incubation period is 10-20 days; first symptoms are fever and rash
-most contagious 1 to 2 days prior to the development of the rash
-Skin lesions appear, and progress to scabs, sometimes leaving a scar.
-virus enters neurons and remain latent; may later reactivate in the form of shingles



















Herpes Zoster (Shingles)


As with other herpes viruses, most cases of varicella result in the entry of the varicella into skin sensory nerves, especially thoracic and trigeminal nerves,
where the virus goes dormant. It may either remain dormant indefinately or later reemerge in the form of shingles with its character asymmetrical distribution
on the skin of the trunk or head or occasionally the neck or limbs. Some possible causes may be stress or a weakened immune system. Anyone who has
ever had chickenpox is at risk for the development of shingles, although it occurs most commonly in people over the age of 60.

Pathogenesis and Pathology



Diagnosis, Treatment, and Control
Since shingles has characteristic signs (location and distribution pattern of skin lesions) and symptoms, diagnosis generally does not require any clinical testing.
However, stained smears from vesicle scrapings, flourescent antibody detection of viral antigen in skin lesions, DNA probe analysis, or culture may be done in addition
for confirmation.
Although you can take steps to shorten the duration of a shingles outbreak, the virus must often simply run its course. Postherpetic neuralgia is difficult to manage and can last months or even years, in rare cases. So the best approach is early and immediate treatment. Also, early medical attention may prevent or reduce the scarring that shingles can cause. Medical treatment would be painkillers, antiviral drugs, anti-itch medicated creams, and antibiotics. Tricyclic antidepressants or seizure medication may be prescribed for the pain that may linger after lesions have healed. In 2006, the FDA approved a shingles vaccine called Zostavax. The shingles vaccine is now recommended for everyone age 60 and older. For this age group, the vaccine cuts the occurrence of shingles by about half. Even in those who are vaccinated and still develop shingles, the painful period is reduced. This is a great development because one out of five people who have had chickenpox will eventually get shingles.

Cytomegalovirus Group (CMV) Herpesvirus
-Most often seen virus in humans
-Most prevalent fetal infection
-More common among drug abusers and homosexual population
-Transmitted through saliva, respiratory mucus, milk, urine, semen and cervical secretions

-Usually through sexual contact, vaginal birth, transplacental infection, blood transfusion or organ transplantation

-Newborns infected with CMV often show neurological sequelae, including visual and hearing problems [perinatal CMV, which occurs after exposure to mother's infected birth canal, is usually asymptomatic]
-Newborns tend to develop a more virulent for of cytomegalovirus more than any other age group

Q&A~~Home Page~~Top of Page

Cytomegalovirus Mononucleosis

-Characterized by fever and lymphocytosis, similar to Epstein-Barr Mononucleosis.
-Chiefly adult disease
-Common opportunist of AIDS patients

Epstein-Barr Virus

-Lymphatic disease, can transform lymphocytes to malignant cells through expression of its genes
-Direct oral contact is most common mode of transmission, but transfer through blood transfusions or organ transplantation is possible (can be asymptomatic).
- The niche for Epstein-Barr virus in humans are the lymphoid tissues and salivary glands
-In less-developed areas of the world, EBV occurs more in younger childhood. In industrialized nations, exposure usually doesn't occur until adolescence

-By midlife, 90-95% of population shows serological evidence of infection
-Sore throat, high fever and swollen lymph glands in the neck are the most common symptoms. Blood tests show infected B cells and later infected T cells
-

-Can lead to Burkitt lymphoma, a B-cell malignancy seen most commonly in African children 4-8 years old.

CHRONIC FATIGUE SYNDROME

• Emerged in 1985, when physicians began to see increased number of patients with a so called "new disease"
• Patients reported having clusters of nonspecific symptoms
• disabling fatigue
• memory loss
• sore throat
• tender muscles
• joint pain
• enlarged lymph nodes
• headaches
• most common in Caucasian women between 30 and 50 years of age
• most medical experts now believe that the syndrome has an underlying genetic cause
• treatment with interferon and ampligen have been beneficial in some patients, but so far, ther is no universal remedy

HHV-6

-Causes roseola, an acute febrile disease in babies
-Characteristics are similar to CMV
-Virus enters and replicates in T lymphocytes, macrophages, and salivary gland tissues
-Immunosuppressed patients with renal or bone marrow transplants often acquire HHV-6 infections
-Known for causing encephalitis and neurological disease, which is known to lead to Multiple Sclerosis (MS) [Over 70% of patients with MS show evidence of being infected with HHV-6]
-Link between HHV-6 and several types of cancer (Hodgkin lympoma, oral carcinoma, T-cell leukemias)

Hepadnaviruses

-Hepatitis A-E Viruses
-Enveloped viruses that have never been grown in tissue culture and have a genome containing both double- and single-stranded DNA

-Hepatitis

-Hepatitis is caused when certain viruses infect the liver

-Signs include Jaundice, liver inflammation and liver cell death
-HAV (Hepatitis A Virus)

-Non-enveloped, single-stranded RNA enterovirus transmitted through contaminated food.
-Causes less-severe form of hepatitis that is milder and shorter-term

-(HBV) Hepatitis B Virus

-Hepatitis B multiplies ONLY in the liver, continually supplying blood with infection
-Incidence and risk is highest among:

-Those in crowded living conditions
-Drug abuse (needle-sharing)
-Sexually promiscuous
-Certain medical occupations involving contact with blood or blood serum
-Homosexual males

-Can also be transmitted via mosquitoes, birth canal, and heterosexual intercourse
-Is introduced to body through break in skin or mucous membrane, or direct injection into bloodstream
-A majority of infected persons do not exhibit symptoms, and eventually develop immunity
-Other symptoms include malaise, fever, chills, anorexia, abdominal pain, diarrhea, fever, jaundice, rash, and arthritis
-Can lead to hepatocellular carcinoma
-Vaccination available-a must for medical and dental workers, students, patients receiving multiple transfusions, immunodeficient people and those who have cancer. It is also strongly encouraged for newborns as part of their immunization schedule

-(HCV) Hepatitis C Virus is a flavivirus that causes most cases of transfusion-related hepatitis.

-Causes chronic liver infection, when left undiagnosed leads to severe liver damage and cancer

-(HDV) Hepatitis D Virus

-Defective RNA virus that cannot produce infection unless host also is infected with HBV

-(HEV) Hepatitis E Virus

-Newly identified RNA virus that causes disease similar to HAV, spread by fecal contaminated food and poor hygiene

Adenovirus
-Non-enveloped, dsDNA
-30 types associated with human disease
-infect lymphoid tissue, respiratory and intestinal epithelia and conjuctiva
-oncogenic in animals, not humans
-spread by respiratory and ocular secretions
-causes colds, pharyngitis, conjunctivitis, keroatoconjuctivis, acute hemorrahagic cystitis
-inactivated polyvalent vaccine

Papillomavirus
-papilloma-benign, squamous epithelial growth, wart or verruca
-caused by 40 different strains of HPV
-common seed warts-on fingers, etc.
-plantar wart-soles of feet
-genital warts-prevalent STD
-transmissible through direct contact or contaminated fomites
-Incubation-2 weeks to more than a year

Genital Warts

Vulva and Vagina

-the most common STD in the USA
*Over 6 million new cases each year
*30 million carriers or one of the five types of HPV
associated with genital warts
-Strongly associated with cervical and penile cancer
Type 16 and 18 (vaccine now available)
-podophyllin chemical treatment, cauterization, freezing, laser surgery, immunotherapy

THE PARVOVIRUSES
-Have single stranded DNA molecules
-Extremely small diameter (18-26 nm)
-Can cause disease in several mammalian group
Ex. Distemper in cats, an enteric disease in adult dogs, & potentially fatal cardiac infections in puppies.
Frequently known as the "dog virus- causes stinky bad diarrhea
The most important human parvovirus is B19, the cause of erythema infectiosum. Often the infection goes unnoticed, but child may have a low-grade fever and a bright red rash on the cheeks. This virus can be more dangerous in children with immunodeficiency or sickle-cell anemia, because it destroys red blood stem cells.

The adeno-associated virus (A-AV) is another example of a defective virus that cannot replicate in the host cell without function of a helper cell.

Questions:

Q&A~~Home Page~~Top of Page

1. Who is the father of vaccination?
a. Jeffery Amherst
b. Edward Jenner
c. Dr. Kanatjan Alibekov
d. Louis Pasteur

2. Latent Infections occur when?
a. when it is multiplying and causes symptoms
b. occurs before a lytic infection
c. the viruses enters a dormant phase inside the host cells & becomes inactive.
d. whenever it wants

3. Which of the following diseases have been eliminated?
a. Chickenpox
b. Smallpox
c. Hepatitis C
d. Herpes

4. Who is the man said to be the first to attempt biological warfare?
a. Edward Jenner
b. Louis Pastuer
c. Jeffrey Amherst
d. Ken Alibek

5. What do Herpesviridae and Poxvirus have in common?
a. They are both double stranded in a large envelope
b. They both multiply in the cytoplasm
c. They both cause Monkeypox

6. Which of the following cause Mononucleosis?
a. Herpesviridae
b.Cytomegalovirus
c. Andenovirus
d. Epstein-barr virus

7. In general, zoonotic viral diseases are ____ in humans?
a. mild, asymptomatic
b. self-limited
c. severe, systemic
d. not contagious

8. Which virus is used in Smallpox vaccination?
a. Variola
b. Vaccinia
c. Cowpox
d. Varicella

9. Herpes simplex 1 causes ____, and Herpes simplex 2 causes ____.
a. cold sores, genital herpes
b. fever blisters, cold sores
c. canker sores, fever blisters
d. shingles, stomatitis

10. Herpetic whitlows are ____ infections of the ____.
a. Pox, oral cavity
b. CMV, lymph nodes
c. EBV, skin
d. Herpes, fingers

11. Which virus does not have a double stranded DNA?

a) Adenoviruses
b) Papoviruses
c) Parvovirus
d) Poxviruses
e) Herpesviruses