BIO 220 Ch 24: DNA Viruses

_____ are the smallest parasites and have the simplest biological structure: a DNA or RNA molecule surrounded by a protein coat called a capsid.

Viruses.

A virus is an _____ _____ parasite.

Obligate intracellular.

Why are viruses called obligate intracellular parasites?

They must enter a host cell and direct the cell's genetic and molecular machinery to produce and release new viruses.

What type of nucleic acid does a virus contain?

Either DNA or RNA.

All DNA viruses are _____ except parvoviruses, which have _____ DNA.

Double-stranded; single-stranded.

All RNA viruses are _____ except reoviruses, which have _____ RNA.

Single-stranded; double-stranded.

Viruses are limited to a particular _____ or _____ type.

Host; cell.

Most _____ viruses are involved with replication and transcription in the nucleus and are budded off the nucleus.

DNA.

Most _____ viruses multiply in and are released from the cytoplasm where protein synthesis occurs.

RNA.

How severe can viral infections be?

Can range from asymptomatic to mild to life-threatening.

What are the possible origins of viruses that infect humans?

Many are strictly human in origin, while others are zoonoses transmitted by vectors.

How does a viral infection begin and spread?

A virus invades through a portal of entry and causes a primary infection; it may replicate locally or enter the circulation and infect other tissues.

What are common manifestations of viral infections?

Rashes, fever, muscle aches, respiratory involvement, and swollen lymph nodes.

Which body defenses act together against viral infections?

Interferon, antibodies, and cytotoxic T cells act together against viral infections and frequently produce lifelong immunity.

Some persistent viruses are _____, and some viruses can cross the _____ and cause developmental disturbances and permanent _____.

Oncogenic; placenta; defects.

How may viral diseases be diagnosed?

By symptoms, isolation in cell or animal culture, serological tests for antibodies, and tests for viral antigens.

Animal viruses are classified by their _____ _____ _____, _____, and the presence or absence of an _____.

Nucleic acid core; capsid; envelope.

What structural categories are used for DNA viruses that cause human disease?

Enveloped DNA viruses, nonenveloped double-stranded DNA viruses, or nonenveloped single-stranded DNA viruses.

What characterizes a rapid, virulent viral infection?

It has a rapid course in which the virus undergoes a lytic cycle.

What is a persistent viral infection?

It is a long-term infection that may last for many years or a lifetime.

What is a chronic viral infection?

In a chronic infection, the virus remains detectable in tissue samples and multiplies at a slow rate while symptoms are mild or absent.

What is a latent viral infection?

After a lytic cycle, the virus enters a dormant phase in which it is generally not detectable.

What can happen when a latent virus reactivates?

Reactivation can produce recurrent infections.

In a _____ infection, the virus remains detectable and slowly multiplies; in a _____ infection, the virus is dormant and generally undetectable but can reactivate and cause recurrent infection.

chronic; latent.

What is the etiologic agent of smallpox?

Variola virus.

How is smallpox transmitted?

Through inhalation or skin contact.

What are the main signs and symptoms of smallpox?

Fever, malaise, and a rash of eruptive skin pustules that can leave scars.

variola _____ is highly virulent and can cause toxemia, shock, and intravascular coagulation.

major.

Variola _____ is a less virulent form of smallpox.

minor.

How is smallpox prevented?

By smallpox vaccination.

What is important about current smallpox vaccination?

Routine U.S. vaccination ended in 1972, but vaccination was reintroduced for military and medical personnel in 2002.

What are the etiologic agents of herpes simplex infections?

Herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2).

How is HSV-1 usually transmitted?

By close facial contact or direct exposure to infected secretions.

How is HSV-2 usually transmitted?

By sexual or intimate contact; it can spread even without visible lesions.

What signs and symptoms are usually caused by HSV-1?

Cold sores, fever blisters, and lesions of the mouth or oropharynx.

What signs and symptoms are usually caused by HSV-2?

Lesions on the internal or external genitalia, thighs, or buttocks; oral lesions are also possible.

How are herpes simplex infections treated?

With acyclovir, famciclovir, valacyclovir, or topical medications.

How can herpes simplex transmission be reduced?

Avoid direct contact with infected secretions and active lesions, while recognizing that genital herpes may spread without visible lesions.

What is the etiologic agent of chickenpox and shingles?

Varicella-zoster virus (VZV).

How is varicella-zoster virus transmitted?

By respiratory droplets and direct contact.

What signs and symptoms characterize chickenpox?

Characteristic vesicles form on the skin.

What causes shingles?

Shingles results when latent varicella-zoster virus reactivates.

What signs characterize shingles?

The rash follows affected dermatomes and is more common in older patients.

How are chickenpox and shingles treated?

By treating the symptoms.

How are chickenpox and shingles prevented?

With the live attenuated Varivax vaccine.

What is the etiologic agent of cytomegalovirus infection?

Cytomegalovirus (CMV).

How is CMV transmitted?

Through saliva, respiratory mucus, milk, urine, semen, and cervical secretions.

What is the usual presentation of CMV infection?

Most are asymptomatic, and the virus commonly remains latent in tissues.

Who is most likely to develop severe CMV disease?

Fetuses, newborns, and immunodeficient adults.

What signs and symptoms can congenital CMV cause?

Enlarged liver and spleen, jaundice, capillary bleeding, microcephaly, and ocular inflammation.

What CMV illnesses may occur in immunocompromised patients?

CMV mononucleosis, disseminated CMV, retinitis, pneumonitis, hepatitis, myocarditis, or meningoencephalitis.

How is severe CMV treated in immunocompromised patients?

Course of ganciclovir or valganciclovir.

What is the etiologic agent of Epstein-Barr infectious mononucleosis?

Epstein-Barr virus (EBV).

How is EBV transmitted?

Through direct oral contact and saliva contamination.

What tissues does EBV infect?

Lymphoid tissue and salivary glands.

What are the main signs and symptoms of EBV infectious mononucleosis?

Sore throat, high fever, and cervical lymphadenopathy.

What is the incubation period of EBV infectious mononucleosis?

Approximately 30-50 days.

How is EBV infectious mononucleosis treated?

Treatment is directed at relieving fever and sore throat.

What are the etiologic agents of the three major types of hepatitis?

Hepatitis A virus (HAV), hepatitis B virus (HBV), and hepatitis C virus (HCV).

How is hepatitis A transmitted?

By the oral-fecal route through contaminated food or water.

What are the signs, course, treatment, and prevention of hepatitis A?

It causes fever and gastrointestinal disorder, is usually acute and short, is managed symptomatically, and can be prevented by vaccination.

How is hepatitis B transmitted?

Through blood or serum, sexual or intimate contact, breaks in the skin or mucous membranes, or injection into the bloodstream.

What are the signs, complications, treatment, and prevention of hepatitis B?

It may cause malaise, fever, chills, anorexia, abdominal discomfort, diarrhea, jaundice, rash, and arthritis; chronic disease may cause cirrhosis or liver cancer; treatment includes supportive care or interferon, and prevention includes vaccination, passive immunization, and screening.

How is hepatitis C transmitted?

Through contact with blood or serum and intimate contact.

What are the signs, complications, treatment, and prevention of hepatitis C?

Symptoms resemble hepatitis B, jaundice is common, and chronic infection may cause cirrhosis or cancer; no vaccine is available.

What is the etiologic agent of adenovirus infections?

Adenoviruses.

How are adenoviruses transmitted?

Through respiratory and ocular secretions.

What tissues do adenoviruses infect?

Lymphoid tissue, respiratory and intestinal epithelia, and the conjunctiva.

What respiratory illnesses can adenoviruses cause?

Colds and pharyngitis.

What eye infections can adenoviruses cause?

Conjunctivitis and keratoconjunctivitis.

What other illness can adenoviruses cause?

Acute hemorrhagic cystitis.

How are adenovirus infections treated and prevented?

Severe cases may be treated with interferon, and prevention includes an inactivated polyvalent vaccine.

What are the etiologic agents of common and genital warts?

Human papillomaviruses (HPVs).

How are human papillomaviruses transmitted?

Through direct contact or contaminated fomites.

What is the incubation period for HPV warts?

From 2 weeks to more than 1 year.

What signs are caused by HPV?

Squamous epithelial growths called papillomas, warts, or verrucae, including common, plantar, and genital warts.

What important complication is associated with certain HPV types?

Certain HPV types increase the risk of reproductive cancers.

How are HPV warts treated?

They may regress naturally or be removed with podophyllin, cauterization, freezing, or laser surgery.

How are HPV infection and cervical cancer prevented or detected?

With Cervarix, Gardasil, or Gardasil 9 vaccination and early detection through genital examination and Pap smears.

What is the etiologic agent of fifth disease?

Human parvovirus B19.

What is another name for fifth disease?

Erythema infectiosum, or slapped-cheek syndrome.

Who is commonly affected by fifth disease?

Children.

What are the main signs and symptoms of fifth disease?

Fever and a characteristic rash on the cheeks.

What serious complication can parvovirus B19 cause during pregnancy?

Transmission to the fetus can cause severe, potentially fatal anemia.

What is jaundice?

A yellow tinge of the skin and eyes caused when impaired liver excretion allows bilirubin to accumulate in the blood and tissues.

What is a wart?

A squamous epithelial growth, also called a papilloma or verruca.