DNA Viruses PDF

DNA Viruses Asmaa Omar Professor of Clinical Pathology-Faculty of Medicine- Assiut University  Medically Important Viruses DNA Viruses Sometimes referred to as the HHAPPPy viruses: Herpes, Hepadna, Adeno, Papilloma, Parvo, P...

DNA Viruses Asmaa Omar Professor of Clinical Pathology-Faculty of Medicine- Assiut University  Medically Important Viruses DNA Viruses Sometimes referred to as the HHAPPPy viruses: Herpes, Hepadna, Adeno, Papilloma, Parvo, Pox Most DNA viruses are double-stranded, show icosahedral symmetry, and replicate in the nucleus. Two DNA viruses break these rules: 1) Parvoviridae: This virus is so simple that it only has a single strand of DNA 2) Poxviridae: This virus is at the opposite end of the spectrum and is extremely complex. Although it does have double-stranded DNA, the DNA is complex in nature, coding for hundreds of proteins. This virus does not have icosahedral symmetry. The DNA is surrounded by complex structural proteins looking much like a box ( POX IN A BOX). This virus replicates in the cytoplasm Non enveloped DNA viruses include many viruses as show below:  The Adenoviruses Nonenveloped, dsDNA 49 types associated with human disease 5 Transmission: Respiratory (coughing and sneezing)  fecal-oral as also spread through infected stools — for example, during a diaper change. Some adenoviruses are contagious in water.  direct contact (eye) such as touching or shaking hands. Touching an infected object or surface, then touching the mouth, nose, or eyes without washing the hands first.  Site of latency: Replication in oropharynx. Disease: Acute respiratory disease, Pharyngitis, pharyngoconjunctival fever, keratoconjunctivitis, pneumonia, hemorrhagic cystitis, disseminated disease, and gastroenteritis in children. Diagnosis: antigen detection, polymerase chain reaction (PCR), virus isolation, and serology. Prevention: Vaccine (Inactivated polyvalent vaccine ).  Papillomavirus Papovaviruses includes: Papilloma and polyomaviruses. dsDNA, non-enveloped, icosahedral DNA viruses. Transmission:  through direct contact or contaminated fomites; incubation – 2 weeks to more than a year  sexual contact for genital warts.  Site of latency: Epithelial tissue. Disease:  Papilloma: benign tumors of squamous cells or skin and genital warts, benign head and neck tumours, anogenital warts.  Oncogenic: Cervical and penile cancer (especially HPV types 16 and 18  It takes 15 to 20 years for cervical cancer to develop in women with normal immune systems. It can take only 5 to 10 years in women with weakened immune systems, such as those with untreated HIV infection.  Human Papillomavirus  Common seed warts – painless, elevated, rough growth; on fingers, etc.  Plantar warts – deep, painful; on soles of feet  Genital warts -morphology ranges from tiny, flat, inconspicuous bumps to extensive, branching, cauliflower-like masses  Most common warts regress over time; they can be removed by direct chemical application of Prescription cream and physical removal by cauterization(burning), freezing, or laser surgery  Warts can recur Diagnosis: Cytology: by Pap smear Early detection through inspection of genitals, women Pap smear to screen for abnormal cervical cells. PCR Prevention: Two effective HPV vaccines.  Parvoviruses Nonenveloped, ssDNA Small diameter and genome size The parvovirus in humans is different than the one by the same name found in dogs and cats. Humans get a different type: B19. Parvovirus B19 is a common infectious disease that is spread from person to person and most often results in no or very mild symptoms. There are two types of parvoviruses: defective and nondefective, 1- The defective parvoviruses, e.g., adeno-associated virus, require a helper virus for replication and it`s unusual. 2-The nondefective parvoviruses are best illustrated by B19 virus is associated with aplastic crises in sickle cell anemia patients and with erythema infectiosum which is a childhood disease. Transmission: (Close contact and respiratory) Human parvovirus is present in the nasal mucus or saliva. The virus can be spread through airborne droplets when an infected person coughs or sneezes. It may also spread through blood or contaminated blood products. Pregnant women who have been infected with parvovirus can spread the virus to the fetus through the placenta.  Site of latency: The virus sometimes targets the cells that mature into red blood cells. Infection causes a temporary stoppage of the production of these cells.  Human Parvoviruses B19 erythroparvovirus cause of erythema infectiosum (fifth disease) known as “slapped cheek” disease, which is very common in school-aged children, rash of childhood Children may have fever and rash on cheeks Severe fatal anemia can result if pregnant woman transmits virus to fetus Adeno-associated virus (AAV) is a defective virus; it cannot replicate in host cell without adenovirus Diagnosis by: 1- Serology 2- Isolation 3- PCR  Clinical Features of DNA Nonenveloped Viruses Virus Nucleic Mode of Types Cause Certain Vaccine acid Transmissio Different Types Cause Available n Diseases Cancer Adenovirus dsDNA Respiratory Yes Yes, in Yes, but ; fecal– (eye and animals but used only oral GIT) not humans in military Human dsDNA Sexual; Yes Yes, in Yes papillomavi skin Warts and humans rus contact cancer cervix Parvovirus ssDNA Respiratory No (fifth No No B19 ; disease) transplacen tal  Enveloped DNA viruses Viruses that have a lipid membrane. Many enveloped viruses, such as HBV, Herpesviruses and Poxviruses are pathogenic to humans and of clinical importance. The lipid envelope of these viruses is relatively sensitive and thus can be destroyed by alcohols such as ethanol or 2-propanol. Enveloped viruses can be killed by  Hepatitis B Virus infection Hepadnaviridae (Hepadnavirus), Dane particles  Transmission: The virus is most commonly transmitted from mother to child during birth and delivery Contact with blood or other body fluids, including sex with an infected partner. Injection-drug use that involves sharing needles, syringes, or drug-preparation Disease: Hepatitis B Acute infection with resolution (90%), fulminant hepatitis. Most coinfected with delta virus (1%). Chronic hepatitis , persistence of hepatitis B surface antigen (HBsAg) for >6 months (9%) followed by resolution (disappearance of HBsAg), asymptomatic carrier state, chronic persistent (systemic disease without progressive liver disease), or chronic active disease (progressive liver damage). Liver cirrhosis. Oncogenic Liver cancer (Hepatocellular carcinoma). Diagnosis - Serological tests to detect viral antibodies or antigen; ELISA tests for surface antigens. - Polymerase chain reaction (PCR). - AST, ALT and Bilirubin Prevention: HBV vaccine; hepatitis B immune globulin. Passive immunization with HBIG for persons exposed, or possibly exposed, including neonates born to infected mothers Primary prevention is vaccination for high risk individuals and encouraged for all newborns and infants Vaccines derived from surface antigen from cloned yeast – 3 doses with boosters  Poxviridae Poxviruses The largest and most complex viruses. Classification: Subfamilies: Orthopoxvirinae: -(smallpox eradicated)-----Human - Molluscum contagiosum----- human -(monkeypox), causes monkeypox in humans and animals----animal - Vaccinia virus used in the smallpox vaccine.  Smallpox : Respiratory transmission Incubation period 10-14 days, After day 7 or so, humans begin shedding virus asymptomatically ORF, COWPOX, AND MONKEYPOX Human infection with the orf (poxvirus of sheep and goat) or cowpox (vaccinia) virus is usually an occupational hazard resulting from direct contact with the lesions on the animal. Monkeypox causes a milder version of smallpox disease. Transmission: Respiratory droplets (smallpox); direct contact (molluscum contagiosum, Orf, monkeypox).  Site of latency: Skin Disease: All are diseases of the skin; smallpox (Variola), is a generalized infection with pustular rash (10%-25% fatal) molluscum contagiosum manifests as benign nodules Orf manifests as localized papules/vesicles monkeypox manifests as a generalized infection that Diagnosis: Smallpox: made either by growing the virus in cell culture or chick embryos or by detecting viral antigens in vesicular fluid by immunofluorescence. Electron microscopy (EM) of material from a skin lesion; polymerase chain reaction (PCR). Molluscum contagiosum: Confirmed histologically by the finding of characteristic large, eosinophilic cytoplasmic inclusions (molluscum bodies) in epithelial cells. These bodies can be seen in biopsy specimens  Prevention: Vaccine for smallpox; avoid contact