DNA VIruses Medical Assignment Help

ADENOVIRUSES

Adenovirus infection commonly presents as an acute pharyngitis and extension of infection to the larynx and trachea in infants may lead to croup. By school age the majority of children show serological evidence of previous infection. Certain subtypes produce an acute conjunctivitis associated with pharyngitis. In adults, adenovirus causes acute follicular conjunctivitis and rarely pneumonia that is clinically similar to that produced by Mycoplasma . Adenoviruses have also been implicated as a cause of gastroenteritis without respiratory disease and may be responsible for acute mesenteric lymphadenitis in children and young adults. Mesenteric adenitis due to adenoviruses may lead to intussusception in infants.

Human DNA viruses.

Human DNA viruses.

HERPESVIRUSE

Herpes simplex virus infection

Two types of HSV have been identified: HSV-J is the major cause of herpetic stomatitis, herpes labialis (‘cold sore’), keratoconjunctivitis and encephalitis, whereas HSV -2 causes genital herpes and may also be responsible for systemic infection in the immunocompromised host. These divisions, however, are not rigid, for HSV-J can give rise to genital herpes and HSV-2 can cause pharyngitis. The portal of entry of HSV-1 infection is usually via the mouth or occasionally the skin. The primary infection may go unnoticed or may produce a severe inflammatory reaction with vesicle formation leading to painful ulcers (gingivo-stomatitis). The virus then remains latent, most commonly in the trigeminal ganglia, but may be reactivatedby stress, trauma, febrile illnesses and ultraviolet radiation, producing the recurrent form of the disease known as herpes labialis (‘cold sore’). Approximately 70% of the population are infected with HSV-1 and recurrent infections occur in one-third of patients.In genital herpes the primary infection is usually more severe and recurrences are common. The virus remains latent in the sacral ganglia and during recurrence can produce a radiculomyelopathy, with pain in the groin, buttocks and upper thighs. Primary anorectal herpes infection is now common in male homosexuals.
Immunocompromised patients such as those receiving intensive cancer chemotherapy or those with the acquired immunodeficiency syndrome (AIDS) may develop disseminated HSV infection involving many of the viscera. In severe cases death may result from severe hepatitis and encephalitis. Neonates may develop primary HSV infection following vaginal delivery in the presence of active genital HSV infection in the mother. Caesarean section should therefore be considered in the presence of active genital HSV infection. Humoral antibody develops following primary infection, but mononuclear cell responses are probably more important in preventing dissemination of disease. The clinical picture, diagnosis and treatment are described. Varicella zoster virus infection VZV produces two distinct diseases-varicella (chickenpox) and herpes zoster (shingles). The primary infection is chickenpox. It usually occurs in childhood, the virus entering through the mucosa of the upper respiratory tract. Chickenpox almost never occurs twice in the same individual. The virus then remains latent in dorsal root and cranial nerve ganglia. It may recur as localized disease  limited to a dermatome innervated by a single spinal or cranial sensory ganglion (shingles) and/or may affect a motor nerve such as  the facial nerve, causing facial palsy. Shingles is never the direct result of a primary infection. Patients with chickenpox or shingles are infective, the virus being spread from fresh skin lesions by direct contact or airborne transmission and causing chickenpox in susceptible individuals.

CLINICAL FEATURES

Fourteen to twenty-one days after exposure to VZV, a brief prodromal illness of fever, headache and malaise heralds the eruption of chickenpox, characterized by the rapid progression of macules to papules to vesicles topustules in a matter of hours. In young children the prodromal illness may be very mild or absent. The illness tends to be more severe in older children and can be debilitating in adults. The lesions occur on the face, scalp and trunk, and to a much lesser extent on the extremities. It is characteristic to see skin lesions at all stages of development on the same area of skin. Fever subsides as soon as new lesions cease to appear. Eventually the pustules crust and heal without scarring. Important complications of chickenpox include pneumonia, which generally begins 1-6 days after the skin eruption. Pulmonary symptoms are usually more striking than the physical findings, although a chest radiograph usually shows diffuse changes throughout both lung fields. CNS involvement occurs in about 1 per 1000 and most commonly presents as an acute truncal cerebellar ataxia. The immunocompromised are susceptible to disseminated infection with multi-organ involvement. Shingles (see p. 1015) occurs in adults, particularly the elderly, producing an identical skin lesion to chickenpox, although classically it is unilateral and restricted to a sensory nerve (dermatomal) distribution.

DIAGNOSIS

The diseases are usually recognized clinically but can be confirmed by electron microscopy, immunofluorescence or culture of vesicular fluid and by serology.

TREATMENT

Chickenpox requires no treatment in healthy children and infection results in life-long immunity. However, the disease may be fatal in the immunodeficient or the immunosuppressed, when it is reasonable to use passive immunization, with zoster immune immunoglobulin (ZIG). In the immunocompromised host it is also reasonable to give acyclovir 10 mg kg-l three times daily i.v. for 7 days or vidarabine 10 mg kg-I daily i.v. for 7 days.ytomegalovirus (CMV) infection. Infection with CMV is found worldwide and has its most profound effects as an opportunistic infection in the immunocompromised, particularly in recipients of bonemarrow and solid organ transplants and in patients with AIDS-90% of patients with AIDS are infected with CMV and 95% of this population have disseminated CMV at autopsy. A large proportion (50% +) of the adult population has serological evidence of latent infection with the virus, although infection is generally symptomless.

CLINICAL FEATURES

n healthy adults CMV infection is usually asymptomatic but may cause an illness similar to infectious mononucleosis, with fever, occasionally lymphocytosis with atypical lymphocytes, and hepatitis with or without jaundice. Infection may be spread by kissing, sexual intercourse and blood transfusion. Disseminated fatal infection with widespread visceral involvement occurs in the imrnunocom promised including encephalitis, retinitis, pneumonitis and diffuse involvement of the gastrointestinal tract. Intrauterine infection may have serious consequences on the fetus; CNS involvement may cause microcephaly and motor disorders. Jaundice and hepatosplenomegaly are common and thrombocytopenia and haemolytic anaemia also occur.

DIAGNOSIS

Serological tests can identify latent (IgG) or primary (IgM) infection. The virus can also be identified in tissues by the presence M characteristic intranuclear ‘owl’s eye’ inclusions and by direct immunofluorescence. Culture in human embryo fibroblasts is usually slow but diagnosis can be accelerated by immunofluorescent detection of antigen in the cultures.

TREATMENT

In the immunocompetent, infection is usually self-limiting and no specific treatment is required. In the immunosuppressed, ganciclovir (5 mg kg-l daily for 14-21 days) reduces retinitis and  astrointestinal damage and can eliminate CMV from blood, urine and respiratory secretions. It is less effective against pneumonitis andencephalitis. Drug resistance has been reported and bone  marrow toxicity is common.

Posted by: brianna

Share This