Monday, December 1, 2008
Herpesviridae
Types:Herpes Simplex (HSV-1, HSV-2), Varicella-Zoster virus (VZV), Cytomegalovirus (CMV), Epstein-Barr virus (EBV)
The Herpesviruses are a large group containing more than 70 members that infect organisms from fungi to humans.
The Herpesviruses contain a linear DNA genome and are enveloped (bilayered with surface projections derived from the host cell nuclear membrane). Replication occurs in the host cell nucleus.
Herpesviruses cause acute infections but they are also capable of latency. This can lead to recurrent infections, which are important to the mechanism of host to host transmission
Humans are the natural host for HSV, VZV, CMV and EBV.
PATHOGENESIS:
Herpesviruses infect a range of different cell types, causing different disease scenarios. The skin and mucus membranes are common sites of infection for HSV and VZV; CMV and EBV are more internal (EBV infects B lymphocytes).
The viruses produce intranuclear inclusions and multinucleated giant cells
More specifically:
HSV-1 is responsible for a variety of infections. Most commonly, HSV-1 produces the condition known as gingivostomatitis in which oral cavity vesicles or ulcers form. These lesions may recur frequently as "cold sores" (herpes labialis).
HSV-2 is commonly referred to as genital herpes. This virus produces lesions on the genitals, urethra and bladder. Recurrence may be frequent.
VZV produces the disease varicella and zoster. Varicella is commonly known as chickenpox. This relatively mild infection in children can be more serious in adults, occasionally progressing to pneumonia. A highly contagious disease by touching the blisters or respiratory secretions, or through air. Varicella is characterized by a skin rash appearing first on the head and trunk, and later on the extremities. The skin lesions progress from macules to papules to vesicles to pustules to crusts. These lesions are not prone to scar. Zoster is commonly known as shingles and is a manifestation of varicella infection. Typically occurring in older individuals, the lesions are confined to skin areas.
CMV is a virus found in saliva, urine , semen, cervical secretion and breast milk.
EBV is a virus found in the nasopharynx and salivary glands.
HOST DEFENSES:
Primary infection by Herpesviruses induces antibody, which is protective, but recurrent infections still occur.
The cell-mediated immune response is also important (viral antigens on the cell surface allow detection and killing of infected cells).
EPIDEMIOLOGY:
In lower socioeconomic groups, most individuals are infected subclinically by HSV-1, CMV and EBV. In the higher socioeconomic groups, about half are infected. VZV infects both groups equally. HSV-2 is generally transmitted by sexual contact; the others more commonly by saliva.
CMV can be spread transplacentally (0.5-2.5% newborns have CMV in the urine).
DIAGNOSIS:
Clinical: Generally, the lesions are characteristic and clinical diagnosis is accurate.
Laboratory: Smears of lesions show intranuclear inclusions.
CONTROL:
Sanitary: Avoidance of contacts reduces the incidence of disease but virus may be transmitted by asymptomatic individuals.
Immunological: Vaccines are in development but the problems associated with latency and possible cancers remains. A vaccine for VZV is available. Hyperimmune serum can be used for susceptible or high risk individuals.
Blogged @ 10:34 PM