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Excess conjugate is removed in another wash cycle, and the beads are resuspended in wash buffer. After a wash cycle, antihuman IgG antibody conjugated to phycoerythrin (PE) is added to the mixture and incubated at 37 degrees C. Briefly, serum samples are mixed and incubated at 37 degrees C with sample diluent and dyed beads coated with VZV antigen. The BioPlex 2200 VZV IgG assay uses multiplex flow immunoassay technology. This results in a positive reaction of bright apple-green fluorescence when viewed with a fluorescence microscope.(Package insert: Bion Varicella Zoster Antigen Substrate Slide. Fluorescein-labeled antihuman-IgM antibody is added to the reaction side and binds to IgM antibodies if present. If no antibodies are present, the complexes will not be formed, and the serum components will be washed away. Antibodies, if present, will bind to the antigen forming stable antigen-antibody complexes. Serum is incubated with VZV antigen that is adhered to a glass microscope slide. The presence or absence of IgM-class antibody to varicella-zoster virus (VZV) is determined by an indirect immunofluorescence assay. Serum specimens collected early during acute phase of infection or soon after vaccination may be negative for IgM- or IgG-class antibodies to this virus, respectively. IgG-class antibodies to VZV may be present in serum specimens from individuals who have received blood products within the past several months but have not been immunized or experienced past infection with this virus. Up to one-third of individuals with primary herpes simplex virus (HSV) infections who have experienced prior VZV infection show a heterotypic antibody response to VZV antigen making a differential diagnosis between VZV and HSV difficult in the absence of clear-cut clinical findings. The performance characteristics with individuals vaccinated with the VZV (OKA strain) have not been established. Testing for IgM-class antibodies to varicella-zoster virus (VZV) should be limited to patients with a clinically compatible disease. Results from cord blood, neonates, or immunocompromised individuals should be interpreted with caution. The presence of IgM-class antibodies to VZV is suggestive of acute or recent infection however results should be correlated with clinical presentation. Serologic screening for IgG-class antibodies to VZV will aid in identifying nonimmune individuals. Additionally, immunosuppressed patients are at risk for developing severe VZV-related complications, which include cutaneous disseminated disease and visceral organ involvement.(2,3) Individuals at risk for severe complications following primary VZV infection include pregnant women, in whom the virus may spread through the placenta to the fetus causing congenital disease in the infant. Shingles is an extremely painful condition typically occurring in older nonimmune adults or those with waning immunity to VZV and in patients with impaired cellular immunity.(2) During reactivation, the virus migrates along neural pathways to the skin, producing a unilateral rash, usually limited to a single dermatome. Chickenpox is characterized by a dermal vesiculopustular rash that develops in successive crops approximately 10 to 21 days following exposure.(1) Although primary infection with VZV results in immunity and protection from subsequent infection, VZV remains latent within sensory dorsal root ganglia and upon reactivation, manifests as herpes zoster or shingles. Chickenpox is a highly contagious, though typically benign, disease, usually contracted during childhood. Varicella-zoster virus (VZV), a herpesvirus, causes 2 distinct exanthematous (rash-associated) diseases: chickenpox (varicella) and shingles (herpes zoster).
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