At present little is known about the mechanisms influencing the course and severity of parvovirus B19 infection. Antibodies to the parvovirus nonstructural protein NS1 were reported in patients with parvovirus-associated arthritis and those with persisting infection but not in those without complications, suggesting a potential involvement of NS1 or anti-NS1 antibodies in pathogenesis. The immune response to NS1 was examined retrospectively in 33 pregnant women with acute parvovirus B19 infection, 14 of whom experienced symptomatic infection and 19 in whom the infection was subclinical. Antibodies to NS1 were found in 15 (45%) of the women, seven with symptomatic and eight with subclinical infection. No association was found between the development of anti-NS1 antibodies and the occurrence of fetal complications. Of the seven cases in which fetal complications were observed, anti-NS1 antibodies were detected in only three. The finding that an immune response to NS1 can also be demonstrated in patients with asymptomatic infection suggests that anti-NS1 antibodies do not appear to represent a marker for an altered or severe course of infection in pregnant women or to contribute significantly to pathogenesis. Since anti-NS1 antibodies first become detectable at least six weeks postinfection, their presence can be used to exclude acute infection in patients with unclear serology or be used to aid differential diagnosis of rashlike illnesses.
Acute Disease Antibodies, Viral