Changes in H3 influenza A virus receptor specificity during replication in humans.

Influenza A viruses of the H3 subtype caused the 1968 Hong Kong pandemic, the hemagglutinin (HA) gene being introduced into humans following a reassortment event with an avian virus. Receptor specificity and serum inhibitor sensitivity of the HA of influenza A viruses are linked to the host species. Human H3 viruses preferentially recognize N-acetyl sialic acid linked to galactose by alpha2,6 linkages (Neu5Acalpha2,6Gal) and are sensitive to serum inhibitors, whereas avian and equine viruses preferentially recognize Neu5Acalpha2,3Gal linkages and are resistant to serum inhibitors. We have examined the receptor specificity and serum inhibitor sensitivity of H3 human influenza A viruses from the time they were introduced into the human population to gain insight into the mechanism of viral molecular evolution and host tropism. All of the viruses were sensitive to neutralization and hemagglutination inhibition by horse serum. Early H3 viruses were resistant to pig and rabbit serum inhibitors. Viruses isolated after 1977 were uniformly sensitive to inhibition by pig and rabbit sera. The recognition of Neu5Acalpha2,3Gal or Neu5Acalpha2,6Gal linkages was not correlated with the serum sensitivity. These data showed that the receptor specificity of HA, measured as inhibitor sensitivity, has changed during replication in humans since its introduction from an avian virus.

Post-traumatic cutaneous mucormycosis in diabetes mellitus. Short-term antifungal therapy.

Mucormycosis is infrequently encountered in the pediatric population in any of its forms (nasopharyngeal, disseminated, pulmonary, or cutaneous) and generally is associated with the immunocompromised host. We present an adolescent with poorly controlled diabetes mellitus who developed a progressive skin lesion 3 weeks after a motor vehicle accident. Rhizopus species was isolated from the lesion, and the biopsy revealed a fungal vasculopathy. Control of her diabetes, aggressive surgical intervention and a 10-day course of antifungal therapy (amphotericin B) resulted in a favorable outcome. This article illustrates the importance of considering cutaneous fungal infections, especially those in the class zygomycetes, in the diabetic patient with unusual, severe or persistent skin lesions. Early recognition is essential in order to avoid morbidity and mortality from this unusual opportunistic infection.

Alpha 2-macroglobulin is the major neutralizing inhibitor of influenza A virus in pig serum.

Horse, pig, and rabbit sera contain distinct glycoprotein inhibitors of influenza A viruses that inhibit hemagglutinating activity and neutralize viral infectivity. Although alpha 2-macroglobulin has been identified as the inhibitor in horse serum, the inhibitors in pig and rabbit sera have not been identified. As an initial step in elucidating the structural differences among inhibitor molecules, we sought to isolate the inhibitor in pig serum. The purified inhibitor decreased the hemagglutinating activity of influenza A virus, A/Los Angeles/2/87 (H3N2), and represented the majority of the virus-neutralizing activity in pig serum. The inhibitor corresponded in size to alpha 2-macroglobulin and cross-reacted antigenically with human alpha 2-macroglobulin. Characterization of the inhibitor's oligosaccharide moiety using linkage-specific lectins revealed the presence of N-acetylneuraminic acid-alpha 2,6-galactose but not N-acetylneuraminic acid-alpha 2,3-galactose. These data indicate that alpha 2-macroglobulin is the major neutralizing inhibitor of influenza A virus in pig serum.

Distinct glycoprotein inhibitors of influenza A virus in different animal sera.

Normal horse and guinea pig sera contain the glycoprotein inhibitor alpha 2-macroglobulin, which inhibits the infectivity and hemagglutinating activity of influenza A viruses of the H2 and H3 subtypes. In the current study, the presence of inhibitors of influenza A virus in pig and rabbit sera was investigated. Variants of influenza virus type A/Los Angeles/2/87(H3N2) that were resistant to horse, pig, or rabbit serum were isolated. Analysis of the variant viruses with anti-hemagglutinin (HA) monoclonal antibodies revealed that antigenic changes occurred with the development of serum inhibitor resistance. Characterization of the inhibitors in pig and rabbit sera by using periodate and receptor-destroying enzyme demonstrated that carbohydrate is an important constituent of the active portion of both inhibitor molecules and that sialic acid is involved in the interaction of the inhibitors with influenza virus HA. Nucleotide sequence analysis of the HA molecule revealed that the serum-resistant variants each acquired a different set of amino acid alterations. The multiply resistant variants maintained the original amino acid changes and acquired additional changes. Sequence modifications in the HA involved the conserved amino acids within the receptor binding site (RBS) at position 137 and the second-shell RBS residues at positions 155 and 186. Amino acid changes also occurred within antigenic site A (position 145) and directly behind the receptor binding pocket (position 220). Amino acid alterations resulted in the acquisition of a potential glycosylation site at position 128 and the loss of potential glycosylation sites at positions 246 and 248. The localization of the amino acid changes in HA1 to the region of the RBS supports the concept of serum inhibitors as receptor analogs. The unique set of mutations acquired by the serum inhibitor-resistant variants strongly suggests that horse, pig, and rabbit sera each contain distinct glycoprotein inhibitors of influenza A virus.

Cervical adenitis caused by Staphylococcus epidermidis.

Staphylococcus epidermidis, a human commensal, is a common cause of bacteremia in immunocompromised patients with indwelling medical devices. We report a case of isolated cervical adenitis caused by S. epidermidis in an immunocompetent patient and comment on the presumed pathogenesis.

Application of Directigen FLU-A for the detection of influenza A virus in human and nonhuman specimens.

Directigen FLU-A, a new enzyme immunoassay membrane test, rapidly detects influenza A virus antigen in specimens from patients. Nasopharyngeal washes and pharyngeal gargles were used to determine the effectiveness of the assay as applied to different types of routinely collected clinical samples. All specimens had been previously shown to contain influenza A virus by virus isolation in tissue culture. Directigen FLU-A was 90% sensitive (95% confidence interval, 56 to 99.7%) with nasopharyngeal washes but only 39% sensitive (95% confidence interval, 17 to 64%) with pharyngeal gargles (P = 0.018) when used with samples containing similar amounts of infectious virus (50% tissue culture infective dose, 1.0 to 4.5). The intensity of the positive reaction with Directigen FLU-A did not correlate with the amount of virus in the specimens. Directigen FLU-A was found to detect cell-associated antigen more readily than free virus; only 20 infected cells were required to identify cell-associated influenza A virus antigen, whereas the limit of detection for free virus was 1.63 x 10(3) infectious virus particles. These findings suggest that Directigen FLU-A detects the cell-associated antigen present in clinical specimens rather than free virus. In addition, Directigen FLU-A detected avian and swine influenza A viruses in both cloacal swabs (75% sensitivity) and swine lung homogenates (86% sensitivity), indicating its potential usefulness in the surveillance of nonhuman influenza A viruses.

Comparison of different approaches to measuring influenza A virus-specific hemagglutination inhibition antibodies in the presence of serum inhibitors.

The A/Los Angeles/2/87 (H3N2) (A/LA/2/87) virus is sensitive to inhibitors of hemagglutination present in certain human sera. It was found that the effect of these inhibitors could be removed by treating sera with high-concentration receptor-destroying enzyme or trypsin-periodate or by using inhibitor-resistant viruses in the hemagglutination inhibition (HAI) test. Inhibitor-resistant viruses were not effective for detecting rises in antibody titers in the sera of volunteers infected with the A/LA/2/87 wild-type virus, while rises in antibody titer were readily detected in sera treated with trypsin-periodate and tested against A/LA/2/87 wild-type virus in an HAI test. It is therefore suggested that chemical or enzymatic methods be used to inactivate serum inhibitors and that standard virus be used in the HAI test for the currently circulating H3N2 viruses.