Mismatched hemagglutinin and neuraminidase specificities in recent human H3N2 influenza viruses.

The hemagglutinin (HA) of influenza viruses initiates infection by binding to sialic acid on the cell surface via alpha2,6 (human) or alpha2,3 (avian) linkage. The influenza neuraminidase (NA) can cleave both alpha2,3- and alpha2,6-linked sialic acids, but all influenza NAs have a marked preference for the non-human alpha2,3 linkage. Recent H3N2 influenza viruses have lost the ability to agglutinate chicken red blood cells. To determine if changes in HA specificity or affinity correlate with NA specificity or activity, we examined red cell binding and elution of a series of H3N2 viruses. We found that the NA activity of many influenza viruses does not release binding by their HA. In some egg-adapted strains, lack of elution correlates with low levels of viral NA activity, and these elute rapidly when bacterial NA is added. However, a Fujian-like virus, A/Oklahoma/323/03, does not elute by its own NA or with Vibrio cholerae sialidase, and it binds to red cells pre-treated with V. cholerae sialidase. It elutes after addition of the broad specificity Micromonospora viridifaciens sialidase. Human glycophorin inhibits A/Oklahoma/323/03 hemagglutination 6-fold better than fetuin. We conclude that specific forms of sialic acid are used as receptor by recent human H3N2 influenza viruses, perhaps involving branched alpha2,6 sialic acid or alpha2,8 sialic acid structures on O-linked carbohydrates. The virus itself has no O-linked glycans, so even though the NA is not able to cleave receptors on cells, the viruses will not self-aggregate. It will be important to monitor efficacy of neuraminidase inhibitors in case there are NA-resistant receptors in the human respiratory tract that allow the viruses to be less dependent on NA activity.

Laboratory-acquired vaccinia infection.

BACKGROUND: Complications following vaccination with vaccinia virus have been well described but are not commonly observed. The use of vaccinia as a tool in molecular biology, in the development of therapeutics, and the anticipated increase of vaccinations in the general population due to the threat of bioterrorism have created a renewed awareness of the post-vaccination complications and the consequent need for clinical and laboratory diagnosis. OBJECTIVES: To report the clinical presentation and subsequent diagnosis of generalized vaccinia that resulted from a laboratory accident in an unvaccinated subject. STUDY DESIGN: The patient was seen by a local infectious disease's specialist and evaluated clinically and with laboratory support relative to a differential diagnosis. RESULTS: Careful assessment of the patient's history, an evaluation of the workplace, and the elimination of likely microbial etiologies led to the diagnosis of generalized vaccinia. Laboratory confirmation was obtained by use of electron microscopy (EM) to observe poxvirus particles in infected cell cultures. CONCLUSIONS: Exposure to vaccinia virus should raise the index of suspicion for patients with skin lesions. Rapid diagnosis may be accomplished by direct examination of lesion material by EM. The virus also readily replicates in commonly available cell cultures and in the absence of immune reagents, typical poxvirus particles may be observed in the infected cells by EM.