Contribution of respiratory viruses to the worldwide problem of pneumonia in young children

Effect of zinc salts on respiratory syncytial virus replication

Zinc supplementation decreases the morbidity of lower respiratory tract infection in pediatric patients in the developing world. We sought to determine if zinc mediates a specific inhibitory effect against the major cause of pediatric lower respiratory tract disease, respiratory syncytial virus (RSV). We determined the in vitro inhibitory effect of three zinc salts (zinc acetate, lactate, and sulfate) on the replication of RSV at various concentrations of 10 and 1 mM and 100 and 10 microM. The degree of inhibition of RSV replication was examined in the presence of zinc during preincubation, adsorption, or penetration and was compared with that caused by salts of other divalent cations. Complete inhibition of RSV plaque formation was observed at 1 and 10 mM, representing reductions that were >or=10(6)-fold. At the lowest concentration tested, 10 microM, we observed >or=1000-fold reductions in RSV yield when zinc was present during preincubation, adsorption, penetration, or egress of virus. The therapeutic indices, determined as ratios of 50% toxicity concentration to 50% inhibitory concentration, were 100, 150, and 120 for zinc acetate, zinc lactate, and zinc sulfate, respectively. The inhibitory effect of zinc salts on RSV was concentration dependent and was not observed with other salts containing divalent cations such as calcium, magnesium, and manganese. RSV plaque formation was prevented by pretreatment of HEp-2 cell monolayer cultures with zinc or by addition of zinc to methylcellulose overlay media after infection. The results of this study suggest that zinc mediates antiviral activity on RSV by altering the ability of the cell to support RSV replication.

Maternal vaccines

Acute lower respiratory illness (LRI) is the leading cause of disease worldwide as measured by disability-adjusted life years. New strategies are necessary to decrease the disease burden that is largely borne by infants. Respiratory syncytial virus is the most important cause of LRI in infants. Lower respiratory illness can be prevented by endowing infants with high levels of neutralizing antibodies from mothers whose antibodies are boosted during pregnancy with a potent subunit vaccine. Another important cause of infant mortality is group B streptococcus sepsis in the neonatal period; maternal immunization with a group B conjugate vaccine could prevent this devastating infection.

Common (but not always considered) viral infections of the lower respiratory tract

Viral lower respiratory tract infections continue to cause a great deal of morbidity and mortality in the United States and worldwide, despite advances in treatment options, chemoprophylaxis, and vaccine development. The availability of ribavirin has improved the outlook in high-risk patients who develop respiratory syncytial virus bronchiolitis while intensive efforts are continued to develop an efficacious and safe vaccine. Respiratory syncytial virus immunoglobulin may prove to be a useful tool in the armamentarium of the pediatrician to prevent or modify respiratory syncytial virus disease in individual patients. Influenza vaccination and chemoprophylaxis remain mainstays in the prevention of influenza disease in high-risk individuals. The availability of a vaccine for varicella and a wider dissemination of measles vaccine, particularly in developing nations, may well limit the adverse outcomes associated with pneumonias caused by these two viruses. The transplant patient and other immunocompromised patients will continue to challenge clinicians and scientists to provide innovative and effective therapies for viral infections. The exciting advances in clinical and research virology over the last decade offer much hope to practicing pediatricians who struggle with offering prevention strategies and treatment options for their patients. Viral lower respiratory tract infections will never be eliminated as a clinical problem, although the morbidity and mortality associated with them will continue to improve.