Data presented demonstrate the relatively high multiplicity of solids-associated virus in field samples, i.e., wastewater, sludge, and soils. Influent, effluent, and chlorinated effluent samples showed 16.1 to 100% of the total virus demonstrated in samples to be solids associated. Three techniques for freeing solidsassociated virus are described and compared. Using sonication of solids and polyethylene glycol concentration, virus was demonstrated in fully digested sludge (60 days at 34 C), sand at the site of a sewer leak, and dried sludge cake and mud 900 m downstream from a sewage disposal site. These data emphasize the inadequacy of virus concentration techniques that do not include the processing of solids. In situ elution failed to free solids-associated virus.
The distribution of solids-associated viruses in wastewater was studied to determine the effect of treatment processes on viruses associated with solids. Solids less than 0.3 pim in diameter were separated from the liquid phase of each sample by using a continuous-flow centrifuge. The percentage of virus associated with solids larger than 0.3 ,um decreased from 28% in the influent to 3.4% in unchlorinated effluent, and this was accompanied by a 92% decrease in the total concentration of virus. These results indicate that the original solids-associated virus as well as virus that is secondarily adsorbed to mixed liquor-suspended solids is lost during clarification. The total concentration of virus was reduced by 82% by chlorination, and the percentage of virus associated with solids increased to 7.7% upon chlorination, indicating some protection due to association with particles larger than 0.3 ,um. When a suspension of fecal particles and a 0.22-,um filtrate of a fecal homogenate were sonicated, a threefold increase in virus titer was observed in each. This demonstrated that viruses may be attached to particles smaller than 0.22 ,um. Thus, small viral aggregates or viruses attached to submicron particles represented the major portion of solids-associated virus in treated sewage. Viruses associated with solids in water may be protected from inactivation by chlorine and by natural inactivating factors (3, 6, 11, 13). Viruses adsorb to various organic and inorganic solids, and this adsorption is highly dependent on such factors as pH, solids concentration, and metal ion composition (2,9, 10). These findings suggest that virions associated with solids in water may be of primary importance since they would resist inactivation and be transported into receiving waters and possibly back to humans.
Wildlife species from 38 of Florida's 67 counties were surveyed over a 10 year period for the presence of antibody to the five major arboviruses circulating in the state. The routine screening of 7891 sera from wild birds and mammals via the hemagglutination-inhibition (H1) test with selected reactors subjected to serum neutralization testing has 1) provided information regarding geographic distribution and seasonality of circulation of these viruses 2) identified enzootic foci of infection and those species of wildlife most commonly infected and 3) documented the potential value of certain wild mammals as indicators of St. Louis Encephalitis and Venezuelan equine encephalomyelitis virus activity prior to the detection of human cases. Limited studies of Tamiami and Tensaw virus on sera from mammals collected for other purposed provided additional baseline information on the activity of these viruses in Florida mammals. Isolations of eastern equine encephalomyelitis virus were made from the heart of a loggerhead shrike (Lanius excubitor), Tensaw virus from the brain of a gray fox (Urocyon cinereoargenteus), and Keystone virus from the heart of a bluejay (Cyanocitta cristata).
Epidemiologic studies were directed in part by Dr. Emily H. Gates, biological studies by Dr. Wil¬ liam L. Jennings, entomological identification by Karen Meadows, serologic work by Florence Y. Lewis, and statistical analyses by Ingrid Baughman. all on the staff of the Encephalitis Research Center. Public Health Service research grant A1-05504-02,03 partly supported the studies in Florida. De¬ partment of the Army contract DA-49-193-MD-2042 and Public Health Service research grant Al-02686 partly supported the studies at the Uni¬ versity of Pittsburgh, which were sponsored by the Commission on Viral Infections, Armed Forces Epidemiological Board.
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