No abstract

Encephalomyocarditis viruses adsorb to introduced organic and inorganic solids in water over a wide range of pH and with various concentrations and species of metal cations. Visible flocculation of solids was not a prerequisite for significant virus association. Virus adsorption to natural solids in various types of natural waters was significant but variable. Clay-adsorbed virus retained its infectivity in tissue culture monolayers. These solids-associated viruses also retained infectivity in mice. Various enteric viruses are excreted in human feces and urine during infection and may be found in raw domestic sewage. Excellent reviews such as those prepared by Grabow (13) and Berger et al. (2) provide ample evidence that the use of secondary treatment processes such as trickling filtration, activated sludge, and oxidation ponds can reduce the infectious virus titers by varying degrees. The removal of infectious viruses by these processes is not complete, however, and each process appears to give variable results. Even chlorination of the secondary effluents may not disinfect the waste waters. This effluent discharged into receiving waters often introduces enteric viruses to those waters. Infectious viruses can be carried in the natural resource to points distant from their origin in sewage. Reports indicate that it is not uncommon for fresh and estuarine waters to carry detectable virus several miles (14,

To ascertain the health risks that may be posed by the land application of sewage sludges, a scheme was devised to determine the types and numbers of pathogenic and potentially pathogenic bacteria present in sludges. A processing treatment was adapted to sludge to give a homogenate which yielded the greatest numbers of viable bacteria. Conventional methods were successful in enumerating Klebsiella, Staphylococcus, gram-negative enteric bacteria, and commonly used indicator organisms. Modifications of conventional methods improved the enumeration of Salmonella, Mycobacterium sp., fluorescent Pseudomonas sp., and Clostridium perfringens. However, Shigella methodology yielded only one isolate. Utilizing the proposed scheme, the population densities of these organisms were estimated in three domestic wastewater sludges. In light of these results, the potential impact of land application of sewage sludges is discussed.

Movement of poliovirus I (Chat) through nonsterile core samples of a sandy forest soil was monitored, using several regimens of loading with either dechlorinated final effluent from an operating activated sludge treatment plant or distilled water. Simulated cycles of rainfall and effluent applications, resulting in ionic gradients, were shown to affect virus movement. Such studies indicate that poliovirus applied in effluents may move considerable distances through this soil after rainfall. Survival of poliovirus in the soil at 4 and 20 C has been monitored for 84 days. During this period, the capacity of the virus to migrate is unchanged.

The development of resistance of outbred white mice to two plaque size variants of Sindbis virus was studied as a function of host age. A sudden drop in mortality occurred over a 3-day period. As little as 1 plaque-forming unit (PFU) per mouse was lethal in 1-day-old animals, whereas inocula of 109 PFU per mouse failed to produce high mortality in weanlings. A comparison of viral growth kinetics shows that early replication was similar in newborns and weanlings but that after 6 to 8 hr the production rate and, therefore, the maximal viral titer were suppressed in weanlings. The data demonstrate a lethal viral threshold. Titers in excess of this level lead to mortality, whereas those below it allow survival.