cal, and biological vectors, but seldom water sup- 

 plies. No clear distinction exists between fomites 

 and sewage nor should one be made. On-the-farm 

 management of water to avoid dissemination of 

 viruses is compounded by the use of water in 

 the removal of manure prior to the use of dis- 

 infectants or other biological control procedures. 

 It may, therefore, be an oversimplification that 

 viruses generally can be disregarded in water cri- 

 teria. Episodes of diseases and epidemiological 

 studies following them may indicate from time 

 to time that sewage contaminated water supplies 

 are incriminated in outbreaks. In herd manage- 

 ment of livestock virus diseases, direct contact, 

 manure contamination, and water contamination 

 are interlinked and must usually be treated as one 

 problem. 



Viruses are classified by size, ether sensitivity, 

 tissue effects (which include viruses long known 

 to cause recognizable diseases, such as pox and hog 

 cholera), and by other criteria. The first two are 

 important in water criteria, since organization 

 of the infective virus particle and ether sensitivity 

 reflect the susceptibility of the virus particle to 

 degradation in a hostile environment. Small size 

 and ether resistance very likely indicate a greater 

 threat of water transmission over distances; more 

 complex particles with lipid envelopes destroyed 

 by ether may derive benefit from moisture, but 

 are susceptible to degradation by enzymes and 

 electrolytes in the sewage environment. No pur- 

 pose would be served by listing all viruses, but 

 some of those which are ether resistant may call 

 to mind the relationship of these viruses to sewage 

 contamination. These viruses are listed in table 

 IV-13. 



TABLE IV-13. Ether-Resistant Viruses 



Picornaviruses: 

 Polioviruses. 

 Coxsackie viruses — 

 Group A. 

 Group B. 

 Enteric cytopathic human orphan (ECHO) viruses. 

 Rhinoviruses. 



Picornaviruses of lower animals. 



Foot and mouth virus (not present in United States). 

 Teschen's disease of svj'ine (not present in United 



States). 

 African horse sickness (not present in the United 



States). 

 Bluetongue virus of sheep and cattle. 



Parasitic Organisms: Parasites serve as pollu- 

 tants of water supplies when part of their life 

 cycles involve a phase in water. Water supplies 

 in general carry animal forms, which are much 

 reduced in numbers by alum or other precipitation, 



settling, sand filtration, and chlorination. After 

 such treatment, very few parasitic forms can sur- 

 vive the effects of dilution and soil filtration. 

 Natural waters, whether on the surface or under- 

 ground, may play an active role in parasitism, 

 dangerous not only to livestock, but to man as 

 well. 



A careful distinction may be made between the 

 presence of free-living forms and parasites in 

 water. Livestock consume myriads of microor- 

 ganisms found in surface water and even very 

 clear underground water may actually contain 

 many microscopic forms. These organisms may 

 be digested, but sometimes they may be found 

 in lesions where their presence suggests they might 

 be related to the cause. 



Parasitic protozoa include numerous forms 

 which are capable of causing serious livestock 

 losses. Most outbreaks are accomplished by direct 

 spread from animal to animal, but rain water 

 and overflow of piped water supplies may me- 

 chanically spread the infection. Once manure en- 

 ters biologically active environments, such as 

 streams, ponds, or overflow vegetated areas, these 

 organisms rapidly lose their capability of causing 

 disease outbreaks. Very important in human water 

 criteria, these organisms may justifiably be dis- 

 regarded. 



Some of the most important parasitic forms 

 for livestock water criteria are the various flukes 

 which develop as adult forms in man and live- 

 stock. Important ecological factors include pres- 

 ence of snails and vegetation in the water, or 

 vegetation covered by intermittent overflow. This 

 problem is very serious in irrigated areas, but only 

 when snails or other intermediate hosts are avail- 

 able for the complete life cycle. Fluke eggs passed 

 by the host, usually in the manure (some species, 

 in the urine), enter the water and hatch into mira- 

 cidia. These seek out a snail or other invertebrate 

 host where they develop into sporocysts. These 

 transform into redia which in turn may form other 

 redia or several cercariae. The cercariae leave the 

 snail and swim about in the water where they 

 may find the final host, or may encyst on vege- 

 tation to be eaten later. The life cycle is completed 

 by maturing in a suitable host and establishment 

 of an exit for eggs from the site of the attachment. 

 It is not unusual for the fluke to develop in an 

 unsuitable site for egg elimination and unusual 

 tissue reactions sometimes follow location in these 

 aberrant sites. 



Flukes may generally be eliminated in the host 

 by medication or isolation, control of snails, and 

 control of vegetation. An unusual aspect of the 

 problem is water control. In areas of Florida where 



141 



