348
R. Annon et al.
1 Introduction
Since the first environmental study on Cryptosporidium, human cryptosporidiosis
has been described in various countries and continents and the reported mean
prevalence of cryptosporidiosis ranges between 1 and 3% in Europe and North
America, and from 5% in Asia to approximately 10% in Africa (Current 1994). In
Israel, cryptosporidiosis has been described among Bedouin communities in
southern communities (El-On et al. 1994; Frazer 1994). Contamination of surface
and groundwaters by Cryptosporidium oocysts and Giardia cysts occurs due to
contact with sewage effluent, feces, slurry discharges, or land runoff.
Many surveys, which were conducted mainly in the USA and the UK, showed
widespread prevalence of both parasites in many raw and some treated waters.
The methods which were and are still used for the concentration and detection of
both parasites are inefficient, and the reported numbers are probably an
underestimation. Studies of surface waters conducted in North America have
shown that Cryptosporidium and Giardia are ubiquitous. Data from seven studies
showed presence of Cryptosporidium oocysts in 9.1 to 100% of the samples, with
oocyst concentrations ranging from 0 to 240 per L- 1 (Madore et al. 1987; Ongerth
and Stibbs 1987; Rose 1988; Rose et al. 1988; Roach et al. 1993). Data acquired
between 1979 and 1986 showed that Giardia cysts are common contaminants of
surface water sources in North America, 18% out of 4423 samples were positive
for cysts (Hibler 1988). A survey in 66 surface water treatment plants in the USA
and one Canadian provincial plant showed that Giardia cysts were present in 17%
out of 83 filtered water effluents and Cryptosporidium oocysts were present in
27% of the drinking water samples. Intensive monitoring conducted from 1988 to
1993 in the USA showed that out of 347 surface water samples, 53.9% were
positive for Giardia and 60.2% were positive for Cryptosporidium (LeChevallier
and Norton 1995). A recent survey in 199 groundwater sites showed that 12% of
the 463 samples were positive for Cryptosporidium and/or Giardia (Hancock et
al. 1997). Reported levels for Cryptosporidium were higher than those of Giardia
and, according to the authors' views, this is probably due to more efficient
methods for collecting Cryptosporidium. In the UK, numerous reports indicated
that all types of surface waters surveyed were positive for both Cryptosporidium
and Giardia (Anon 1990, 1992; Smith et al. 1990, 1993; Humphreys et al. 1995.
In Israel, a preliminary survey that was conducted in 1992 in the north of the
country showed that maximal levels of Cryptosporidium cysts, in surface waters,
were 0.5 L- 1 and Giardia cysts 0.09 L- 1 (Armon et al. 1995). Data on reused water
are scarce and the present study supplies information based on irrigation sources
and their impact on soil and crops.
R. Annon et al.
1 Introduction
Since the first environmental study on Cryptosporidium, human cryptosporidiosis
has been described in various countries and continents and the reported mean
prevalence of cryptosporidiosis ranges between 1 and 3% in Europe and North
America, and from 5% in Asia to approximately 10% in Africa (Current 1994). In
Israel, cryptosporidiosis has been described among Bedouin communities in
southern communities (El-On et al. 1994; Frazer 1994). Contamination of surface
and groundwaters by Cryptosporidium oocysts and Giardia cysts occurs due to
contact with sewage effluent, feces, slurry discharges, or land runoff.
Many surveys, which were conducted mainly in the USA and the UK, showed
widespread prevalence of both parasites in many raw and some treated waters.
The methods which were and are still used for the concentration and detection of
both parasites are inefficient, and the reported numbers are probably an
underestimation. Studies of surface waters conducted in North America have
shown that Cryptosporidium and Giardia are ubiquitous. Data from seven studies
showed presence of Cryptosporidium oocysts in 9.1 to 100% of the samples, with
oocyst concentrations ranging from 0 to 240 per L- 1 (Madore et al. 1987; Ongerth
and Stibbs 1987; Rose 1988; Rose et al. 1988; Roach et al. 1993). Data acquired
between 1979 and 1986 showed that Giardia cysts are common contaminants of
surface water sources in North America, 18% out of 4423 samples were positive
for cysts (Hibler 1988). A survey in 66 surface water treatment plants in the USA
and one Canadian provincial plant showed that Giardia cysts were present in 17%
out of 83 filtered water effluents and Cryptosporidium oocysts were present in
27% of the drinking water samples. Intensive monitoring conducted from 1988 to
1993 in the USA showed that out of 347 surface water samples, 53.9% were
positive for Giardia and 60.2% were positive for Cryptosporidium (LeChevallier
and Norton 1995). A recent survey in 199 groundwater sites showed that 12% of
the 463 samples were positive for Cryptosporidium and/or Giardia (Hancock et
al. 1997). Reported levels for Cryptosporidium were higher than those of Giardia
and, according to the authors' views, this is probably due to more efficient
methods for collecting Cryptosporidium. In the UK, numerous reports indicated
that all types of surface waters surveyed were positive for both Cryptosporidium
and Giardia (Anon 1990, 1992; Smith et al. 1990, 1993; Humphreys et al. 1995.
In Israel, a preliminary survey that was conducted in 1992 in the north of the
country showed that maximal levels of Cryptosporidium cysts, in surface waters,
were 0.5 L- 1 and Giardia cysts 0.09 L- 1 (Armon et al. 1995). Data on reused water
are scarce and the present study supplies information based on irrigation sources
and their impact on soil and crops.