4 Pathogenic Protozoa
4.1 Context
The increase of anthropogenic pressures on ecosystems has led to the increased
frequency of pollution episodes by biological agents. Among these pollutions, the
faecal contamination of aquatic environments affects numerous regions of the world,
with proven risks to human health [47].
Three protozoan parasites are clearly identified as public health priorities: Cryptosporidium spp., Giardia duodenalis and Toxoplasma gondii. Cryptosporidium and
Giardia are responsible for cryptosporidiosis and giardiasis, respectively. They can
cause significant morbidity in immunocompetent patients, and Cryptosporidium can
lead to death in immunocompromised patients [48]. T. gondii is responsible for
toxoplasmosis, and 30% of the entire human population is chronically infected. An
infection during pregnancy may lead to serious malformations of the foetus. In
humans, the main vector of these biological agents is water contaminated by
human or animal faeces, subsequently used for drinking or irrigating crops
[49]. Their parasitic stages of transmission, i.e. oocysts and cysts, are very robust
under environmental conditions, and they are ubiquitous in aquatic habitats. Cryptosporidium spp. and G. duodenalis are the protozoan parasites most often involved
in water-related epidemics (i.e. due to the ingestion of drinking water or the
accidental ingestion of contaminated water during recreational activities).
The assessment of the microbiological water quality is based on the monitoring of
the occurrence of two bacterial indicators of faecal contamination – Escherichia coli
and Enterococcus – according to the World Health Organization and European
regulations (2006/7/EC) [50]. However, they can be quickly removed from the
environment and are more sensitive than protozoa to environmental stresses
(e.g. temperature variations, pollutants) and disinfection treatments [51]. Consequently, the abundance of these bacterial indicators does not reflect, or very little,
the overall sanitary quality [52, 53]. Indeed, previous studies conducted on the Seine
River demonstrated the lack of correlation between Cryptosporidium and Giardia
concentrations and bacterial indicators in wastewater and river water [54, 55]. The
authors suggest that viral and bacterial indicators are not appropriate to predict
parasite loads in surface waters.
To investigate the occurrence of Cryptosporidium and Giardia in filtered water
samples, the AFNOR NF T 90-455 standard (July 2001) proposes a detection
technique based on both immunocapture on beads and immunofluorescence revelation. This detection is therefore highly specific, but it has not been applied yet to the
detection of T. gondii. Other limitations have been identified: this method requires
large volumes of water and high concentrations of parasites; it is expensive, and it
does not allow for the rapid routine detection of parasites. It is therefore urgent to
improve analytical tools for the detection of these biological contaminants for the
purpose of monitoring water masses, thereby improving the assessment and management of health risks.
Contaminants of Emerging Concern in the Seine River Basin: Overview of. . .
367
4.1 Context
The increase of anthropogenic pressures on ecosystems has led to the increased
frequency of pollution episodes by biological agents. Among these pollutions, the
faecal contamination of aquatic environments affects numerous regions of the world,
with proven risks to human health [47].
Three protozoan parasites are clearly identified as public health priorities: Cryptosporidium spp., Giardia duodenalis and Toxoplasma gondii. Cryptosporidium and
Giardia are responsible for cryptosporidiosis and giardiasis, respectively. They can
cause significant morbidity in immunocompetent patients, and Cryptosporidium can
lead to death in immunocompromised patients [48]. T. gondii is responsible for
toxoplasmosis, and 30% of the entire human population is chronically infected. An
infection during pregnancy may lead to serious malformations of the foetus. In
humans, the main vector of these biological agents is water contaminated by
human or animal faeces, subsequently used for drinking or irrigating crops
[49]. Their parasitic stages of transmission, i.e. oocysts and cysts, are very robust
under environmental conditions, and they are ubiquitous in aquatic habitats. Cryptosporidium spp. and G. duodenalis are the protozoan parasites most often involved
in water-related epidemics (i.e. due to the ingestion of drinking water or the
accidental ingestion of contaminated water during recreational activities).
The assessment of the microbiological water quality is based on the monitoring of
the occurrence of two bacterial indicators of faecal contamination – Escherichia coli
and Enterococcus – according to the World Health Organization and European
regulations (2006/7/EC) [50]. However, they can be quickly removed from the
environment and are more sensitive than protozoa to environmental stresses
(e.g. temperature variations, pollutants) and disinfection treatments [51]. Consequently, the abundance of these bacterial indicators does not reflect, or very little,
the overall sanitary quality [52, 53]. Indeed, previous studies conducted on the Seine
River demonstrated the lack of correlation between Cryptosporidium and Giardia
concentrations and bacterial indicators in wastewater and river water [54, 55]. The
authors suggest that viral and bacterial indicators are not appropriate to predict
parasite loads in surface waters.
To investigate the occurrence of Cryptosporidium and Giardia in filtered water
samples, the AFNOR NF T 90-455 standard (July 2001) proposes a detection
technique based on both immunocapture on beads and immunofluorescence revelation. This detection is therefore highly specific, but it has not been applied yet to the
detection of T. gondii. Other limitations have been identified: this method requires
large volumes of water and high concentrations of parasites; it is expensive, and it
does not allow for the rapid routine detection of parasites. It is therefore urgent to
improve analytical tools for the detection of these biological contaminants for the
purpose of monitoring water masses, thereby improving the assessment and management of health risks.
Contaminants of Emerging Concern in the Seine River Basin: Overview of. . .
367