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Table 2

Methods to determine (oo)cyst viability and their application in exposure assessment.

Methods Parasites Applications

Detection in naturally contaminated samples Agreement with infectivity assays Determination of the efficacy of control measuresa Agreement with infectivity assays
Excystation
   Ability of trophozoites / sporozoites to escape from the cysts / oocysts after stimulation
Cp Drinking water [80] NA Simple matrixb:
   H2O2-based disinfectants [176]
   Chlorine [29], Chlorine dioxide, Monochloramine [129]
   Ozone [29,34,73,129]
   Ammonia [116]
   Liming, alum and ferric sulfate floccing [183] NA
   UV [77,89,123,154,158]
   Freezing [183] NA
   Storage at 4 °C and 10 °C (8 w) [142]
   Dessication [183] NA
G NA NA Simple matrix:
   Vinegar (acetic acid 4%) à 4 °C et 21 °C [45] NA
   UV [84]
   Storage at 4 °C (up to 56 d) [25] NA
Vital dye-exclusion (propidium iodide)
   Ability of cells to exclude the dye (membrane intact cells) & staining of dead cells
Cp Wastewater [6] NA Simple matrix:
Surface water [190] §    H2O2-based disinfectants [176]
Marine water [191] NA    Chlorine [29]
Drinking water [6] NA    Ozone [29,34]
Cockles, mussels, clams [90] NA    Ammonia [116]
   Liming, alum and ferric sulfate floccing [183]

NA
Oysters [90,191] NA    UV [77,89,154,158] +/−
   Freeze-thaw [121] NA
   Freezing [183] NA
   Storage 4 °C and 20 °C (12 w) [166] NA
   Dessication [183] NA
G Drinking and wastewater [6] NA Simple matrix:
   UV [37,84,162]
   Gamma radiation [203]
   Storage 4 °C (up to 56 d) [24] NA
RT-PCR
   Ability of cells to produce mRNA
Cp NA NA Simple matrix:
   H2O2 [hsp70] [144] NA
   Chlorine, Chlorine dioxide, MOS [hsp70, β-tubulin] [15,97]
   Ozone [hsp70] [97] NA
   Ammonia [hsp70] [144] NA
       Heat 60 °C to 95 °C [hsp70] [97,209]
   Freeze [hsp70] [97] NA
   Storage 15 °C (9 m) [cpag] [114,115] +/−
   Storage 4 °C (48 m) [hsp70] [144] NA
   Storage RT and 4 °C (20 to 39 w) [β-tubulin] [226] +
Food matrix:
   Storage 4 °C (8 d) − Basil [hsp70] [104] NA
G Wastewater [17,24] NA Simple matrix:
   Heat 60 °C to 95 °C [β-giardin] [209]
Food matrix:  
   Storage 4 °C (8 d) − Basil [β-giardin] [104] NA
T NA NA Simple matrix:
   Chlorine-based disinfectant [sporoSAG, ACT1] [218] +
   Acidified ethanol and iodophore-based disinfectant +
[sporoSAG, ACT1] [218]
   Formalin [sporoSAG, ACT1] [218]
     UV [sporoSAG, ACT1] [223]
   Heat 60 °C to 80 °C [sporoSAG, ACT1] [209,218]
    Food matrix:
       Storage 4 °C (8 d) − Basil [sporoSAG] [104] NA
FISH
   Ability of cells to produce rRNA
Cp Water [138]
Oysters [93]
NA
NA
Simple matrix:
   Gamma irradiation [185]
NA
   Storage 15 °C (9 m) [93]
G Water [138] NA NA NA
PMA-PCR
   Ability of cells to exclude PMA (membrane intact cells) & no mplification in dead cells
Cp Water [149] NA Simple matrix:  
     H2O2 [144] NA
   Ammonia [144] NA
     Heat 70 °C [33] NA
   Storage at RT (14 m) [33] NA
   Storage 4 °C (up to 48 m) [hsp70] [144] NA
G Water [149] NA NA NA
a

Relevant for water and food industries;

b

Simple matrix: water or buffer.

NA: No available data. Cp: C. parvum; G: Giardia duodenalis; T:Toxoplasma gondii.

H2O2: hydrogen peroxide; UV: ultraviolet; RT: room temperature; m: months; w: weeks; d: days.

(−): no agreement with infectivity assays means that: i) viability and infectivity assays are not concordant (i.e. viability (+) and infectivity (−), and conversely (rarely)); ii) and/or lower inactivation levels or no inactivation are measured by viability assays compared to infectivity assays.

(+): viability and infectivity assays are concordant.

(+/−): agreement with infectivity varies according to studies

§: 12/15 samples showed no correlation with cell culture assays.

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