Disclosed is a method for determining biological status of at least one eukaryotic organism in a nonhuman sample via determining the presence or absence of at least one target substance, including the steps of: (a) collecting a biological sample (b) preparing the sample (c) forming a mixture of the sample of step (b) with a staining solution that includes at least one dye compound or compounds comprising at least one tetrazolium or diazonium salt that reacts with the target substance(s) in a manner which results in a visible colour change (d) incubating the mixture of step (c) and (e) visibly evaluating the colour of the incubated product of step (d) in the container with the naked human eye and, if the colour (i) remains the same as the staining solution then no viable organism was present in the sample (ii) changes to a darker solution or lighter solution depending on the staining solution chosen, the organism sample contained viable organism.
