Staining blindly: an update on coloring techniques for fecal smears in parasitology: a scoping review

Abstract

Dye application for parasite highlighting in the Ova and Parasite exam is a common practice in parasitology diagnosis. Methods: A scoping review investigated how staining solutions interact with parasite structures. After screening 1334 papers, 35 met eligibility criteria. Results: Differentiating background from foreground in the fecal smear under light microscopy is the core of the research on this topic. Refractivity, unevenness of staining, size and temperature were explored to enhance staining protocols. Cryptosporidium spp. and Microsporidia were the main studied species. Conclusion: Studies on diagnostic efficacy outperform those that elucidate the physical–chemical interaction between dyes and parasites. An alternative approach involves technicians using computational tools to reduce subjectivity in fecal smear interpretation, deviating from conventional methods.

Plain language summary

What is this article about?

Coloring parasites during fecal exams has been widely used to find parasites in human feces. We searched for articles that could help us to answer the question: ‘How do dyes give color to parasites?’. Then, we filtered the information from a total of 1334 articles to 35.

What were the results?

Cryptosporidium spp. and Microsporidia are microbes that can be seen only through a microscope. Researchers were interested in these two species in the last 40 years. Differentiating parasites from dirt on a glass slide is the main problem researchers are trying to solve. The way the light goes through parasites under a microscope, variation of staining, size and temperature of dyes have been explored to identify what gives better results in coloring protocols.

What do the results of the study mean?

Little is known about the chemical interaction between dyes and parasites. On the other hand, there are many studies on how good coloring methods are and comparing protocols. An alternative to the conventional approaches in staining parasites is the use of computational tools to reduce doubt in the exam interpretation by technicians.

Executive summary

• Although the staining procedures for parasitology have been widely explored, there is scarce knowledge on the interaction between intestinal parasites and permanent or temporary dyes in the O&P exam.

• Size, shape, color uptake pattern, and refractivity are the main features highlighted throughout the articles for identifying parasites with light microscopy.

• The reviewed authors tend to value the technique's detection efficiency rather than the physical-chemical factors involved in the interaction between parasites and dyes.

• The coloring protocols intend to differentiate background from the foreground, where most of the parasites are placed in the fecal smear.

• Opportunistic pathogens such as Microsporidia and Cryptosporidium spp. raised the awareness of the researchers in the past 40 years.

• High-quality papers generally failed to answer the question: “Are the applied staining protocols original?”

• Moderate-quality articles mostly lack information about the proper application of statistical analysis of results.

• Low-quality articles failed to show information about preserving fecal samples and why the authors chose some specific dyes over others.

• Computational tools can be used to reduce subjectivity by identifying sample patterns that are difficult to technicians to evaluate precisely.

Keywords: :

• cysts
• dyes
• microscopy
• oocysts
• stain

Financial disclosure

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Competing interests disclosure

The authors have no competing interests or relevant affiliations with any organization or entity with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Writing disclosure

No writing assistance was utilized in the production of this manuscript.

Acknowledgments

The authors thank the support of Ana Paula de Morais e Oliveira, for the librarian professional services provided. We also thank Bárbara Caroline Benato for the collaboration with the drafted graphs.

Additional information

Funding

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001.