Parasites with Acid Fastness

Microscopy continues to be the mainstay of parasitological diagnosis and offers epidemiological evaluation of parasite burden, particularly in rural and low-resource settings.

Acid fastness is a physical property that gives a pathogen the ability to resist decolorization by acids during staining procedures. This means that once the pathogen is stained, it cannot be decolorized using acids routinely used in the process. This significant and distinctive characteristic of a particular pathogen makes it possible to classify and identify them using relatively simple laboratory techniques like microscopy.

Ziehl-Neelsen (Acid Fast Stain) stain is routinely used for identification of Mycobacterium spp. However, one of the most frequently used stains in parasitology is Modified Acid Fast Stain. This technique is useful for the identification of oocysts of the coccidian species and even few other parasites which may be difficult to detect with routine stains such as trichrome. The Modified Acid-Fast Stain differs most from the Ziehl-Neelsen procedure in that staining does not need heating of the reagents.

Even though acid fastness can be attributed to many different pathogens, correlation with history makes it a fairly unique presentation in clinical practice. As long as clinical correlation is taken into account, this makes acid-fast staining sensitive and specific. The importance of this staining approach in parasitology cannot be neglected, particularly for low and middle-income nations, despite the adoption of extremely sophisticated molecular diagnostic tools.

References:

1. Momčilović S, Cantacessi C, Arsić-Arsenijević V, Otranto D, Tasić-Otašević S. Rapid diagnosis of parasitic diseases: current scenario and future needs. Clin Microbiol Infect. 2019;25(3):290-309.

2. Bayot ML, Mirza TM, Sharma S. Acid Fast Bacteria. In: StatPearls. Treasure Island (FL): StatPearls Publishing; August 8, 2022.

3. Vieira S, Belo S, Hänscheid T. Ziehl–Neelsen in Schistosomiasis: Much More Than Staining the Shell and Species Identification. The American Society of Tropical Medicine and Hygiene. 2016;94(4):699-700.