Chapter 2: Perform parasitological tests

Applied Biology professionals in Kenya are routinely called upon to perform parasitological tests that inform disease diagnosis, management, and public health interventions. Accurate collection and processing of biological samples is foundational for reliable laboratory results, whether in county hospitals, research institutes, or environmental monitoring sites. This chapter equips students with the practical knowledge and procedural detail necessary to examine faecal, blood, urine, sputum, and skin samples for parasites and their vectors. Mastery of these techniques ensures effective surveillance and control of parasitic diseases across Kenya’s diverse health and ecological settings.

2.1 Collection and processing of samples

A parasitological test is only as reliable as the sample that reaches the bench. How each sample is collected is taught under Sample collection and handling, and how it is packaged, transported and stored under Sample packaging, transportation, processing and storage. This topic joins those steps to the tests that follow: which sample feeds which test, when it must be taken and examined, which preservative suits the planned examination, and how much processing each test needs before it can be read.

Example: a stool sample sent to find hookworm eggs and a stool sample sent to find Giardia trophozoites may arrive in the same kind of container, yet they must be handled differently from the first minutes. Trophozoites die and lose their shape soon after the stool is passed, whereas hookworm eggs keep their shape in formalin until the test is done.

Matching the sample to the test

Each examination in Diagnostic techniques is built for one sample type and for the parasite stages that sample can carry. Choosing the wrong sample, or taking the right one at the wrong time, gives a negative result that means nothing.

Timing that affects the result

Parasites are not released evenly, and they do not survive evenly once the sample is taken. Timing therefore decides whether a parasite that is present is also found.

• Intermittent shedding: many intestinal parasites release eggs and cysts irregularly, so one negative stool does not rule out infection. Three specimens collected on different days improve the chance of finding protozoa.
• Short life of trophozoites: the feeding stage of intestinal protozoa is fragile. In loose stool it must be examined within about 30 minutes, or the stool must go straight into a fixative.
• Periodic release in blood: microfilariae of Wuchereria bancrofti circulate in the blood mainly at night, so blood for them is taken late in the evening or around midnight (about 22:00 to 02:00). Microfilariae of some other species, such as Loa loa, circulate by day. Malaria parasites can be found at any hour, but smears made before treatment give the clearest picture.
• Midday egg output: Schistosoma haematobium eggs are passed mainly around midday, so a morning urine can miss a light infection.
• Effect of treatment: a sample taken after an anti-parasitic or antimalarial drug may contain fewer, damaged or no parasites. The time of any treatment is noted on the request form.
• Ageing of the sample: every hour of delay changes the shape, stain uptake and motility of parasite stages, so the interval between collection and examination is written on the request.

Preservatives and fixatives

When a sample cannot be examined fresh, a preservative keeps the parasite stages recognisable. The choice depends on the examination planned, because a preservative that suits one test can ruin another.

Stool is mixed with formalin or SAF at about 1 part stool to 3 parts fixative, because too little fixative leaves the centre of the lump unpreserved.

Deciding how much processing a test needs

Processing is the step between the sample as received and the preparation that is read under the microscope. Each decision below changes what can be found.

• Direct mount or concentration: a heavy infection often shows in a direct mount. A light infection needs concentration, which gathers the few eggs or cysts from a larger portion of sample.
• Fresh or fixed: motile trophozoites and live microfilariae are seen only in unfixed preparations, whereas permanent stains need a fixative.
• Counting or finding: when the number of eggs must be reported, a measured portion is examined, as in the Kato-Katz method in Faecal examination. Concentration methods raise the chance of finding eggs but lose the link between the count and the amount of stool.
• Antigen and DNA tests: these are done on unfixed or ethanol-preserved material, so a portion is set aside before formalin is added.
• Limited volume: when there is not enough sample for every test, the test most likely to answer the request is done first, and the request form is checked for the suspected parasite.

Example: a 10 g formed stool sample is divided so that every planned test has its own portion.

Checks before a sample is accepted

A sample is checked at the bench before any processing. A sample that fails a check is not processed silently: the reason is told to the sender and a repeat sample is requested.

• Label and request agree: at least two identifiers on the container match the request form. A label that cannot be read or does not match is a reason to refuse.
• Right sample for the test: the sample type matches the examination requested, for example 10 mL of urine for a filtration count.
• Enough material: the volume or mass is enough for every test requested, with some left for a repeat.
• Within the time limit: the time between collection and receipt is acceptable for the test, and any preservative needed has been added in the right proportion.
• No wrong material: urine, water or toilet paper in a stool sample, or saliva in place of sputum, make the sample unsuitable.

How the outcome of these checks is written down is covered in Recording of results.

Safety during processing

Every sample is treated as infectious, because the person or animal it came from may carry organisms other than the one being sought.

• Protective clothing: a laboratory coat, gloves and eye protection are worn for all processing, and gloves are changed when torn or soiled.
• Aerosols: steps that can make aerosols, such as shaking, vortexing and centrifuging, are done in a biological safety cabinet or with sealed centrifuge buckets, above all for sputum.
• Chemicals: formalin and ethyl acetate are used in a well-ventilated space or a fume cupboard, away from flames, and mercury-containing fixatives are collected as hazardous waste.
• Sharps and glass: blades, needles and broken slides go into a puncture-proof sharps container and are never pushed back into a sleeve by hand.

Chapter Summary

This chapter explores the essential procedures for performing parasitological tests, beginning with the proper collection and processing of biological samples to ensure accuracy and reliability. It examines a range of diagnostic techniques, including faecal examination, blood smears, urine analysis, sputum examination, and the assessment of skin scrapings or swabs, each tailored to detect specific parasites and their life stages. The methods for each test are outlined to highlight their practical application in laboratory settings. Emphasis is placed on the importance of precision in sample handling and the use of standardized protocols to minimize errors. The chapter also addresses the systematic recording of results, which is critical for effective diagnosis and treatment planning. By mastering these techniques, professionals can contribute to improved disease surveillance and management. Overall, the chapter provides a comprehensive foundation for conducting parasitological investigations and ensuring the integrity of laboratory findings.