How are they diagnosed?

Reliable and sensitive diagnostic tests are essential for all NTD control programmes, including those for worms.

All parasites have developed mechanisms for spreading to new individual hosts, for example by shedding eggs into the host faeces or urine, or releasing pre-larval stages into the blood stream to be ingested by blood-feeding vectors. Parasitological diagnosis of worm infections is commonly performed by identifying this stage of the life by microscopic examination of blood, faecal or urine samples. Antibody tests are also becoming increasingly available. These approaches are generally easy to use, cost-effective and allow for the high-throughput screening of large populations, whilst having sufficient performance for to detect changes in the prevalence and intensity of infection. They are however known to have low sensitivity, especially at low infection intensities, a problem of increasing importance as programmes get closer to elemination goals.

Watch video tutorials developed by Jimma University in Ethiopia and Ghent University in Belgium which provide detailed information on how to perform both traditional and newly developed methods to diagnose and quantify infections in stool, including Kato-Katz thick smear, McMaster egg counting method and Mini-FLOTAC.

  • STH

    Infection with STH can be readily diagnosed by detection of helminth eggs in stool samples using microscopic techniques. The most widely used approach is the Kato-Katz technique, which is also recommended by the World Health Organization. However, a range of methods, including direct microscopy, formol-ether concentration (FEC), McMaster, FLOTAC, and Mini-FLOTAC, are avialable and used in the field. All copro-microscopic methods have variable performance and similar drawbacks, such as low sensitivity for the detection of light-intensity infection. Sensitivity can be increased by examining multiple slides prepared from the same stool sample or, better yet, from multiple stool samples.

    There are currently no sensitive antibody or antigen based tools for diagnosis of STH infection. Assays based on polymerase chain reaction (PCR) have been developed, although unfortunately these do not appear to be any more sensitive than copro-microscopic techniques.

  • Schistosomiasis

    Diagnosis of schistosomiasis is generally performed using stool or urine examinatin for schistosome eggs. The intestinal schistosomes (including S. mansoni and S. japonicum) are diagnosed by observing eggs in a thick smears of stool samples. As for STH, the most common method is Kato-Katz, which is recommended by the World Health Organization for use in field settings; however, direct microscopy, formol-ether concentration (FEC), McMaster, FLOTAC, and Mini-FLOTAC are also available.  S haematobium eggs are released in urine and are detected by microscopy in a urine sample concentrated by sedimentation, centrifugation, or filtration and forced over a paper or nitrocellulose filter. As for STH, sensitivity is low and can be increased by testing muliple stool or urine samples.

    Commercially available antibody and antigen tests are now also available for screening for both intestinal and urogenital schistosomiasis: these include the urine-circulating cathodic antigen (CCA) strip and the soluble egg antigen enzyme-linked immunosorbant assay (SEA-ELISA). However, performance in field settings is variable. The urinary dipstick for detection of hematuria is also recommended as a relatively inexpensive and potentially accurate proxy for detection of urogenital schistosoma infection.

  • LF

    LF has a wide range of clinical manifestations. The standard method for diagnosing active infection, however, is the identification of microfilariae (mf) in a blood smear by microscopic examination. Blood collection should be timed to coincide with the appearance of microfilariae (the pre-larval stage), which only appear at night when the mostquito vectors are biting. Blood slides are then stained and read under the microscope. The method is inexpensive and feasible at individual and community levels, and provides a measure of intensity of infection (mf per ml).

    More recently, serologic techniques have provided a practical alternative to microscopic detection of mf. Circulating antifilarial antiodies can now be detected using immunochromatographic tests (ICT), which only require a finger-prick blood sample. These tests are easy to use and cost-effective, and so are increasingly being used during mapping surveys. However, they are not quantitative (i.e. they cannot provide information on infection intensity) and so are not recommended for monitoring and evaluation of control.