Contrasting with infectious diseases in First World countries from either viral and (or) bacterial agents, diseases in the tropics are largely resultant from a totally different group of agents, the protists (single celled animals) and helminths (worms). While there are many viral and bacterial diseases which sometimes overlap between regions and populations of the world e.g. HIV,the disease burden of infectious and parasitic diseases in the tropics is really alarming. More importantly, they continue to be a scourge of socio-economic development, keeping many populations entrenched in grinding poverty through prolonged illness. For protists, the greatest culprit is malaria being present within 140 countries, placing some 3.2 billion people at risk, while for helminths, 650 million people are at risk of schistosomiasis. Collectively both diseases reap greatest havoc in continental Africa where in addition to these, several others are also worthy of mention: protists – trypanosomiasis, leishmaniasis and babesiosis; helminths – lymphatic filariasis, onchocerciasis and soil-transmitted helminthiasis. Rather surprisingly, perhaps, is that nearly all of these diseases are routinely diagnosed by microscopic examinations of either blood, stool or urine specimens. Prior to inspection these samples would have undergone a simple preparative and staining procedure. For example, finger-prick blood is taken and smeared onto a glass slide, dehydrated and then stained with Giemsa which is sufficient to visualise Plasmodium spp. under oil emersion, or stool is size filtered through a specific mesh, smeared and stained with malachite green to visualise Schistosoma and other helminth eggs at 100x magnification. Visualization of eggs, often produced in copious amounts from the adult worm is critical to precise disease identification.
For a fuller description of tropical diseases and their methods of diagnosis reference should be made to Monica Cheesbrough’s excellent text entitled District Laboratory Practice in Tropical Countries (ISBN: 0521676304).
Dr. Russell Stothard is a founding trustee of the Foundation. He is a strong advocate of practical field microscopy and as part of a recent National Control Programme (NCP) in Uganda his team evaluated the Readiview portable microscope. The Abstract is reproduced below:
A SHORT PRIMER ON TROPICAL DISEASE DIAGNOSIS
Dr. J. Russell Stothard
World Health Organisation Collaborating Centre for Schistosomiasis
Honorary Secretary, Royal Society of Tropical Medicine & Hygiene
Reproduced with the kind permission of:
Field evaluation of the Meade Readiview handheld microscope for diagnosis of intestinal schistosomiasis in Ugandan school children
Authors
STOTHARD J. Russell, KABATEREINE Narcis B, TUKAHEBWA Edridah M, KAZIBWE Francis, MATHIESON William, WEBSTER Joanne P, FENWICK Alan
Wolfson Wellcome Biomedical Laboratories, Biomedical Parasitology Division, Department of Zoology, Natural History Museum, London, Schistosomiasis Control Initiative, Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial College, London, Department of Infections and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, Vector Control Division, Ministry of Health, Kampala, UGANDA
Abstract
A novel, inexpensive handheld microscope, the Meade Readiview, was evaluated for field diagnosis of intestinal schistosomiasis by comparison of sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) against conventional compound microscopy as part of a parasitologic survey in nine sentinel schools and a rapid mapping survey across 22 schools in Uganda. Fecal smears from 685 primary school children were examined and the overall prevalence of Schistosoma mansoni was 45%. However, prevalence by school ranged widely from 0% to 100%. For individual diagnosis the Readiview had a sensitivity of 85%, a specificity of 96%, a PPV of 95%, and an NPV of 88%. Due to the poorer movement control of the glass slide on the Readiview stage, fecal smears with less than four eggs could be overlooked. At the highest magnification (160×), egg-like objects could be confounding. Estimating prevalence by school was usually within ± 7% of that of conventional microscopy. Since the Readiview is more robust and portable, both in size and weight, and one-tenth as expensive as the traditional compound microscope, a change in the logistics and costs associated with field infection surveillance is possible. This inexpensive microscope is a pragmatic alternative to the compound microscope. It could play an important role in the collection of prevalence data to better guide anthelmintic drug delivery and also empower the diagnostic capacity of peripheral health centers where compound microscopes are few or absent.
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