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Thursday, 28 April 2016

NEW DIAGNOSTIC METHODS IN SCHISTOSOMIASIS

Written by Miguel Ansón Manso | Francisco López Alcutén | María Jesús Andrés Otero, Posted in Volumen 2

Male patient, 23 years old and black, from Af-rica who come to the emergency referral from your primary care physician with hematuria subacute / chronic evolution and lumbar pain. In the analytical highlights eosinophilia (11.7%) and the presence in urine sediment Schistosoma eggs Haematobium is confirmed.

Schistosomiasis is used to group all clinical manifestations caused by different species of the genus Schistosoma, which in its adult stage parasites mainly the portal venous system of man. S. haematobium is trematode blood bladder and produces the bladder or urinary schistosomiasis with hematuria; it can also affect the digestive system, the liver or the lungs of the definitive host.
S. haematobium living in the perivesical plexi, eggs accumulate mainly in the urinary tract and are eliminated in the urine. Sometimes eggs produce inflammatory reactions in other parts of the body being especially severe spinal locations (S. mansoni or S. haematobium) and central nervous system (S. japonicum) (Figure 1)1.

Articulo2 Enquistosomiasis500x402Figure 1. Egg Schistosoma Haematobium observed in urinary sediment patient

The laboratory diagnosis is performed through microscopic vision urinary sediment. The entire pellet was examined for eggs of S. haematobium when clinical suspicion exists. Direct microscopic observation is useful in the initial diagnostic assessment but whose main limitation its low sensitivity in the acute phase of illness or in patients with low intensity of parasitism so should be practiced several screening tests. Besides eliminating the parasite eggs it occurs after several weeks after infection and may be delayed for several months. Once administered the treatment, elimination continues for a relatively long time, without this meaning a therapeutic failure2-5. Figure 2 show an egg of S. haematobium seen in urine sediment.

Articulo2 Esquema500x294Figure 2. Schistosoma lifecycle.


Serological diagnosis is performed by ELISA, determining the antibody titers of anti Schistosome, is a highly sensitive technique that allows early diagnosis of the disease. But the titles may persist positive many months after effective treatment, so it does not differentiate a current infection of a bygone infection, plus it can present cross reactions that interfere in the art2-5.

Molecular diagnosis based on the polymerase chain reaction (PCR) can reach a greater sensitivity for acute schistosomiasis than serology and specificity that can reach 100%6. Common sequences can be amplified from specific primers of the 28S ribosomal RNA region of S. haematobium, S. mansoni and S. intercalatum, in urine samples, to make the diagnosis of the 3 species of schistosomiasis imported2,6,7. Recent studies show high diagnostic efficacy in detecting DNA of all species of schistosomes in urine and faeces but appears to be less effective in serum samples3,4.

A group of Spanish researchers are developing for the diagnosis of schistosomiasis in a mouse model using a variant of PCR called Isothermal Amplification (LAMP: Loop-Mediated Isothermal Amplification Method)8. Multiple primers are used in isothermal conditions (60-65 ° C) for amplification of the target sequence so need not thermocycler. Another advantage is that it is done in one step amplification and detection, because produce huge amounts of amplified product in a relatively short time, the product can be detected easily by turbidity or fluorescence display (Figure 3).

This methodology offers new possibilities in the detection of schistosomiasis and other parasitic among many of its applications.

Articulo2 LAMP500x274Figure 3. LAMP Loop mediated isothermal Amplification, está basado en la síntesis de ADN por desplazamien-to de cadena, usa una polimerasa con actividad de desplazamiento y cuatro cebadores, dos internos y dos ex-ternos. Los productos finales son una mezcla de ADN en herradura con diferentes longitudes en su tallo y con estructuras con múltiples bucles

References:

  • Pereira A, Pérez M. Laboratorio de Parasitología. O F F A R M. 2004 (23); 6.
  • Procedimientos en Microbiología Clínica Recomendaciones de la Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica Editores: Emilia Cercenado y Rafael Cantón.
  •  Enk MJ, Oliveira e Silva G, Rodrigues NB. Diagnostic accuracy and applicability of a PCR system for the detection of Schistosoma mansoni DNA in human urine samples from an endemic area. PloSone 7 2012: e38947.
  • Cnops L, Tannich E, Polman K, Clerin K and Van Esbroeck M. Schistosoma real-time PCR as diagnostic tool for international travellers and migrants. Tropical Medicine and International Health doi:10.1111/j.1365-3156.2012.03060.x. 2012 (17); 10: 1208–1216.
  • Pardo J, Pérez-Arellano JL, Galindoa I, Belhassen M, Cordero M, Muroa A. Diagnóstico de helmintiasis importadas. Laboratorio de Inmunología Parasitaria y Molecular. CISET. Facultad de Farmacia. Universidad de Salamanca.
  • Verweij Jaco J., Rune Stensvold C. Molecular Testing for Clinical Diagnosis and Epidemiological Investigations of Intestinal Parasitic Infections. Clinical Microbiology Reviews 2014 (27) 2: 371–418.
  •  J. Utzinger, S. L. Becker, L. van Lieshout, G. J. van Dam and S. Knopp. New diagnostic tools in schistosomiasis. Clinical Microbiology and Infection. 2015 (21), 6.
  • Fernández-Soto P, Gandasegui-Arahuetes J, Sánchez-Hernández A, López-Abán J, Vicente-Santiago B, Muro A. A Loop-Mediated Isothermal Amplification (LAMP) Assay for Early Detection of Schistosoma mansoni in Stool Samples: A Diagnostic Approach in a Murine Model. PLoS Neglected Tropical Diseases. 2014, 4; 8(9):e3126. DOI: 10.1371/journal.pntd.0003126

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