Abstract
BackgroundLymphatic filariasis caused by Wuchereria bancrofti or Brugia spp. is a public health problem in developing countries. To monitor bancroftian filariasis infections, Circulating Filarial Antigen (CFA) test is commonly used, but for brugian infections only microfilariae (Mf) microscopy and indirect IgG4 antibody analyses are available. Improved diagnostics for detecting latent infections are required.MethodsAn optimized real-time PCR targeting the brugian HhaI repeat was validated with plasma from microfilariae negative Mongolian gerbils (jirds) infected with B. malayi. Plasma samples from microfilaremic patients infected with B. malayi or W. bancrofti were used as positive and negative controls, respectively. PCR results of plasma samples from a transmigrant population in a B. malayi endemic area were compared to those of life-long residents in the same endemic area; and to IgG4 serology results from the same population. To discriminate between active infections and larval exposure a threshold was determined by correlation and Receiver-Operating Characteristics (ROC) curve analyses.ResultsThe PCR detected HhaI in pre-patent (56 dpi) B. malayi infected jirds and B. malayi Mf-positive patients from Central Sulawesi, Indonesia. HhaI was also detected in 9/9 elephantiasis patients. In South Sulawesi 87.4% of the transmigrants and life-long residents (94% Mf-negative) were HhaI PCR positive. Based on ROC-curve analysis a threshold for active infections was set to >53 HhaI copies/μl (AUC: 0.854).ConclusionsThe results demonstrate that the HhaI PCR detects brugian infections with greater sensitivity than the IgG4 test, most notably in Mf-negative patients (i.e. pre-patent or latent infections).
Highlights
Introduction of the Circulating Filarial Antigen (CFA) test forW. bancrofti infections showed that 50% of the population in an endemic area had a latent infection
Wuchereria bancrofti accounts for ~90% of Lymphatic filariasis (LF) cases, while Brugia malayi and B. timori infections account for the remainder [2]
We evaluated the usefulness of the B. malayi HhaI PCR as a diagnostic test, especially focusing on pre-patent, latent (Mf-negative) and occult infections, analyzing an Indonesian transmigrant population, previously analyzed for B. malayi infection using both IgG4 based tests [21,22]
Summary
W. bancrofti infections showed that 50% of the population in an endemic area had a latent infection. Compared to an antigen test used for W. bancrofti infection the qPCR is more expensive, but there is currently no other method available for detecting B. malayi infections in Mf-negative persons with latent infections. Lymphatic filariasis caused by Wuchereria bancrofti or Brugia spp. is a public health problem in developing countries. To monitor bancroftian filariasis infections, Circulating Filarial Antigen (CFA) test is commonly used, but for brugian infections only microfilariae (Mf) microscopy and indirect IgG4 antibody analyses are available. Lymphatic filariasis (LF) affects approximately 120 million people in 73 endemic countries [1]. In bancroftian filariasis, circulating filarial antigen (CFA) can be measured in plasma by a rapid card test [9,10] or enzyme-linked immunosorbent assay (ELISA). Visualizing adult worms by ultrasonography (USG) is possible in W. bancrofti infections which is helpful for monitoring adult worm viability, e.g. after macrofilaricidal treatment [6]
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