Browsing by Author "Hofmann, Natalie"

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    The temporal dynamics and infectiousness of subpatent Plasmodium falciparum infections in relation to parasite density
    (Nature Communications, 2019-03-29) Slater, Hannah; Ross, Amanda; Felger, Ingrid; Hofmann, Natalie; Robison, Leanne; cook, Jackie; Gonçalves, Bronner; Bjòrkman, Andes; Ouedraogo, Andre; Morris, Ulrika; Msellem, Mwinyi; Koepfli, Christian; Muller, Ivo; Tadesse, Fitsum; Gadisa, Endalamaw; Das, Simita; Domingo, Gonzalo; Kapulu, Melissa; Midega, Janet; Owusu-Agyei, Seth; Nabet, Cecile; Piarroux, Renaud; Duombo, Ogobara; Niare, Safiatou; koram, Kwadwo; Lucci, Nami; Udhayakumar, Venkatachalam; Mosha, Jackline; Tiono, Alfred; Chandramohan, Daniel; Gosling, Roly; Mwingira, Felista; Sauerwein, Robert; Paul, Richard; Riley, Eleanor; White, Nicholas; Nosten, Francois; Imwong, Mallika; Bousema, Teun; Drakeley, Chris; Okell, Lucy
    Malaria infections occurring below the limit of detection of standard diagnostics are common in all endemic settings. However, key questions remain surrounding their contribution to sustaining transmission and whether they need to be detected and targeted to achieve malaria elimination. In this study we analyse a range of malaria datasets to quantify the density, detectability, course of infection and infectiousness of subpatent infections. Asymptomatically infected individuals have lower parasite densities on average in low transmission settings compared to individuals in higher transmission settings. In cohort studies, subpatent infections are found to be predictive of future periods of patent infection and in membrane feeding studies, individuals infected with subpatent asexual parasite densities are found to be approximately a third as infectious to mosquitoes as individuals with patent (asexual parasite) infection. These results indicate that subpatent infections contribute to the infectious reservoir, may be long lasting, and require more sensitive diagnostics to detect them in lower transmission settings.
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    Ultra-Sensitive Detection of Plasmodium falciparum by Amplification of Multi-Copy Subtelomeric Targets
    (PLOS, 2015-03-03) Hofmann, Natalie; Mwingira, Felista; Shekalaghe, Seif; Robison, Leanne; Muller, Ivo; Felger, Ingrid
    Background Planning and evaluating malaria control strategies relies on accurate definition of parasite prevalence in the population. A large proportion of asymptomatic parasite infections can only be identified by surveillance with molecular methods, yet these infections also contribute to onward transmission to mosquitoes. The sensitivity of molecular detection by PCR is limited by the abundance of the target sequence in a DNA sample; thus, detection becomes imperfect at low densities. We aimed to increase PCR diagnostic sensitivity by targeting multi-copy genomic sequences for reliable detection of low-density infections, and investigated the impact of these PCR assays on community prevalence data. Methods and Findings Two quantitative PCR (qPCR) assays were developed for ultra-sensitive detection of Plasmodium falciparum, targeting the high-copy telomere-associated repetitive element 2 (TARE-2, *250 copies/genome) and the var gene acidic terminal sequence (varATS, 59 copies/genome). Our assays reached a limit of detection of 0.03 to 0.15 parasites/μl blood and were 10× more sensitive than standard 18S rRNA qPCR. In a population cross-sectional study in Tanzania, 295/498 samples tested positive using ultra-sensitive assays. Light microscopy missed 169 infections (57%). 18S rRNA qPCR failed to identify 48 infections (16%), of which 40% carried gametocytes detected by pfs25 quantitative reverse-transcription PCR. To judge the suitability of the TARE-2 and varATS assays for high-throughput screens, their performance was tested on sample pools. Both ultra-sensitive assays correctly detected all pools containing one low-density P. falciparum–positive sample, which went undetected by 18S rRNA qPCR, among nine negatives. TARE-2 and varATS qPCRs improve estimates of prevalence rates, yet other infections might still remain undetected when absent in the limited blood volume sampled. Conclusions Measured malaria prevalence in communities is largely determined by the sensitivity of the diagnostic tool used. Even when applying standard molecular diagnostics, prevalence in our study population was underestimated by 8% compared to the new assays. Our findings highlight the need for highly sensitive tools such as TARE-2 and varATS qPCR in community surveillance and for monitoring interventions to better describe malaria epidemiology and inform malaria elimination efforts.