title: Re-assessing the relationship between sporozoite dose and incubation period in Plasmodium vivax malaria: a systematic re-analysis.
abstract: Infections with the malaria parasite Plasmodium vivax are noteworthy for potentially very long incubation periods (6-9 months), which present a major barrier to disease elimination. Increased sporozoite challenge has been reported to be associated with both shorter incubation and pre-patent periods in a range of human challenge studies. However, this evidence base has scant empirical foundation, as these historical analyses were limited by available analytic methods, and provides no quantitative estimates of effect size. Following a comprehensive literature search, we re-analysed all identified studies using survival and/or logistic models plus contingency tables. We have found very weak evidence for dose-dependence at entomologically plausible inocula levels. These results strongly suggest that sporozoite dosage is not an important driver of long-latency. Evidence presented suggests that parasite strain and vector species have quantitatively greater impacts, and the potential existence of a dose threshold for human dose-response to sporozoites. Greater consideration of the complex interplay between these aspects of vectors and parasites are important for human challenge experiments, vaccine trials, and epidemiology towards global malaria elimination.
authors: Infectious Diseases Programme, Saw Swee Hock School of Public Health, National University of Singapore, MD3, 16 Medical Drive, Singapore 117597, Singapore.
authors: Andrew A
authors: AA
authors: Lover
authors: Infectious Diseases Programme, Saw Swee Hock School of Public Health, National University of Singapore, MD3, 16 Medical Drive, Singapore 117597, Singapore.
authors: Richard J
authors: RJ
authors: Coker
mesh_terms: D000818:Animals; D000852:Anopheles / Q000469:parasitology*; D006790:Host-Parasite Interactions; D006801:Humans; D055256:Infectious Disease Incubation Period; D016780:Malaria, Vivax / Q000453:epidemiology / Q000469:parasitology*; D010966:Plasmodium vivax / Q000502:physiology*; D034101:Sporozoites / Q000502:physiology*