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To address the question of how many distinct parasites are injected when a mosquito bites, we have characterized isolates resulting most probably from a single sporozoite inoculum. We describe the direct and immediate cloning on hepatocyte feeder layers of a Thai and an African Plasmodium falciparum primary isolate and the characterization of 67 independent clones by four techniques totaling nine different markers. This led to three main conclusions: (a) both the phenotypic and genotypic markers revealed an unexpectedly large degree of diversity within the clones from a single isolate; (b) the clones are nonetheless genetically related; and (c) a single mosquito inoculum would most likely be sufficient to generate considerable isolate complexity in the absence of repeated exposure. This diversity, which has been greatly underestimated in previous studies, does not bode well for the development of successful malaria control means.

This study examined the effects of low dose systemic corticoid (methylprednisolone, MP), standard dose antihistamine (terfenadine, TF) or the combination on response to out-of-season acute allergen challenge. We feel that a single dose challenge delivered to the nose may represent real disease imperfectly and in this study used two doses given 1 hour apart, hoping to approximate better the circumstances of natural allergen stimulation. The study used clinical endpoints only: measured nasal airway resistance (NAR), sneeze count, and weight of blown nasal secretions. Subjects showed similar NAR, sneezing, and secretion response to both challenges. With placebo treatment, NAR rose after the first allergen provocation and returned to baseline about 30 minutes later. Antihistamine pretreatment appeared to delay but did not prevent this rise; low dose corticoid partially inhibited it, and the combination totally ablated the response. All active treatments suppressed sneezing and secretion better than placebo. Combination corticoid/antihistamine treatment showed no greater effect on sneeze/secretion than did antihistamine alone; this differs from our findings in separate studies comparing analogous drug combinations in naturally-acquired ragweed hayfever.