Reply: Probable imported rather than autochthonous plasmodium vivax cases in Italy

Abstract

To the editor: Dr Nicastri argues that cryptic sporadic cases may not be considered as autochthonous unless other cases have been identified in a specific geographical area. This is a rigid and not scientifically corroborated assumption that, in our opinion, cannot be generalised. In fact, there is no reason to assume that secondary cases should necessarily occur [1,2], since the generation of a chain of transmission depends strictly on the basic reproductive number R0, which is influenced by a series of factors [3] ranging from prevalence of infection among mosquitoes (likely to be very low when autochthonous introduced cases occur, as demonstrated by the lack of detection of plasmodia among mosquitoes in recent outbreaks in Greece) and probability of exposure of humans to mosquito bites. Dr Nicastri's latter two points pertain to only one of the two cases and have been critically discussed in our article. However, it should be mentioned that the patient who visited Santo Domingo did not report febrile episodes after their return and that the likelihood of very late relapse is very low; thus, we think this patient should be considered as a cryptic case. In conclusion, we do not feel Dr Nicastri's criticism is sufficiently supported by the arguments raised.