The immune system and infection

English catches an illness from somebody. German needs two prepositions for the same event, and neither is the one a learner reaches for first. The person takes bei: ich habe mich bei meinem Sohn angesteckt. The illness takes mit: sich mit Windpocken anstecken. Von turns up in the passive instead, ich bin von ihm angesteckt worden, and that is a different sentence with the blame placed elsewhere. The verb is separable and reflexive, so in a main clause the pronoun and the prefix drift apart — sie steckt sich an — and meet again in the perfect, sie hat sich angesteckt. Take away the reflexive and the sentence turns round: er hat die ganze Familie angesteckt means he gave it to all of them. The rest of the list follows an infection from the cell to the statistic, from der Makrophage to die Verdopplungszeit.