Tick-borne pathogens pose a considerable disease burden in Europe and North America, where increasing numbers of human cases and the emergence of new tick-borne pathogens has renewed interest in resolving the mechanisms underpinning their geographical distribution and abundance. For Borrelia burgdorferi and tick-borne encephalitis (TBE) virus, transmission of infection from one generation of ticks to another occurs when older nymphal ticks infect younger larval ticks feeding on the same host, either indirectly via systemic infection of the vertebrate host or directly when feeding in close proximity. Here, expressions for the basic reproduction number, R0, and the related tick type-reproduction number, T, are derived that account for the observation that larval and nymphal ticks tend to aggregate on the same minority of hosts, a tick feeding behaviour known as co-aggregation. The pattern of tick blood meals is represented as a directed, acyclic, bipartite contact network, with individual vertebrate hosts having in-degree, kin, and out-degree, kout, that respectively represent cumulative counts of nymphal and larval ticks fed over the lifetime of the host. The in- and out-degree are not independent when co-aggregation occurs such that [Formula: see text] where 〈.〉 indicates expected value. When systemic infection in the vertebrate host is the dominant transmission route R02=T, whereas when direct transmission between ticks co-feeding on the same host is dominant then R0=T and the effect of co-aggregation on R0 is more pronounced. Simulations of B. burgdorferi and TBE virus transmission on theoretical tick-mouse contact networks revealed that aggregation and co-aggregation have a synergistic effect on R0 and T, that co-aggregation always increases R0 and T, and that aggregation only increases R0 and T when larvae and nymphs also co-aggregate. Co-aggregation has the greatest absolute effect on R0 and T when the mean larval burden of hosts is high, and the largest relative effect on R0 for pathogens sustained by co-feeding transmission, e.g. TBE virus in Europe, compared with those predominantly spread by systemic infection, e.g. B. burgdorferi. For both pathogens, though, co-aggregation increases the mean number of ticks infected per infectious tick, T, and so too the likelihood of pathogen persistence.

中文翻译：

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将tick传播的病原体纳入feeding喂养行为。

壁虱传播的病原体在欧洲和北美构成了相当大的疾病负担，那里的人类病例数量不断增加，新的壁虱传播的病原体的出现重新引起了人们对解决其地理分布和丰度机制的兴趣。对于伯氏疏螺旋体和壁虱传播性脑炎（TBE）病毒，当较大的若虫tick感染以相同宿主为食的幼虫时，感染会从一代generation传播到另一s，这可能是通过脊椎动物宿主的全身感染间接引起的，也可能是当靠近喂食。在此，推导了基本繁殖数R0和相关tick类繁殖数T的表达式，这说明了幼虫和若虫tick趋于聚集在同一少数宿主上的观察，tick喂养行为，称为共同聚集。tick血粉的模式表示为有向，无环，两部分接触网络，单个脊椎动物宿主的度数，亲缘度和度数为kout，分别代表一生中饲养的若虫和幼体tick的累积计数主机。当发生共同聚集时，入站和出站的度数不是独立的，以使[。]表示期望值。当脊椎动物宿主的全身感染是主要的传播途径时，R02 = T，而在同一宿主上共同喂食的tick之间的直接传播是主要的，则R0 = T，并且共聚集对R0的影响更为明显。B的模拟。burgdorferi和TBE病毒在理论壁虱-小鼠接触网络上的传播表明，聚集和共聚集对R0和T具有协同作用，共聚集总是增加R0和T，而聚集仅在幼虫和若虫时增加R0和T也共同汇总。当宿主的平均幼虫负担高时，共聚集对R0和T的绝对影响最大，对于通过共同喂养传播的病原体（例如欧洲的TBE病毒）而言，与之相比，共聚集对R0的最大相对影响最大。全身感染，例如B. burgdorferi。但是，对于这两种病原体，共聚集会增加每个传染性tick虫感染的tick的平均数量，因此病原体持续存在的可能性也会增加。并且当幼虫和若虫也同时聚集时，聚集只会增加R0和T。当宿主的平均幼虫负担高时，共聚集对R0和T的绝对影响最大，对于通过共同喂养传播的病原体（例如欧洲的TBE病毒）而言，与之相比，共聚集对R0的最大相对影响最大。全身感染，例如B. burgdorferi。但是，对于这两种病原体，共聚集会增加每个传染性tick虫感染的tick的平均数量，因此病原体持续存在的可能性也会增加。并且当幼虫和若虫也同时聚集时，聚集只会增加R0和T。当宿主的平均幼虫负担高时，共聚集对R0和T的绝对影响最大，对于通过共同喂养传播的病原体（例如欧洲的TBE病毒）而言，与之相比，共聚集对R0的最大相对影响最大。全身感染，例如B. burgdorferi。但是，对于这两种病原体，共聚集会增加每个传染性tick虫感染的tick的平均数量，因此病原体持续存在的可能性也会增加。与欧洲主要通过全身感染传播的TBE病毒（例如B. burgdorferi）相比。但是，对于这两种病原体，共聚集会增加每个传染性tick虫感染的tick的平均数量，因此病原体持续存在的可能性也会增加。与欧洲主要通过全身感染传播的TBE病毒（例如B. burgdorferi）相比。但是，对于这两种病原体，共聚集会增加每个传染性tick虫感染的tick的平均数量，因此病原体持续存在的可能性也会增加。