Levin M L, Zemtsova G E, Montgomery M, Killmaster L F
Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
Ticks Tick Borne Dis. 2014 Feb;5(1):33-40. doi: 10.1016/j.ttbdis.2013.07.010. Epub 2013 Nov 5.
A number of spotted fever group (SFG) rickettsiae cause serious infections in humans. Several antigenically related rickettsial agents may coexist within the same geographical area, and humans or vertebrate hosts may be sequentially exposed to multiple SFG agents. We assessed whether exposure of a vertebrate reservoir to one SFG Rickettsia will affect the host's immune response to a related pathogen and the efficiency of transmission to uninfected ticks. Two pairs of dogs were each infected with either Rickettsia massiliae or Rickettsia conorii israelensis, and their immune response was monitored twice weekly by IFA. The four immunized dogs and a pair of naïve dogs were each challenged with R. conorii israelensis-infected Rhipicephalus sanguineus nymphs. Uninfected Rh. sanguineus larvae were acquisition-fed on the dogs on days 1, 7, and 14 post-challenge. These ticks were tested for the presence of rickettsial DNA after molting to the nymphal stage. The naive dogs became infected with R. conorii israelensis and were infectious to ticks for at least 3 weeks, whereas reservoir competence of dogs previously infected with either R. massiliae or R. conorii was significantly diminished. This opens an opportunity for decreasing the efficiency of transmission and propagation of pathogenic Rickettsia in natural foci by immunizing the primary hosts with closely related nonpathogenic SFG bacteria. However, neither homologous immunization nor cross-immunization significantly affected the efficiency of R. conorii transmission between cofeeding infected nymphs and uninfected larvae. At high densities of ticks, the efficiency of cofeeding transmission may be sufficient for yearly amplification and persistent circulation of a rickettsial pathogen in the vector population.
许多斑点热群（SFG）立克次氏体可导致人类严重感染。几种抗原相关的立克次氏体病原体可能在同一地理区域共存，人类或脊椎动物宿主可能会依次接触多种SFG病原体。我们评估了脊椎动物宿主接触一种SFG立克次氏体是否会影响宿主对相关病原体的免疫反应以及向未感染蜱虫传播的效率。两对狗分别感染马赛立克次氏体或以色列康氏立克次氏体，每周通过间接免疫荧光法（IFA）监测它们的免疫反应两次。四只免疫的狗和一对未免疫的狗分别用感染了以色列康氏立克次氏体的血红扇头蜱若虫进行攻击。在攻击后第1天、第7天和第14天，用未感染的血红扇头蜱幼虫在这些狗身上进行获取性取食。这些蜱虫蜕皮至若虫阶段后检测立克次氏体DNA的存在情况。未免疫的狗感染了以色列康氏立克次氏体，并且至少3周内对蜱虫具有传染性，而先前感染过马赛立克次氏体或以色列康氏立克次氏体的狗的储存宿主能力显著下降。这为通过用密切相关的非致病性SFG细菌免疫主要宿主来降低致病性立克次氏体在自然疫源地的传播和繁殖效率提供了机会。然而，同源免疫和交叉免疫均未显著影响感染的若虫与未感染的幼虫共同取食时以色列康氏立克次氏体的传播效率。在蜱虫高密度存在的情况下，共同取食传播效率可能足以使立克次氏体病原体在媒介种群中逐年扩增并持续循环。
