| transmission threshold | <epidemiology> Occurs for a parasite when the basic reproductive rate Ro is equal to 1. Below this threshold level the disease is unable to maintain itself within the host population. Typically, for directly transmitted parasites there is a transmission threshold for the host population size. (05 Dec 1998) |
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| transovarial transmission | Passage of parasites or infective agents from the maternal body to eggs within the ovaries; commonly used to describe certain arthropods, to explain the ability of larvae of the next generation to transmit disease pathogens, as with the infection of larval mites or ticks with rickettsiae or viruses. (05 Mar 2000) |
| transstadial transmission | Passage of a microbial parasite, such as a virus or rickettsia, from one developmental stage (stadium) of the host to its subsequent stage or stages, particularly as seen in mites. See: transovarial transmission. (05 Mar 2000) |