Line 63: |
Line 63: |
| | | |
| '''Epidemiology''' | | '''Epidemiology''' |
| + | *Determined by: |
| + | **Number of infected [[Suborder: Metastigmata, ticks|ticks]] seeking a blood mean ('''tick pressure''') |
| + | **Calves under 9 months are refractory to disease |
| + | ***Can develop immunity if exposed without showing clinical signs |
| + | **Premunity developes quickly in infected cattle which causes a 'carrier state' |
| + | **Immunity can wane in the absense of re-infection |
| + | **Uninfected cattle remain susceptible |
| + | |
| + | *Enzootic Instability |
| + | **Low rate of transmission |
| + | **Few infected [[Suborder: Metastigmata, ticks|ticks]] |
| + | **Infrequent exposure |
| + | **Immunity wanes or is completely absent in many individuals |
| + | **Low levels of herd immunity |
| + | **'''Higher''' incidence of disease |
| + | |
| + | *Enzootic Stability |
| + | **High rate of transmission |
| + | **Many infected ticks |
| + | **Frequent exposure boosts immunity |
| + | **High level of herd immunity |
| + | **'''Lower''' incidence of disease |
| + | |
| + | *Predisposing factors: |
| + | **Sucseptible animals introduced into an infected area |
| + | **Infected [[Suborder: Metastigmata, ticks|ticks]] are intorduced into a clean area |
| + | **Infected cattle are introduced into an area with clean [[Suborder: Metastigmata, ticks|ticks]] |
| + | **Temporary reduction in the [[Suborder: Metastigmata, ticks|tick]] population decreasing the transmission rate (causing enzootic instability) |
| + | **Infected are transported or stressed in other ways, e.g. parturition |
| + | |
| + | *In the UK: |
| + | **Sporadic disease |
| + | **Enzootic instability |
| + | **Occurs mostly during the spring and autumn during periods of greatest [[Suborder: Metastigmata, ticks|tick]] activity |
| + | **Occurs mostly in stressed cattle under 2 years old on rough grazing |
| + | **''B. divergens'' the most common species |
| + | **[[Suborder: Metastigmata, ticks#Ixodes spp.|''Ixodes ricinus'']] is the vector |
| + | **[[Suborder: Metastigmata, ticks#Disease Transmission|Trans-ovarial]] transmission to the next generation occurs |
| + | **''B. major'' occurs in South East England but is not pathogenic |
| + | ***Vector is [[Suborder: Metastigmata, ticks#Important Hard Ticks|''Haemaphysalis'']] |
| | | |
| ==''Theileria''== | | ==''Theileria''== |