Topical farm disease (midges) Flashcards
What species of diptera are midges?
Culicoides spp
Culicoides transmit many pathogens and are an important vector species of which 3 diseases?
Bluetongue
Schmallenberg
African Horse Sickness
(Equine encephalosis)
Which midges bite? Why?
Females only - need protein from blood for fertility and egg development
Males only for mating
Where do females lay eggs?
Substrate - dung or soil depending on species
How do culicoides transmit viruses?
Develop in infected animal dung
Developed adult feeds on animal and infects the
Why do different species need different control methods?
Different breeding sites
What is a natural control method for Culicoides?
Mermithid nematodes
How do Mermithid nematodes kill culicoides?
Develop inside midge larvae
Kill on emergence
If remain inside adult, cause sterilisation
What is significant about Bluetongue, Schmallenberg and African horse sickness?
All notifiable disease
What animals does blue tongue infect? Which species does it cause severe disease?
Ruminants
Severe in sheep (milder in cattle - subclinical, lower mortality)
What type of pathogen causes Bluetongue?
RNA virus
Why is it difficult to produce a vaccine against RNA viruses?
They are unstable so mutate quickly
What species act as a reservoir for Bluetongue?
Cattle
Often subclinical but can get clinical disease
What are the symptoms of Bluetongue?
Swelling of head, mouth, neck Drooling at mouth Eye/nasal discharge Pyrexia Cyanotic tongue (rare)
How is Bluetongue transmitted?
Mainly vector bourne
Also via semen, live vaccines and blood
There are both modified live and inactive live vaccines for Bluetongue. What are there advantages/disadvantages?
Modified - cheaper, immunity after one vaccine
Inactive - expensive, need multiple vaccines
Is the Bluetongue virus easy to control? How is it best controlled?
No
Control by Culicoides midges
What virus causes Schmallenberg?
RNA virus
What animals is Schmallenberg infectious to?
Ruminants
Severe in horses - high mortality
What are the symptoms of Schmallenberg virus?
Abortion
Fever
Schmallenberg and Bluetongue are very siimilar. What are the 4 main differences?
BTV - can be detected, low infection rate of vectors, long incubation period, long viraemia
SBV - silent spread, high infection rate of vectors, short incubation period, short viraemia
What virus causes African horse sickness?
Arbovirus
Why do outbreaks of African horse sickness occur every 10-20 years?
New population of horses
Not immune
What are the 3 forms of African horse sickness?
Cardiac
Pulmonary
Mixed
