A study was published this Month in JVIM entitled “Vaccination and Seasonality as Risk Factors for Development of Meningoencephalitis of Unknown Origin in 172 Dogs”. I don’t know about you, but this is a super-hot topic in my world, so I immediately thought we needed to get this into a TidBit Tuesday!
Overview
MUO (meningoencephalitis of unknown origin) is a clinical diagnosis based on MRI findings, identification of a mononuclear pleocytosis and negative infectious disease testing. The authors proposed to investigate the association between vaccination WINDOW and the development of MUO. What is a vaccination window? A vaccination window is a categorization of the time from most recent vaccination to onset of clinical signs (that were later diagnosed as MUO) that was placed in 45 or 90 day intervals for analysis. For example, there was a window of 0-45 days and 46-90 days. Additionally, the authors evaluated the presentation season.
Results
172 dogs were included in the 2 year prospective study. The median age at onset of clinical signs was 5 years (range 0.18-15.3 years). Interestingly, Labrador and Labrador-X dogs were most common (13/172) followed by French Bulldogs and then Chihuahua/Chihuahua X. This should be a reminder that MUO can affect anyone, regardless of breed, age, sex, and size. It should always be on your differential diagnoses list for dogs with neurologic disease!
More dogs received vaccinations within 450 days of the onset of signs, so >450 days was considered “referential” for analysis. Looking specifically at dogs vaccinated within 450 days of the development of MUO, the highest risk for development of MUO was associated with vaccination in the first 45 days after vaccination (9x higher). This was not a case-control study, so we don’t know what the incidence of development in a breed or time. All that the authors are stating is that of the dogs with MUO that had received vaccination within 450 days of the development of signs, being vaccinated within 45 days resulted a 9x higher risk of developing of MUO.
The type and number of the most recent vaccinations administered was also evaluated. The number of vaccinations administered ranged from 1-7, median 4, in all dogs with MUO. NO association with the type (Bordetella vs distemper, etc.) or number of vaccinations administered at one time was associated with the development of MUO.
Lastly, there was no associated with the season and the development of MUO.
Take home message:
Dogs get MUO frequently so keep it on your differential diagnoses list
Dogs who develop MUO have a 9x higher chance of developing it within 45 days of vaccination. (This doesn’t mean that dogs have a 9x higher chance of developing MUO overall!)
MUO is not apparently linked to season
We need to learn a lot more about MUO but likely there is a genetic risk that is triggered by something and that something might be vaccination.
If you found this article interesting and would like to read the entire thing it can be found at https://onlinelibrary.wiley.com/doi/10.1111/jvim.70013.
Thanks for reading! I hope you have a great week and look forward to working with you very soon.