Today, Dr. Albert Rovira from the University of Minnesota, Veterinary Diagnostic Laboratory shares with us the trends he has observed in PRRSV diagnostics over the past years. The findings can be found in the slideshow below.
- The use of tissue samples follows a seasonal pattern and represents clinical cases with a percent of positives of 30%
- The number of oral fluid samples is increasing. Used for monitoring positive farms and more recently for surveillance in negative farms as well:: 15% of positive samples
- The number of blood swabs, serum samples, and semen samples, typically used for surveillance in negative farms, is decreasing. Lowest percent of positive samples: 8%
- RFLP patterns are changing over time. In the past years, 1-7-4 > 1-3-4 or 1-8-4 or 1-4-4
Reminder: what is a RFLP pattern?
RFLP stands for Restriction Fragment Length Polymorphism and is a technique used to detect nucleotide changes in a genetic sequence. The genetic material is put in contact with restriction enzymes which are very specific to a genetic sequence. If the enzyme recognizes the sequence pattern, it will cleave the DNA or RNA fragment. After that, a type is determined based on the number of fragments and its size.
For example with PRRSV, three enzymes are used and the number of fragments each of them produces makes up the numbers of the RFLP pattern. Currently, the RFLP type is not actually performed in the lab. Instead, it is predicted based on the ORF5 RNA sequence and the knowledge of the cutting capabilities of each enzyme.
Therefore, the RFLP pattern gives us a way to cluster PRRSV strains in groups but very little indication about how similar they are to each other.