Influenza A virus (IAV) is one of the most frequently identified primary respiratory disease pathogens in respiratory diseases cases at the Animal Health Laboratory (AHL). IAV continues to be an area of concern in the public health arena because of the potential for zoonotic transmission of IAV from pigs to people. Much more common, however, is “Reverse Zoonoses” with transmission from people to pigs occurring. Sometimes all we need to know about IAV is whether or not pigs have been infected. In some cases we need more detailed information such as specific gene sequencing and / or virus isolation in order to design effective prevention programs such as vaccination. Based on gene sequencing, farms in Ontario have been getting hit with strains of IAV that are not usually well-covered by the commercial vaccines. In these cases we design prevention programs using autogenous vaccines made specifically for a farm, system or region.
US researchers compared various virus sampling approaches in order to detect, isolate and sequence IAV using individual samples such as nasal swabs, nasal wipes and oropharyngeal swabs, group samples such as oral fluids, surface wipes and sow udder skin wipes and environmental samples such as airborne particles deposited on surfaces and air samples. All samples were tested by IAV rRT-PCR and a subset was used for virus isolation and direct sequencing.
The researchers found that in general:
- Environmental and group samples resulted in higher odd ratios (range = 3.87-16.5, p-value < 0.05) of detecting a positive sample by rRT-PCR compared to individual pooled samples, except for oropharyngeal swabs (OR = 8.07, p-value < 0.05).
- Individual samples were most likely to yield an actual viral isolate by cell culture that could be used for gene sequencing or preparation of an autogenous vaccine.
⇒Oropharyngeal swabs in suckling pigs (78.4%)
⇒Nasal swabs (47.6%) or nasal wipes (45%) in growing pigs
⇒Udder wipes in lactating sows (75%) were the preferred samples to obtain an isolate.
Take Home Message
Environmental and group sampling strategies are the preferred diagnostic direction if the goal is just to detect infection.
Individual samples are more likely to yield live virus
Udder wipes from lactating sows appears to offer a convenient, cheap and sensitive method to monitor IAV in litters prior to weaning.
Submitted by Greg Wideman, DVM
Ref: Garrido-Mantilla J, Alvarez J, Culhane M, Nirmala J, Cano JP, Torremorell M.Comparison of individual, group and environmental sampling strategies to conduct influenza surveillance in pigs. BMC Vet Res. 2019 Feb 14;15(1):61. doi: 10.1186/s12917-019-1805-0.