Innovative adaptations of oral fluids technology

Thursday, October 10, 2013

Researchers are uncovering uses for oral fluids/rope technology never dreamed of by its discoverer. One is to 'vaccinate' PRRS-naïve replacement gilts for PRRS

by S. ERNEST SANFORD

I have written on oral fluids technology several times before in this column. This time it will be oral fluids used in reverse, as I report on applications of the oral fluids/rope technology being adapted and put to use by some very progressive thinkers to deliver materials to the pigs, rather than taking materials from them.

Instead of ropes being used to get oral fluids from the pigs to provide samples for diagnostic tests, the ropes in these cases are soaked in a product, then presented to the pigs for them to chew on and thereby deliver the product to an entire population of pigs!

Here are a few examples of this very innovative application that I've been calling "reverse oral fluids/rope technology." They were presented by researchers at the annual American Association of Swine Veterinarians (AASV) conference held in Denver, Colo., in March 2012.

Dr. Darwin Reicks and co-researchers used ropes to "vaccinate" PRRS-naïve replacement gilts for PRRS. Before doing the actual "vaccination," they did a small pilot study to determine what would be the best material to put on the ropes along with vaccine to encourage better sucking on the ropes by the gilts. They tried four different materials and determined that maple syrup gave the best uptake by the gilts.

They then soaked ropes in modified live PRRS vaccine and maple syrup and presented the ropes to one of four groups of replacement gilts, 10 pigs per group. One group consisted of the gilts presented to vaccine-soaked ropes and challenged with PRRS virus (PRRSV). A second group was intramuscularly injected with vaccine and challenged. A third group was injected with saline and challenged (positive control group), while the fourth group was injected with saline and not challenged (negative control group). Sera from all pigs were then checked repeatedly over the next 28 days by polymerase chain reaction (PCR) for PRRSV and for seroconversion to PRRSV.

PCR confirmed that most of the vaccine-injected pigs became viremic and seroconverted to PRRSV, as did the saline-injected and challenged pigs (positive controls). The negative control pigs remained negative throughout the experiment. The rope-vaccinated pigs did not become viremic and did not seroconvert to PRRSV. So, in this study, the vaccine-saturated ropes did not "vaccinate" the naïve gilts.

In a somewhat similar vein, another study by Abigail Rodalen, a veterinary summer student at the University of Minnesota supervised by a swine veterinary professor, soaked ropes in ziplock plastic bags each containing 120 millilitres of serum taken from PRRSV-viremic pigs and diluted with a buffering solution. The ropes were then hung in a pen with 30 PRRSV-naïve replacement gilts.

A second group of 30 PRRSV-naïve gilts was injected directly with two millilitres each of the same serum. By 21 days after implementing the above procedures, all pigs in both groups were viremic and had seroconverted to PRRSV. So in this study, using actual PRRSV rather than vaccine virus, the pigs were infected with PRRSV. It suggests that, with some refinement of the vaccine-delivery technique, it might be possible to "vaccinate" pigs using the rope technique.

In the third of these innovative "reverse rope" procedures presented at the 2012 conference, Emily Kuntz, another veterinary student this time at the University of Illinois, along with two supervising swine veterinarians, used ropes soaked in oral fluids from gilts confirmed with Mycoplasma hyopneumoniae (Mhyo). These ropes were then used to acclimatize weaning-age pigs to Mhyo. The ropes were presented to 10 weaned Mhyo-naïve pigs. Another group of 10 weaned naïve pigs was left as unexposed controls. The exposed pigs developed acute respiratory and neurological signs and four of the 10 pigs died. Diagnostic examinations confirmed Glässer's disease. The unexposed control pigs remained normal.  

Now, two of these three innovative efforts proved unsuccessful and one of the two unsuccessful efforts resulted in morbidity and death of 40 per cent of the pigs. I feel certain, however, that this is not the end of the line for extending this new "rope technology" into areas we have not yet even dreamed of. The researchers will refine their techniques and modify their approaches to get them right for these and other innovative ways of using the ropes never conceived of by Dr. Jeff Zimmerman, the originator of this rope technology. BP

S. Ernest Sanford, DVM, Dip. Path., Diplomate ACVP, is a swine specialist with Boehringer Ingelheim Vetmedica (Canada) in Burlington. Email: ernest.sanford@boehringer-ingelheim.com