Ways we can simplify diagnostic sampling for infectious diseases

Monday, August 9, 2010

FTA® cards and collection of oral (saliva) fluids with ropes hung in pens both have the potential to simplify collection and transportation and storage of samples, while reducing cost and maintaining accuracy

by S. ERNEST SANFORD

Techniques are being developed to speed up the collection and transportation of samples to the laboratory for diagnostic tests, at less cost, while still maintaining accuracy for diagnostic testing. These include the collection of oral fluids (saliva) using ropes hung in pens and FTA® cards for transport and storage of samples.

I have written previously on collection of oral (saliva) fluids with ropes hung in pens for the pigs to chew on (Better Pork, October 2006 and June 2009), so I shall only briefly review the rope collection saliva technique here and will concentrate this time on FTA® (Flinders Technical Associates) cards.

Tests can be run on oral fluids to identify many disease agents, such as PRRS virus (PRRSV), PCV2, swine influenza virus (SIV), Mycoplasma hyopneumoniae (Mhyo) Actinobacillus pleuropneumoniae (APP) and many other pathogens. Tests can also be done on saliva to determine levels of antibodies (Abs) to these agents.

The collection of oral fluids is accomplished simply by hanging a cotton rope in the pen for the pigs to chew on over a 30-40 minute (or longer, if desired) period. The rope is then placed in a plastic bag and the fluids squeezed out into the bag, the lower corner end of the bag snipped and the fluids emptied into tubes and submitted for various laboratory tests. Laboratory tests that can be conducted include polymerase chain reaction (PCR), virus and bacterial isolations, and ELISA and other tests for Abs.

Several benefits derive from oral fluid collection by ropes. It is non-invasive (requiring no needles), involves less labour, and can be used to sample a larger percentage of a herd. It costs less than other methods because there are no needles, few collection tubes, and it poses less chance of injury to workers and pigs. It is also good for whole herd surveillance for new and endemic diseases.

FTA® cards are developed by Whatnan plc laboratories in the United Kingdom and are made of filter paper with a cellulose-based matrix material containing embedded chemicals that lyse (destroy) cells in the sample while preserving the nucleic acids (DNA and RNA). The chemicals inactivate bacteria and viruses deposited on the FTA® cards, making them non-infectious and therefore safe to transport in regular mail or via couriers. 

These features also make it possible to transport samples containing highly infectious disease agents and samples from animals with foreign animal diseases, like hog cholera and foot-and-mouth disease. FTA® cards can be shipped and stored at room temperature with no degradation of the embedded nucleic acids. Overall, these FTA® cards are extremely valuable for transportation and storage of clinical samples in a safe, non-biohazardous manner suitable for molecular diagnostics.

FTA® cards have been used in industry, human and veterinary medicine for many years.  They have revolutionized many industries that depend on high quality purified genetic material. In veterinary medicine, they have facilitated transportation of Newcastle and FMD viruses but, apart from limited exchanges between research laboratories, they have been largely ignored or have been unknown in the swine field. That's about to change.

Now that we are doing so much PCR testing for identification of swine pathogens, these cards can greatly simplify the movement of samples from the veterinarian to the laboratory for testing. They will reduce costs and markedly simplify the mailing and transportation process. 

Oral fluids by rope and transportation and storage on FTA® cards will have an important role as we move forward with PRRS Area Regional Control & Eradication (ARC&E) projects. A massive amount of sampling and laboratory testing will have to be done for herds in an ARC&E project. Oral fluids and FTA® cards will both be used to simplify collection and transportation and storage of samples. Furthermore they will reduce costs, simplify and make sampling easier and increase safety while maintaining diagnostic accuracy. 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