Two recent studies show the time is near to tackle a trichinae-free certification program.
Trichinella spiralis, a tiny nematode parasite found in muscle tissue of many warm-blooded animals, remains as a persistent concern for the pork industry. More commonly referred to as trichinae, this pesky parasite's occasional occurrence in pork has resulted in a host of further processing requirements set forth by the USDA's Food Safety and Inspection Service (FSIS) plus instructions to "cook pork thoroughly."
There's no way to know the impact trichinae has had on domestic markets, but as recently as 1994 it was still the leading pork-related question of callers to the USDA's Meat and Poultry Hotline.
Most countries have inspection programs for trichinae. The U.S. does not. Therefore, when we export to those countries, we must follow their trichinae inspection requirements.
History tells us that at one time there were good reasons for people to be concerned about trichinae. A National Institute of Health report published in 1943 found one out of every six people in the U.S. were infected (16.1 "percent"). A similar study in 1970 showed the prevalence had fallen to 4.2 "percent".
While actual infection rates are important, most cases are subclinical. Clinical cases of trichinellosis (the name of the disease in humans) are reported to the Centers for Disease Control. Clinical cases have shown a similar decline, from 404.5/year between 1947 and 1950 to 113.4/year between 1966 and 1970, to the current rate of 38.3/year from 1991 to 1996. Only 13 cases of human trichinellosis were reported in 1996.
Studies in pigs have shown a similar decline in prevalence, but it is important to realize that pork is not the only source of human infections. Many are caused by game meats (see diagram).
At the turn of the century, greater than 2.5 "percent" of pigs tested had trichinae. This number declined to 0.95% in the 1930s, 0.63 "percent" in 1948-1952, 0.16 "percent" in 1961-1965 and 0.12 "percent" in 1966-1970. Testing of sera drawn during the National Swine Survey in 1995 gave an infection rate of 0.013 "percent". Thus, infection rates for trichinae in pigs are now extremely low.
The dramatic declines in trichinae in pigs and trichinellosis in humans are related and reflect the changes in the industry. Major inroads were made into trichinae infection with the advent of garbage cooking laws passed for vesicular exanthema (1953-1954) and the hog cholera eradication program (1962). Of equal importance has been the movement to high levels of biosecurity and hygiene under which most pigs are now raised.
Despite the fact that trichinae are rare today, pork still suffers from its legacy. It's a question of perception versus reality. Dramatic declines in prevalence in pigs and the extremely low numbers of cases in humans are largely unrecognized by consumers. They still raise questions about "worms in pork."
And, the fact remains, the lack of any control programs for fresh pork creates problems in international markets despite the extremely low prevalence.
To address the trichinae issue, a committee of National Pork Producers Council (NPPC), government agencies (USDA's Agricultural Research Service, Animal and Plant Health Inspection Service and Food Safety and Inspection Service) and private sector representatives has been conducting a series of research studies to come up with a system to document the absence of trichinae in pigs. This effort, called the National Trichinae Research Project, has been underway for three years and is now nearing conclusion. The following summarizes some of the findings.
Trichinae Research Project >From 1995-1996, the committee conducted the Northeast Trichinae Study. The goals were two-fold:
* To test the ELISA method (a rapid blood test) for its ability to detect trichinella-positive farm pigs, and
* To identify risk factors associated with trichinella-positive farms.
The studies, conducted in New Jersey, Connecticut, Rhode Island, Massachusetts, Vermont and New Hampshire, tested pigs from 156 farms. Farms tested varied based on size, type of facility (e.g., farrow-to-finish, finish only), feed type and management. A questionnaire was completed and blood samples drawn on each farm.
Of the 4,078 pigs tested, we found 15 positive animals (0.37%) representing 10 farms. In some cases we were able to go back to tested animals and collect tissues to determine intensity of infection. In all cases, infection levels were very low; none of the animals found positive would have posed a public health risk.
This study showed the ELISA test was a good indicator of infection on farms with a high level of sensitivity. Importantly, despite a low level of prevalence of trichinae in the areas tested, there were no pig infections of public health concern.
Infection of pigs can only occur by eating meat containing infective stages of the parasite. Historically, feeding uncooked garbage, poor hygiene and close contact with rodents is associated with trichinae in pigs.
In the Northeast study, significant risk factors were limited to exposure of pigs to wildlife with only marginal association of infection with rodent exposure. No correlation was found with waste feeding.
We learned several things from this initial study:
* Trichinae infection is rare and at a very low level when found,
* The ELISA is a quick and reliable test that can be used to screen herds for infected animals, and
* Risk of infection to pigs is limited to a few, easily controlled risk factors (see "How to prevent trichinae in pigs," page 32).
The next step was to establish a system in which freedom from infection in pigs could be documented. In Europe and many other countries, each pig is tested at slaughter by digestion of a small portion of tissue. By doing this for decades, many countries have removed most trichinella from pigs.
In contrast, the U.S. has never had an inspection program. However, because most U.S. producers do such a good job of raising pigs under hygienic conditions, we have made almost as much progress in eliminating infection. To develop a means to substantiate this progress, the next trichinae study looked at a certification process.
Iowa Certification Pilot Study The Iowa Certification Pilot Study began in April 1997. This ongoing study was designed to test the feasibility of certification as a means to document on-farm trichinae-free pig production.
The first step was to check the trichinae status of pigs representing all farms marketing through a specific packing plant. This phase, performed at Sioux-Preme Packing Company in Sioux Center, IA, used the ELISA test, and a digestion test routinely performed in Europe; 220,000 pigs were tested over a six-month period.
Participating farms were then asked to participate in the study's second phase. This phase includes a farm audit developed by members of the Trichinae Working Group with expertise in epidemiology and risk verification. This is the most critical part of the certification process.
The audit, containing questions about general farm management, biosecurity, feed and feed storage, rodent control programs and general hygiene requires about an hour to complete. Audits will be administered by accredited veterinary practitioners and APHIS field personnel.
When the estimated 250 farm audits have been completed, scores will be assigned based on knowledge of risk for transmission of trichinae.
Producers scoring at or above a certain level will be notified that their production practices already meet the criteria for trichinae-free certification. Those scoring below the cutoff will be notified and suggestions made for management changes that would increase the score to above the certification cutoff.
Up to 85 "percent" of producers should meet certification requirements with no changes. Most others will be able to make minor changes to reach a certification level on audit score.
The Iowa Certification Pilot is scheduled to conclude during the early part of 1998. Follow-up steps will be taken to maintain continuity with the producers participating in the certification audit. Some seasonal variations in audit scoring did show up, so the study may be extended to learn more about those differences.
And, due to the very low prevalence of trichinae in Midwestern pigs, an additional pilot study will likely be performed before this system is used widely.
The Trichinae Working Group is considering an additional "certification trial" in another part of the country. This next phase will be much shorter and will target high-risk herds.
The purpose of the next phase is to challenge the integrity of the system. A combination of auditing and testing will be conducted to assure that herds at risk, or those with infected pigs, do not slip through on the standards established in the audit. This is the final step in validating the certification process as a viable mechanism for producing trichinae-free pigs.
Trichinae-Free Certification Researchers are anticipating success in the final phase for several reasons:
* Prevalence of trichinellosis is extremely low and remaining problem areas and herds can be easily identified.
* Strategies for eliminating risk are simple and easily implemented.
* Tools for assessing lack-of-risk factors under most management systems and for monitoring both the process and the product are available.
If successful, trichinae-free production practices can be put in place that will have a major impact on pork's image domestically and internationally.
The overall certification process will include the following elements:
* Accredited veterinary practitioners, trained in good production practices relative to trichinae, will work with producers to assure that risks are minimized in production systems. Regular farm audits will document absence of risk.
* Periodically, some pigs are tested to verify the absence of infection. Since the system is based on a pre-harvest, HACCP approach, only a sample of production needs to be tested.
Testing can take place by collecting samples at slaughter so on-farm sampling is not necessary. Tools that can be used to verify the absence of infection (e.g., ELISA) have been extensively tested.
* Third-party monitoring of certification is necessary for integrity of the system. By periodic checks on the auditing process and spot testing, APHIS will serve a role in providing oversight of the certification process.
Efforts to certify pork free from trichinae should have an immediate impact on international markets by producing a product that is competitive with countries that currently inspect for trichinae.
We can't catch up by starting now to test pigs at slaughter. We can, however, initiate a better approach to food safety by implementing a system at the farm that is superior to individual animal testing. In addition, implementation of a trichinae certification system will provide an infrastructure for tackling more complex issues in on-farm certification.
In the domestic market, the issue of trichinae is primarily one of perception because infections are so rare. However, changing public perception requires education regarding the safety and absence of the parasite in the pork supply.
Trichinae have long been a stigma to the U.S. pork industry. With a minimum of effort from producers, packers and government officials, it may be possible to put this issue to rest.
Risk factors for transmission of trichinae to pigs are limited. To become infected pigs must eat meat containing infective stages of the parasite.Taking steps to avoid exposure is simple and can assure little or no risk for ex posure of pigs:
1. Don't feed uncooked waste products, table scraps or animal carcasses to pigs. This is particularly important in the case of carcasses from hunted or trapped wildlife. 2. Eliminate or minimize exposure of pigs to live wildlife. Create barriers that are effective in separating pigs from skunks, raccoons and other small mammals. 3. Implement and maintain an effective rodent control program. Bio-security, maintaining perimeters, baiting and trapping are all part of rodent control. Maintain good hygiene. Remove dead pigs as soon as they are found. Keep barns free from clutter and feed stored securely.
Additional information on rodent control is available in Pork Industry Handbook Bulletin PIH-107. Write Pork Industry Handbook, Media Distribution Center, 301 South 2nd Street, Lafayette, IN 47901-1232. Additional information is available from the National Pork Producers Council (515-223-2600) or from your veterinarian.