Comparison of trichinelloscopy with a digestion method for the detection of Trichinella larvae in muscle tissue from naturally infected pigs with low level infections

A review of testing and assurance methods for Trichinella surveillance programs

While global cases of trichinellosis have fallen since pork regulation began, the disease remains a danger to pork and animal game consumers as well as a liability to producers. Managing food safety risk and supporting agricultural trade requires cost-effective and sensitive diagnostic methods. Several means exist to inspect pork for parasitic infections. Here, we review literature concerning the sensitivity, specificity, and cost of these methods. We found that artificial digestion coupled with optical microscopy to be the best method for verification of Trichinella larva free pork due to its cost efficiency, high specificity, and reliability. Serological techniques such as ELISA are useful for epidemiological surveillance of swine. While current PCR techniques are quick and useful for diagnosing species-specific infections, they are not cost efficient for large-scale testing. However, as PCR techniques, including Lateral Flow- Recombinase Polymerase Amplification (LF-RPA), improve and continue to reduce cost, such methods may ultimately succeed artificial digestion.

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We compared cost, sensitivity, and specificity of available and foreseeable tools.

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The magnetic stir bar method remains the gold standard for Trichinella surveillance.

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Serological methods miss early infections but offer promise for use in surveillance.

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Isothermal methods offer future promise given their speed, accuracy, and ease of use.

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Genetic methods are uneconomical but advances have promise to reduce cost.

Survey of Trichinella infections in domestic pigs from northern and eastern Henan, China

The aim of this work was to investigate the current situation of Trichinella infections in swine in the cities of Anyang and Shanqiu in the Henan province historically designated as trichinellosis-free. A total of 475 diaphragm muscle samples were collected from 2010 to 2011 and examined by trichinelloscopy and artificial digestion. No Trichinella larvae were detected by trichinelloscopy; however, using the digestion method, 3.79% (18/475) of domestic pigs were deemed positive for Trichinella. Among the 475 pigs examined, 112 from an industrialized pig farm were negative. However. Trichinella larvae were detected in 10% (9/90) of pigs from small pig farms, which was significantly higher than the 3.3% (9/273) of pigs found positive from backyard farms (P<0.05). The larval burdens in infected animals ranged from 0.1 to 1.58 larvae per gram. The larvae were identified by multiplex PCR as Trichinella spiralis. Our study confirms the existence of porcine trichinellosis in northern and eastern parts of Henan. The results will be useful for evaluating the risk of infection for humans. Given this new found data, public health officials should consider implementing strategies to eliminate human transmission.

Comparison of artificial digestion and Baermann's methods for detection of Trichinella spiralis pre-encapsulated larvae in muscles with low-level infections

Artificial digestion method is widely used for the detection of Trichinella larvae (mainly the mature larvae, e.g., encapsulated larvae in encapsulated Trichinella) in meat. The previous studies demonstrated that Trichinella spiralis pre-encapsulated larvae (PEL) at 14-18 days postinfection (dpi) had the infectivity to new hosts. However, to our knowledge, there is no report on the detection methods of PEL in meat. The purpose of this study was to compare the efficiency of artificial digestion and Baermann's methods for detection of T. spiralis PEL in meat, and to test the factors affecting the sensitivity of the two methods. Forty-five male Kunming mice were randomly divided into 3 groups (15 mice per group), and each group of mice was orally inoculated with 20, 10, or 5 muscle larvae of T. spiralis, respectively. All infected mice were slaughtered at 18 dpi, and the muscles were minced. The digestion method that was recommended by International Commission on Trichinellosis and Baermann's method were used to detect the PEL in the infected mice. The detection rate of PEL in both mice infected with 20 muscle larvae by digestion and Baermann's method was 100% (15/15); the detection rates of PEL in mice infected with 10 larvae by the two methods just mentioned were 93.33% (14/15) and 100% (15/15), respectively; when the mice infected with 5 larvae were tested, the different detection rate of PEL was achieved by using digestion method (63.33%) and Baermann's method (100%). Additionally, the number of PEL collected from the mice infected with 20, 10, or 5 larvae by Baermann's method was greater than that by digestion methods. The mortality of PEL increased along with the prolongation of digestion duration, because the PEL were not resistant to enzymatic digestion. The results revealed that the Baermann's method is superior to the digestion methods for detection of T. spiralis PEL in muscle samples with low-level infections.

Sensitivity and optimization of artificial digestion in the inspection of meat for Trichinella spiralis

In many countries, the method of choice in inspecting meat for Trichinella spiralis infection is artificial digestion. We conducted a study of the sensitivity of the artificial digestion method recommended by the International Commission on Trichinellosis for detecting T. spiralis larvae in meat and of the effect of modifications of some procedures used in the method on its sensitivity. As part of this, we evaluated the effects on larval recovery of the vessels used for larval settling, sieve sizes, and temperatures at which larvae passed through the sieves, using larvae from T. spiralis-infected mice. We observed the effects on larval recovery of digestion duration and of modified artificial digestion by using 10-g samples of infected mouse muscle alone or mixed with uninfected pork. The percentages of larvae recovered with the respective use of separatory funnels and conical cylinders were 51.20% and 98.70%. The rates of recovery of T. spiralis larvae at 4 degrees C after passage through sieves of 425-microm mesh (No. 40), 250-microm mesh (No. 60), and 180-microm mesh (No. 80) were 98.42%, 90.59%, and 81.63%, which exceeded the 97.79%, 85.10%, and 61.12% rates of recovery of motile larvae at 40 degrees C and the 95.12%, 78.60%, and 44.16% rates of recovery of dead larvae at 90 degrees C. The larval recovery rate after digestion for 2 hours (96.18%) was greater than that after 0.5 hours (88.00%). We then examined a modified digestion method in which 10-g samples of pork mixed with 300 mL of digestive solution were digested for 2 hours at 43 degrees C followed by chilling of digest solution to 4 degrees C before passing it through a 425-microm mesh (No. 40) sieve and allowing it to settle in a 1-L conical cylinder. With this procedure, the modified method detected T. spiralis in samples of pork meat weighing 10 g and containing either 1 larva per gram or 0.1 larva per gram. Further validation of digestion method incorporating these modifications is required with the use of larger samples of infected muscle from species such as swine, which are routinely tested for T. spiralis for the purpose of food safety.

Histopathology of trichinellosis in wild boar

Histopathological study of Trichinella constitutes an important knowledge base to understand the pathogenesis of this disease. This study analyses cell response and macroscopic lesions in wild boar for the two species of Trichinella present in Spain: Trichinella spiralis and T. britovi. We carried out both trichinelloscopy and artificial digestion to calculate the parasitic load and relate this to the macroscopic lesions. The results obtained prove a lesser adaptation of T. britovi in wild boar. From a histological point of view, the organic region that was most affected was the skeletal muscle, where inflammatory infiltrates were observed around the larvae, and they were most abundant in calcified cysts.

The effect of pest control on the incidence of trichinosis in Virovitica-Podravina County, Croatia

The aim of the study was to assess the role of pest control as a preventive measure in the control of trichinosis. The investigation was designed as a retrospective cohort study in the Virovitica-Podravina County. The incidence of trichinosis was determined according to the presence or absence of exposure to protective pest control measures. Differences in the rate of trichinosis infection were determined by calculating relative risk (RR), i.e., the ratio of absolute risk in the two groups. In this epidemiological study, data collected in the County area regularly covered by pest control (exposure area) were compared with other areas not covered by regular pest control measures (non-exposure area). The study included 132 subjects living in the County and locally infected with trichinosis. Patient data were obtained from their medical history, epidemiological survey and epidemiological questionnaire on the source (autochthony) of the disease. The study also included 133,028 domestic pigs, 875 wild animals (mostly wild boar) and 111 trapped rats. All samples were examined by the method of trichinoscopy at authorized veterinary institutions of the County. Trichinosis infection was recorded in 1012 of 79,534 domestic pigs in the area exposed to pest control measures and in 51 of 53,494 domestic pigs from the rest of the County. RR for the exposure area vs. non-exposure area was 13.35 (95% CI 10.08-17.68; p<0.05); according to particular areas, RR was 3.66 (95% CI 2.62-5.13) for Pitomaca, 22.47 (95% CI 13.27-38.08) for Slatina and 118.89 (95% CI 29.7-476.01) for Orahovica (p<0.05 all). Domestic pigs from the County areas exposed to regular pest control measures had a 13-fold likelihood of infection recorded in pigs from County areas where pest control measures were not or were only occasionally performed. Quite unexpectedly, these results revealed a failure of pest control to reduce the incidence of trichinosis. The spread of trichinosis obviously occurs by some routes obviating the impact of pest control.