Trichinellosis, a disease caused by infestation of parasites belonging to the genus Trichinella, has now become sporadic thanks to the capillarity of official public controls and the greater attention to avoiding the consumption of raw or undercooked meats of the equine, swine and wild boar species.
It is one of the zoonoses monitored in all member countries. The countries most affected in 2018 were Bulgaria and Romania, which reported 45 and 25 cases of human trichenellosis, compared to only two cases notified by Italy (EFSA, ECDC, 2019).
Trichinella, the invisible parasite
Trichinella it is a round worm (nematode) which carries out most of its life cycle in some animal species, which, despite being infested, do not show clinical signs of disease. The parasite engraves itself in the muscle fibers of carnivorous or omnivorous animals, which infest themselves by feeding on the meat of parasitized subjects. Humans are infested mainly by ingesting raw or undercooked meats of suids (pigs and wild boars) but the parasite is also found in the muscles of foxes, wolves, raccoons, bears, lynxes and mustelids (EFSA, 2011).
T. spiralis - widespread mainly in pigs and wild boars, rare in other carnivores - it is the best known of the four species of Trichinella present in Europe, as well as being the most pathogenic species for humans. The species T. native it is mainly present in wild carnivores in Northern Europe, while T. britovi it is widespread both in wild carnivores and in suidae. In the end, T. pseudospiralis it infests both mammals and birds (carnivores and omnivores), is widespread in various areas of the old continent but is rare in Italy (Ministry of Health, 2020).
Horse, pork and wild boar meat, cook with care
Several outbreaks of trichinellosis due to the consumption of horse meat were reported between 1975 and 2005 both in France and in Italy, the only European countries where horse meat is consumed raw. On closer inspection, the horse should not be among the endangered species, as a herbivorous animal. However, horse meat, especially that of Eastern European animals, has represented a danger for the consumer for decades. Probably, as reported by the Istituto Superiore di Sanità, because they are fed with mash containing leftovers from the slaughter of pigs.
Eating habits therefore strongly affect the spread of human trichinellosis, as the consumption of raw horse meat - as well as the consumption of raw pork and wild boar (fresh sausages, salami) or undercooked - increases the risk of transmission to the consumer.
Trichinellosis, the risks for humans
The larvae encysted in the meat of suidae or horses, following their consumption by humans, they are released in the human stomach and cross the wall of the small intestine, where they develop into adult larvae. The females generate new larvae which, through the lymphatic vessels, reach the muscular tissues, where they are localized giving rise to the tissue cysts. After months or years, the cysts can undergo calcification (Gottstein et al., 2009).
The infestations da Trichinella in humans they can be silent if the ingested larvae are few. However, in most cases, trichinellosis begins with gastrointestinal disorders, fever and weakness, followed by muscle and joint pain, breathing difficulties, and serious complications, such as myocarditis. In some cases, periorbital or facial edema and subungual hemorrhages (under the nails) also occur. Fatal cases are rare and are linked to massive infestations accompanied by clinical complications (Gottstein et al., 2009). Systemic symptoms usually appear 8-15 days after ingestion of the meat containing the cysts Trichinella (EFSA, 2011).
Official public controls
Control di Trichinella it is mandatory, at European level, in the slaughterhouses of sensitive animal species, such as pigs and horses. Wild boar meat - which currently represents the main vehicle of Trichinella - are subject to mandatory control. Regulation (EU) no. 2015/1375 prescribes the sampling and research of the larvae on a muscle portion on all carcasses of pigs, horses and wild boars. Only pigs reared in controlled housing conditions, certified Trichinella-free, are exempted from the systematic control in the slaughterhouse, which is therefore carried out on 10% of the animals rather than on all of them.
The capillarity controls ensures the identification of parasitic animals. Suffice it to say that in 2018 across Europe no pigs raised in biosecurity conditions tested positive, while the positivity affected only 0,0002% of pigs from non-farmed farms. Trichinella free. This percentage rises to 0,09% in hunted wild boars and 1,6% in foxes (EFSA and ECDC, 2019). The carcasses of animals infested with Trichinella they are declared unfit for human consumption and must be destroyed.
Silvia Bonardi
REFERENCES
1) EFSA, European Food Safety Authority (2011) Scientific Report on Technical specifications on harmonized epidemiological indicators for public health hazards to be covered by meat inspection of swine. EFSA Journal 2011; 9 (10): 2371. [125 pp.] Doi: 10.2903 / j.efsa.2011.2371.
2) EFSA, ECDC (European Center for Disease Prevention and Control) 2019. The European Union One Health 2018 Zoonoses Report. EFSA Journal 2019; 17 (12): 5926, 276 pp. https://doi.org/10.2903/j.efsa.2019.5926
3) Gottstein B, Pozio E, Nöckler K (2009). Epidemiology, diagnosis, treatment, and control of trichinellosis. Clinical Microbiology Reviews 22, 127–145. doi: 10.1128 / CMR.00026-08. PMID: 19136437; PMCID: PMC2620635
4) Reg. (EU) 2015/1375, defining specific rules applicable to official controls relating to the presence of Trichinae in meat. Consolidated text as of 14.10.20 on https://eur-lex.europa.eu/legal-content/IT/TXT/?uri=CELEX%3A02015R1375-20201104
Graduated in Veterinary Medicine and Specialist in Inspection of Food of Animal Origin and in Veterinary Public Health, she is Professor of Inspection and Control of Food of Animal Origin at the University of Parma.
