Cryptosporidium spp., Toxoplasma gondii and Echinococcus spp. have been identified as important foodborne parasites in Europe.
Infection with these parasites in humans and animals, or their occurrence in food, is not notifiable in all member states. There are also no routine controls for the three parasites in food. Diseases caused by them are cryptosporidiosis, toxoplasmosis, and alveolar echinococcosis (AE) and cystic echinococcosis (CE).
The European Food Safety Authority (EFSA) described the human burden associated with these diseases as “substantial.” The agency added available data leads to an under‐estimation of the burden of infection in Europe.
The incubation period, from infection until manifestation of symptoms, ranges from a few days for Cryptosporidium to years or decades for Echinococcus spp.
Approximately 40 percent to 60 percent of T. gondii infections are considered to be foodborne and 10 percent of Cryptosporidium infections. For Echinococcus, data are uncertain, but range from around 4 percent to 40 percent for CE and 12 percent to 80 percent for AE.
Echinococcus spp., and Cryptosporidium spp. can be transmitted via the foodborne route as microscopic amounts of fecal contaminants on fresh produce and food such as molluscan shellfish. Trichinella spp. is a meat-borne parasite, and Toxoplasma can be transmitted as a fecal contaminant on fresh produce and from eating inadequately cooked meat from infected animals.
Other foodborne parasites of importance in Europe include the Anisakidae, Giardia duodenalis, and Toxocara spp, according to the EFSA panel on Biological Hazards (BIOHAZ) scientific opinion.
Taenia solium infections are considered to be of great importance on a global basis but in Europe this parasite is not thought to have a substantial impact as pigs farmed in Europe are unlikely to have access to human excrement.
The opinion looks at methods for detection, identification and tracing of the parasites in relevant foods, reviews literature on foodborne pathways, examines information on occurrence and persistence in foods, and investigates possible control measures along the food chain.
Consumer preferences for raw, fresh produce may increase the likelihood of infection as cooking inactivates all parasite transmission stages. Demand for animals raised with access to outdoor conditions, for not freezing meat prior to consumption, and eating meat raw or rare may increase exposure to infective T. gondii tissue cysts.
Whole genome sequencing may provide a solution in some circumstances but it is not always appropriate for low numbers of parasites that are hard to amplify in a contamination situation.
Echinococcus granulosus s.l. and Echinococcus multilocularis were considered to be most important in south‐eastern Europe, south‐western Europe and eastern Europe. E. multilocularis and Cryptosporidium were the most and second most important, respectively, in northern Europe and Toxoplasma and Cryptosporidium the most and second most important in western Europe.
Although as many as 17 Cryptosporidium spp. species have been associated with human infection, C. hominis and C. parvum are responsible for the vast majority of disease. Dose-response modelling predicts a probability of infection following ingestion of a single oocyst.
Symptomatic infection is characterized by diarrhea, abdominal pain, nausea or vomiting, mild fever, anorexia, malaise, fatigue and weight loss and symptoms usually last for up to three weeks.
In the ECDC Annual Epidemiological Report for 2015, the UK reported over half of all cases. Of 23 countries that reported data on cryptosporidiosis, 13 had zero to 10 cases. From 2005 to 2016, 53 cryptosporidiosis outbreaks in Europe were reported to EFSA and seven attributed to food. Outbreaks in the UK and Finland have been linked to consumption of fresh produce.
For T. gondii there are no studies to determine the dose-response for human infection. Acute illness often involves fever, headache, and enlarged lymph nodes. Outbreaks of foodborne toxoplasmosis have seldom been reported in Europe. Foodborne transmission of T. gondii is possible via consumption of undercooked meat, or unpasteurized milk from an infected animal, or as a fecal contaminant.
All three parasites can be transmitted via external transmission stages (eggs or oocysts), which are shed into the environment by infected hosts. These environmental transmission stages may contaminate fresh produce or shellfish and can remain viable and infective in such food for weeks or longer under harsh conditions. The potential for contaminated foodstuffs to act as a vehicle of infection decreases over time due to die‐off and the lack of proliferation.
Cryptosporidium oocysts are shed in the feces of infected animals and humans and may contaminate food. Toxoplasma oocysts shed in the feces of infected felids may contaminate food but tissue cysts in meat animals are also a source of infection, as are tachyzoites shed in milk. Echinococcus spp. eggs shed in the feces of infected canids (largely dogs and foxes) may impact food.
The BIOHAZ panel said to define targeted control strategies more knowledge needs to be acquired on the importance of foodborne transmission for each of the three parasites.
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