The larval stage of the pork tapeworm Taenia solium infects the human nervous system, causing neurocysticercosis. This disease is one of the main causes of epileptic seizures in many less developed countries and is also increasingly seen in more developed countries because of immigration from endemic areas. Little information is available on the natural evolution of taeniasis or cysticercosis. Available therapeutic measures include steroids, treatments for symptoms, surgery, and, more controversially, antiparasitic drugs to kill brain parasites. Efforts to control and eliminate this disease are underway through antiparasitic treatment of endemic populations, development of pig vaccines, and other measures. Taenia solium infection and the resulting disease neurocysticercosis are endemic in less developed countries where pigs are raised as a food source.
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Metrics details. Taenia solium , a zoonotic tapeworm, is responsible for about a third of all preventable epilepsy human cases in endemic regions. In Europe, adequate biosecurity of pig housing and meat inspection practices have decreased the incidence of T. Pigs slaughtered at home may have been raised in suboptimal biosecurity conditions and slaughtered without meat inspection.
As a result, consumption of undercooked pork from home slaughtered pigs could pose a risk for exposure to T. The aim of this study was to quantify the risk of human T. A quantitative microbial risk assessment model QMRA was developed and porcine cysticercosis prevalence data, the percentage of home slaughtered pigs, meat inspection sensitivity, the cyst distribution in pork and pork consumption in five European countries, Bulgaria, Germany, Poland, Romania and Spain, were included as variables in the model.
This was combined with literature about cooking habits to estimate the number of infected pork portions eaten per year in a country. The results of the model showed a This difference is brought about by the higher prevalence of cysticercosis in pigs that are home raised and slaughtered.
Meat inspection did not affect the higher exposure from pork that is home slaughtered. Cooking meat effectively lowered the risk of exposure to T. We propose systematic reporting of cysticercosis cases in slaughterhouses, and in addition molecularly confirming suspected cases to gain more insight into the presence of T.
Taenia solium is a zoonotic tapeworm, with pigs as intermediate hosts and humans as definitive hosts. Pigs can become infected by ingestion of T.
When eggs are ingested, oncospheres hatch from them, penetrate the intestinal walls and migrate towards the muscles. The oncospheres develop into T. Humans can become infected when pork with T. The adult tapeworm manifests in the human intestines, causing taeniosis. Human taeniosis is often undiagnosed, with mainly abdominal pain and bloating as reported symptoms [ 3 ]. Humans can obtain cysticercosis from direct contact with tapeworm carriers, contaminated food or water or through autoinfection or self-infection due to lack of sanitation [ 4 ].
Besides muscles, humane predilection sites are the eyes, subcutaneous tissues and brain. In contrast to human taeniosis, human cysticercosis may cause major health problems. Neurocysticercosis NCC is the most severe form of human cysticercosis, where cysticerci localize in the central nervous system. NCC is responsible for almost a third of all preventable epilepsy in endemic regions, mostly situated in low income countries [ 5 ].
The risk factors for human cysticercosis include poor personal hygiene, poor pig-raising practices [ 6 ], a lack of safe drinking water and sanitary latrines [ 7 ], consumption of infected, undercooked pork and poor knowledge about cysticerci in meat products [ 6 , 8 ].
These conditions prevail in low income countries where pigs are raised and consumed, i. These farms hold at least pigs and have a biosecurity that is designed to minimize the transmission of pathogens like T. As a result, every pig carcass in the slaughterhouse is checked for cysticerci. Since almost no cases are reported in Europe [ 11 ], T. Nevertheless, various recently published papers conclude differently [ 12 , 13 , 14 , 15 , 16 ]. A systematic review on the epidemiology of T.
Human cysticercosis was even reported in all countries except Iceland. Most of these patients had visited endemic countries, which might explain the acquired infection, but there are also patients that had never left their country [ 13 , 15 ]. Autochthonous cysticercosis cases could come from travellers with a taeniosis infection.
But, this does not explain the porcine cysticercosis, that is notified in Austria, Bulgaria, Germany, Poland, Romania, Serbia and Spain, all between and [ 12 , 13 , 16 ]. Apparently, the conditions necessary for the transmission of T.
Taenia solium transmission via the home slaughter of pigs was considered as a risk factor for the exposure to T. The aim of this study was to analyse the risk of T. We developed a QMRA model that followed the steps from porcine cysticercosis prevalence up until exposure of humans to infected pork portions.
First, a general model description of the steps is given in Fig. Secondly, the data sources and the calculations necessary to assess the risk of exposure per country are described in detail. The calculation steps are visualized in Fig. The model was divided in three subsections: production, inspection and consumption. All steps were made at country level. The following steps were included Fig. By taking into account the total number of portions eaten in a country in a year, the portion prevalence and total number of infected portions could be obtained.
The portions consumed well-cooked were assigned zero risk, to calculate the final portion prevalence after cooking and thus to calculate 9 The risk of exposure. This regulation lists all organs and muscles that need to be visually inspected. Regarding T. Before , the heart had to be incised lengthwise once, in order to view the ventricles and septum of the heart. As only the heart was cut to detect cysticerci, we assumed that the cut in the heart was the basis of European meat inspection for T.
To model this, the probability f to uncover a single cyst in the heart was calculated formula 1. The surface revealed by meat inspection is the area that can be inspected after the lengthwise incision mentioned above. Total slicing is the golden standard method to find T.
Organs and muscles are sliced in 0. As such, total slicing gives the largest possible area that can be checked for T. The surfaces of formula 1 are adopted from Boa et al. The probability to find at least one cyst in the heart during detection was obtained with formula 2. When the total number of cysticerci in the heart n heart increases, the detection probability follows.
The exposure of pigs to T. The probability of having an infection with n heart cysticerci was described by a Poisson distribution formula 3 , which is used for events that happen at random with a constant rate to an individual, i. A higher exposure to eggs leads to a higher probability and infection load. When the exposure rate of a country is known, the formula can be used to determine the number and load of infected pigs with cysticercosis in that country, adjusted for the meat inspection sensitivity.
Note that the exposure rate is the rate of exposure of the heart per lifetime, since this is the muscle that the prevalence is derived from. When combining formulae 2 and 3 , the following formula results:.
This probability of finding a positive pig is analogous to the reported prevalence in European countries, as the sensitivity of meat inspection and the exposure rate lead to found cases in the slaughterhouse. A binomial distribution was used to find all infected and non-infected pigs in the model, with n the number of pigs and P detect formula 4 the probability of detection.
The reported prevalences were acquired in three steps. Firstly, the number of porcine cysticercosis cases per country was adopted from two reviews about the epidemiology of T. An additional literature search was done for European countries that were lacking from the reviews [ 21 , 22 ]. Secondly, for all countries that reported an annual number of cases but no total number of tested pigs, the total number of pigs slaughtered in slaughterhouses was taken from Eurostat [ 23 ].
Thirdly, the annual number of cases was divided by the annual number of slaughtered pigs to generate a prevalence of reported cases. This is the controlled reported prevalence, because all reported cases were found in slaughterhouses [ 13 , 16 , 21 , 22 ]. The adjusted number of infected pigs originating from controlled housing was divided by the total number of pigs assessed to obtain the adjusted prevalence in a controlled setting.
Home slaughtered pigs are more likely reared in uncontrolled housing systems. This could imply that home slaughtered pigs have also had a higher exposure to T. This assumption is supported by data from Spain, where home slaughtered animals are inspected according to the same method as regularly slaughtered animals. The reported prevalence in Spanish pigs under controlled conditions ranges between 0. The ratio between controlled and home reported prevalence in Spain was used to calculate the home prevalence in other countries in our model.
Formula 6 demonstrates the step to the exposure conversion, that was applied in the model for all countries to convert the adjusted controlled prevalence in the adjusted home prevalence. The database Eurostat records the annual number of slaughtered pigs per European country, as well as the number of pigs slaughtered at places other than the slaughterhouse [ 23 , 24 ].
The yearly slaughter records taken into account are the same years for which the national number of porcine cysticercosis cases is known. The average of these years was used in the model to calculate an average prevalence.
The distribution of T. The predilection sites described are for instance the pork shoulder, pork leg and psoas muscle [ 25 ]. To take into account the cyst distribution in the model, literature data were used. In a paper of Boa et al. The average amount of cysticerci per cut was divided by the average total cysticerci of the 24 pigs.
The mean percentage of total cysticerci in the cut was divided by the mean percentage of the weight of that cut to calculate the relative cyst density [ 19 ]. The relative cyst density is the probability of a cyst being present in a cut. The relative cyst density of the heart was used in formula 5 as p heart. The weight of the pork cuts was not available from literature.
To obtain the actual cut weights in kilograms, literature about porcine brain weights of pigs in the same age class was used, since brain weight is a stable proxy for age [ 26 ]. This is shown in formula 7. The trunk muscles, musculus psoas , musculus triceps brachii , forelimb, abdominal muscles and hindlimb were not deducted from the brain weight, because those are only parts of the pork cuts loin, tenderloin, shoulder, foreleg, belly and ham, respectively.
For these cuts we assumed a homogeneous distribution within the complete cut, so that the relative cyst distribution of the muscles described in Boa et al. The weight of these cuts was collected from literature [ 27 , 28 , 29 , 30 ]. A couple of steps were followed to determine how many cysticerci end up in the consumed portions of all pork cuts.
Taenia solium Taeniasis/Cysticercosis
The cestodes Taenia saginata beef tapeworm , T. Taenia solium can also cause cysticercosis. Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata , T. Humans are the only definitive hosts for these three species. Eggs or gravid proglottids are passed with feces ; the eggs can survive for days to months in the environment.
Taeniasis/cysticercosis fact sheet
Taenia solium infection taeniasis is an intestinal infection with adult tapeworms that follows ingestion of contaminated pork. Cysticercosis is infection with larvae of T. Adult worms may cause mild gastrointestinal symptoms or passage of a motile segment in the stool. Cysticercosis is usually asymptomatic unless larvae invade the central nervous system, resulting in neurocysticercosis, which can cause seizures and various other neurologic signs. Neurocysticercosis may be recognized on brain imaging studies. Fewer than half of patients with neurocysticercosis have adult T. Adult worms can be eradicated with praziquantel.
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