**3.1 Epidemiology of** *T. solium*

Estimates are that millions of people worldwide are infected with *T. solium*, a tapeworm with more important clinical significance than the other two taenia species. In addition, infections with *T. solium* have greater importance in economically undeveloped countries with poor sanitary conditions, practices of inappropriate cooking and meat processing, extensive pig farming, and low awareness about taeniosis and cysticercosis.

Taeniosis and cysticercosis are endemic in the Andean region of South America, Brazil, Central America, and Mexico; China, the Indian subcontinent, Southeast Asia; and sub-Saharan Africa (**Figure 1**) [25]. In non-endemic countries, that is, many European countries, the USA, Canada, and Australia, reporting of HCC is due to increased consumption of pork, travel, and an increased flow of immigrants [26, 27].

Epidemiological studies estimate 2.56 million human taeniosis cases worldwide and 8.3 cases of cysticercosis [28–31], including at least 400,000 symptomatic cases in South America [32], 1.5–3 million cases in sub-Saharan Africa [29], and 3–7 million cases of HCC in China [32]. Prevalence figures vary in these countries but are usually less than 1:1000 for taeniosis, 1–10% for HCC (undifferentiated cysticercosis and neurocysticercosis), and up to 20–40% for porcine cysticercosis. Estimated seroprevalences are; for *T. solium* in Africa 17.3%, South America 13%, and Asia 15.6% [26]. Children get NCC less often than adults, probably due to a shorter exposure time and/ or a different immune response. Likewise, there is no significant differences in the prevalence of HCC between genders or different genetic predispositions in humans.

In most African countries where pigs are raised extensively, cysticercosis caused by *T. solium* is extremely widespread. In the previous decades, this zoonosis in Africa receives more attention due to the recognition of the importance of NCC in


#### **Table 1.**

*Characteristics and distribution of T. saginata, T. solium and T. asiatica.*

the etiology of epilepsy. Likewise, data from West and Central Africa suggest that human cysticercosis often does not reflect a true picture of the situation, in contrast to reported prevalences of porcine cysticercosis. Regions of hyperendemicity are in Africa [33] where a high prevalence of cysticercosis in pigs is accompanied by frequent infections with *T. solium* in humans (HCC/NCC). In West Africa, cysticercosis caused by *T. solium* in pigs and humans is reported in Benin, Zambia, Cameroon, Burkina-Faso, Ghana, Côte d'Ivoire, Senegal, and Togo. Although official data are lacking, *T. solium* is probably present in a number of other West African countries [34]. In Central African countries, pig and human cysticercosis are (hyper) endemic in Rwanda, Burundi, the Democratic Republic of Congo, Cameroon, and Chad [34]. Epidemiological studies carried out in Togo and Benin revealed that the prevalence of HCC in Togo was 2.4% and 1.3% in Benin. In some regions of Nigeria, the prevalence of porcine cysticercosis was 20.5%, while the prevalence of taeniosis 8.6%. However, it is surprising that not a single case of HCC/NCC is reported, although epilepsy is very common. Epidemiological data on HCC clearly indicate that, with the exception of predominantly Muslim countries

**Figure 1.**

*Worldwide distribution of T. solium infection in 2022 [24].*

in North Africa, cysticercosis caused by *T. solium* is endemic in all regions of Africa [35]. Thus, cysticercosis is probably one of the main causes of epilepsy in Cameroon with an incidence rate of as much as 44.6% [36, 37]. Although there is a significant association between cysticercosis and acquired epilepsy in Africa, research on this topic is lacking [35].

In Eastern and Southern African countries, *T. solium* is a serious public health and agricultural problem [38, 39]. Based on available information, annual losses due to cysticercosis in pigs in 10 West and Central African countries amount to around 25 million euros. The financial losses caused by HCC are very difficult to estimate, but they certainly exceeded burden of diseases on the animal side. Because NCC is an important cause of epilepsy, complex treatment dramatically increases the burden of the disease due to the social stigma and discrimination that accompanies the condition. The actual prevalence of cysticercosis caused by *T. solium* in pigs and humans in Central and West Africa is still underestimated due to unreliable data and lack of awareness and diagnostic capacity.

Available data from South America indicate a very significant risk of infection with *T. solium* in humans, although prevalence rates vary from country to country. For example, studies in Honduras, Peru, Mexico, and Guatemala reveal neurological symptoms of NCC in rural populations in 9–18% of residents [40]. Mexico is one of the countries with the highest prevalence of the disease, ranging from 0.2 to 3.4%. NCC in humans in Mexico has often been confirmed post-mortem as the cause of 4–13% of deaths. The reported prevalence of cysticercosis in pigs in Mexico, determined in slaughterhouses, is 0.2%, which is extremely low and does not represent a realistic estimate, as there are a large number of unconfirmed cases [40]. Data on the epidemiology of cysticercosis in most South American countries are unreliable due to a lack of official disease reporting and databases.

Fewer hospitalizations due to cysticercosis were reported in Brazil, Ecuador, and Mexico, as well as reductions in mortality rates in Brazil and in ambulatory cases care in Mexico. Data available in Ecuador compile all forms of cysticercosis, while data on HCC and NCC from Brazil and Mexico allow us to determine that NCC accounts for approximately 90% of all recorded cases of cysticercosis. Thus, the trend of confirmation of cysticercosis in pigs results in higher confirmation of NCC in humans. The trend of NCC burden in Colombia increased significantly between 2009 and 2019 [41]. Serological surveys of HCC and NCC conducted in Colombia from 2008 to 2010 showed high human exposure to *T. solium* [41].

The trend of increasing seropositivity with age is not surprising given that *T. solium* antibodies probably persist for several years. Seropositivity may be an indicator of lifetime prior exposure. In Colombia, *T. solium* antibodies were confirmed more in women than men. This data is consistent with the results of numerous other studies conducted in South America [42–45]. In contrast, in other endemic areas, such as sub-Saharan Africa, males are associated with an increased risk of exposure and higher antibody positivity [46].

Due to human migration, HCC and NCC are also reported in developed countries, such as the USA, where HCC is predominantly an imported disease with a high prevalence in immigrants [47, 48]. In Western Europe, cysticercosis was under control during the last century, but with a significant increase in connection with immigration. Imported human cases are reported from 1990 to the present in all countries except Iceland [49]. Most of the cases are confirmed in Portugal and Spain, but suspected indigenous cases are rare. Simultaneously, cases of cysticercosis in pigs are sporadically reported [50, 51]. In Eastern European countries, the prevalence of cysticercosis exceeds the occurrence in Western Europe. Cases of infection are confirmed in 15 out of 22 countries with the largest number of diagnoses in Romania and Serbia, considered as autochthonous cases [49]. In cases of taeniosis, species identification was not performed [49].

In Asia, taeniosis/cysticercosis has been occurring for several hundred years, but until recently has not received much attention. Consequently, epidemiological data for some areas of the continent do not exist. Data on taeniosis are more available than on cysticercosis [52]. Taeniosis and cysticercosis caused by *T. solium* are common in Bali and Indonesia [53]. In the serological survey in Bali, 21% of people were positive for cysticercosis [54]. Taeniosis is widespread especially among the non-Muslim population, although it is not always certain which species of Taenia is a cause. Cysticercosis is confirmed in India, especially in the north [55]. NCC is confirmed in 50% of patients with epileptic seizures in India. Infections with *T. solium* are reported in Thailand [56], South Korea [57], Taiwan [58], and Nepal [59]. In Nepal, a surprisingly high rate of taeniosis of 50% is found in areas with extensive pig farming. In China, the average prevalence of *T. solium* taeniosis in the investigated regions ranged from 0.05 to 15% [59]. In endemic areas, pig cysticercosis prevalence varied from 0.4 to 15%, and occasionally up to 40%.

#### **3.2 Epidemiology of** *T. saginata*

*T. saginata* has a global distribution; however, the taeniosis it causes is of particular importance in Africa, South America, and Asia [60, 61]. In contrast to *T. solium*, it is considered that *T. saginata* represents a less serious public health problem because this taeniosis rarely leads to serious clinical signs and symptoms in humans. *T. saginata* also leads to significant economic losses, especially in livestock production, and represents a serious problem when it comes to food safety.

#### *Epidemiology of Taeniosis/Cysticercosis in Humans and Animals DOI: http://dx.doi.org/10.5772/intechopen.110727*

Ingestion of *T. saginata* eggs cannot cause cysticercosis in humans, and the public health impact of this parasite is limited to intestinal infection (taeniosis). A risk factor for taeniosis caused by *T. saginata* in humans is the consumption of raw or undercooked beef. According to the prevalence of *T. saginata* an area can fall into one of three categories: (i) highly endemic areas with a prevalence exceeding 10%; (ii) areas with moderate prevalence; and (iii) regions with a prevalence below 0.1% or free of infection. Highly endemic areas include the Central and East African countries (Ethiopia, Kenya, and the Democratic Republic of the Congo) [62]. Endemic areas appear in the Caucasus, Turkey, Iran, Central Asian regions (**Figure 2**), and in the Mediterranean (Syria, Lebanon, and the countries of the former Yugoslavia). The prevalence of taeniosis in humans and cysticercosis in cattle is particularly high in Africa, South America, and some parts of Asia [64].

Research on the prevalence of *T. saginata* in Asia indicates the highest occurrence in the Philippines (33.7%), Pakistan (7%), Vietnam (5.8%), Indonesia (4.6%), Nepal (4.3%), and India (3.8%). In highly endemic regions, for example, Ethiopia, Bali, and Tibet, the prevalence of taeniosis is 22–27%. Cases of taeniosis are reported in Angola, Ethiopia, Kenya, Madagascar, Malawi, South Africa, Tanzania, Uganda, Zambia, and Zimbabwe. In Sichuan and Yunnan provinces of southwestern China, Bali, and Indonesia, raw beef is a delicacy. Consequently, in these rural areas, the prevalence of taeniosis in humans is higher than 20% [65].

*T. saginata* infections in North America are rare, except in cases where livestock and humans live in close proximity and where poor sanitation prevails. The prevalence of *T. saginata* (under 0.5%) is low in the USA, Canada, Australia, South America, and some countries of the western Pacific, but is slightly higher in Central America [66]. In Europe, infection with *T. saginata* is still endemic in some regions, although the prevalence is low (usually <0.05%) [61].

Taeniosis/cysticercosis caused by *T. saginata* is largely considered a neglected disease in southern and eastern Africa. The reason is low confirmation of infection in cattle, lack of data on the impact of the infection on livestock production

**Figure 2.** *Prevalence of human taeniosis in central and western Asia and the Caucasus [63].*

and economy, and viewing the disease in humans as a minor health problem. Nevertheless, the presence of cysticercosis in cattle is a clear indicator of inadequate sanitary conditions, inadequate meat inspection and human habits that may favor transmission.

The prevalence of cysticercosis in cattle relates to the prevalence of taeniosis in humans. Prevalence in cattle varies from very low (0.03%) in North America and Europe, to very high in Africa and South America (10%–80%) [61, 66]. Cattle cysticercosis in Eastern Europe is generally more frequent than in Western Europe [67]. Information on the prevalence of cysticercosis in cattle in African countries is quite limited, but a very high prevalence of up to 80% is reported (Ethiopia, Botswana, and Nigeria). In Asia, information is also scarce, in general, Japan is considered free of autochthonous bovine cysticercosis based on meat inspection results [68], very high prevalences are reported in various parts of Korea and 2.2% in Indonesia [69]. In contrast, the prevalence is very low in India [70] and the Philippines [71].

#### **3.3 Epidemiology of** *T. asiatica*

*T. asiatica* is overlooked in the context of its impact on the global distribution of taeniosis/cysticercosis in humans. We assume that there are two reasons for the above; the first is the supposedly non-cosmopolitan character of the tapeworm and the second is the close molecular similarity to *T. saginata*, suggesting that *T. asiatica* probably does not cause HCC since *T. saginata* eggs are not infectious to humans. However, *T. saginata* does not cause cysticercosis in pigs, while *T. asiatica* does.

*T. asiatica* was described in 1993 as a new species of tapeworm that infects humans [6]. Previously, its occurrence in rural communities in Southeast Asia was attributed to *T. saginata* which is morphologically very similar but described in patients who ate raw pork liver but not beef [72]. Currently, there is no specific immunodiagnostic method to confirm *T. asiatica*, and molecular techniques (the only tool for distinguishing between the 3 Taenia species) are not used in routine diagnostics. Hence, the geographic distribution of *T. asiatica* and its ability to cause HCC remain open questions. *T. asiatica* is confirmed in Asia (Korea, China, Japan, Taiwan, Indonesia, Thailand, Nepal, Vietnam, the Philippines, Cambodia, and Myanmar) [72]. In a study conducted in Thailand, all three species of Taenia appeared in communities where undercooked pork and beef were consumed, and at least one dual infection with adult tapeworms *T. solium* and *T. asiatica* was confirmed by DNA analysis. In many countries of East, Southeast, and South Asia, which are rich in cultural, ethnic, and religious diversity, all three types of Taenia coexist.
