**2. Burden of schistosomiasis in Africa**

#### **2.1 Human schistosomiasis in Africa**

The two major *Schistosoma* species infecting humans in Africa are *Schistosoma haematobium* (*S. haematobium*), which causes urogenital schistosomiasis, and *Schistosoma mansoni* (*S. mansoni*), the causative agent of intestinal schistosomiasis. *Schistosoma guineensis* (*S. guineensis*) also causes intestinal schistosomiasis but is less prevalent. In Africa, *S. mansoni* is found in all countries while *S. haematobium* is found in all but four countries (Eritrea, Burundi, Mauritius, and Rwanda). The less common *S. guineensis* (also called *Schistosoma intercalatum* (*S. intercalatum*)) has been identified in the rain forest areas of western and central Africa. Schistosomiasis transmission has been interrupted in Equatorial Guinea, Morocco, Tunisia, Algeria, Djibouti and Lesotho [2].

The number of deaths attributable to schistosomiasis is difficult to estimate because of hidden pathologies such as liver and kidney failure, bladder cancer and ectopic pregnancies; in addition, the death rate may have decreased over the past decade due to the implementation of large-scale preventive chemotherapy campaigns [3].

The most prevalent species in Africa, *S. haematobium* causes approximately 112 million cases per year. It is estimated that 71 million of these infected individuals experience hematuria (blood in the urine), half of whom have dysuria, and about 18 million suffer from urinary bladder pathology. The current best estimate is that kidney failure due to *S. haematobium* infection is responsible for about 150,000 deaths annually in Africa. More than 54 million individuals are estimated to become infected with *S. mansoni*, with around 4 million people experiencing diarrhea and 8.5 million hepatomegaly; hematemesis-associated deaths are estimated to total about 130,000 annually [2].

Chronic disability is far more common than death. Intestinal schistosomiasis can result in abdominal pain, diarrhea, and blood in the stool. Liver enlargement is common in advanced cases, and is frequently associated with an accumulation of fluid in the peritoneal cavity and hypertension of the abdominal blood vessels. In such cases, there may also be enlargement of the spleen. Hematuria is the classic sign of urogenital schistosomiasis. Fibrosis of the bladder and ureter, bladder cancer, and kidney damage are sometimes diagnosed in advanced cases. In women, urogenital schistosomiasis may present with genital lesions, vaginal bleeding, pain during sexual intercourse, and nodules in the vulva. In men, urogenital schistosomiasis can induce pathology of the seminal vesicles, prostate, and other organs. This disease can also have other long-term irreversible consequences, including infertility. In children, schistosomiasis can cause anemia, stunting and a reduced ability to learn (although the effects are usually reversible with treatment). Praziquantel is the drug of choice for the treatment of schistosomiasis. The drug is recommended for the treatment of all forms of schistosomiasis. Despite that reinfection may occur after treatment, the risk of developing the severe disease is reduced after initiation of treatment [3].

The prevalence of human schistosomiasis in Africa is estimated to be 192 million, which is 93% of the total global prevalence of the disease. About 29 million people

are infected by this disease in Nigeria, 19 million in Tanzania, and 15 million each in the Democratic Republic of Congo and Ghana, while Mozambique, with 13 million cases, completes the list of five countries with the greatest prevalence in Africa [5]. The heavy burden of schistosomiasis in Africa is attributed to limited access to clean water, poor sanitation and inadequate health services [2].

### **2.2 Animal schistosomiasis in Africa**

In Africa, animal schistosomiasis is a common parasitic infection among cattle, although it rarely infects other domestic animals such as goats and sheep; nor does it appear to trouble wild rodents and primates [6]. It is estimated that 165 million domestic cattle are affected by schistosomiasis worldwide. The disease is of veterinary and economic significance [7]. In China, 1.5 million cattle suffer from schistosomiasis, and more than 5 million are at risk of infection [8]. Schistosomiasis among livestock does not show clinical effects in most cases. However, if the infection persists for a long time, it can cause enteritis and anemia, as well as emaciation leading to significantly reduced productivity and growth, and even death [9]. Schistosomiasis in animals is caused by several *Schistosoma* species. For example, *Schistosoma japonicum* (*S. japonicum*) (which infects human beings) has been reported to infect more than forty mammal species, including wildlife such as water buffaloes, camels and rats, and domestic animals such as cattle, sheep, pigs, dogs, donkeys, cats and goats [8, 10]. *S. mansoni*, which causes human intestinal schistosomiasis, has been reported to infect at least nine other members of the Primate order, such as monkeys and apes [10]**.**

The three species with significant animal health impact in Africa are *Schistosoma bovis* (*S. bovis*)*, Schistosoma curassoni* (*S. curassoni*) and *Schistosoma mattheei* (*S. mattheei*) [2, 7]. The latter two species are known solely from domestic animals [11]. *S. mattheei* is found in southeastern Africa, from South Africa northward to Tanzania and Zambia*. S. bovis* is most common in northern Zambia and northern Senegal [12, 13]. *S. curassoni* has been found in livestock (cattle, sheep and goats) in West African countries [2]*.*

The distribution of *Schistosoma* species is governed by the intermediate host habitat—freshwater bodies such as lakes, dams and rivers. A recent study showed that *S. bovis* can cause high levels of infection among cattle in Côte d'Ivoire, where prevalence rates of up to 53.3% have been recorded [13]. Factors such as age and breed are significantly associated with different rates of schistosome infection. For example, cattle aged 4 years and above have higher rates of *S. bovis* infection than younger ones. "Zebu" and "Taurin" breeds are less likely to have *S. bovis* infections than "Taurin x Zebu" [13]. Livestock management systems in Tanzania have been shown to influence trematode distribution. The highest rates of trematode infection in cattle are found in traditional management systems in which animals are grazed and watered on communal land during the day and housed around the households in open bomas (livestock enclosures) at night. Rates of trematode infection are moderate in large-scale dairy systems and lowest in small-scale dairy systems [14].

Like a human, animals are treated for schistosomiasis through the administration of praziquantel. Effective treatment requires two rounds 3 to 5 weeks apart. However, unlike human schistosomiasis, which is frequently controlled by preventive praziquantel chemotherapy in areas where the infection is endemic [15], schistosomiasis in domestic animals is rarely treated in Africa, probably because little attention has been given by scientists to its zoonotic potential.

Schistosoma *Hybridizations and Risk of Emerging Zoonosis in Africa: Time to Think of a One… DOI: http://dx.doi.org/10.5772/intechopen.103680*
