Review on Bovine Schistosomiasis and its Current Status and Public Health Importance in Ethiopia

Seminar Paper, 2020

30 Pages, Grade: 18








2.1 Etiology
2.1.1 Morphology of Schistosoma
2.1.2 Taxonomy
2.2 Epidemiology
2.2.1. Risk factors for infection
2.2.2 Transmission
2.3 Pathogenesis
2.4 Life Cycle
2.5 Clinical findings
2.6 Diagnosis
2.7 Managements Of The Disease
2.7.1 Treatment
2.7.2 Control and prevention


4.1 Economic Importance
4.2. Public Health Importance




Table 1.Definitive hosts, predilection site and geographic distribution of schistsoma species

Table 2.Prevalence of Bovine schistosomiasis in different areas of Ethiopia


Figure 1.Mature schistosome worm: female lying in the gynaecophoric canal of male

Figure 2. Life cycle of Schistosomes


Abbildung in dieser Leseprobe nicht enthalten


Schistosomiasis is a parasitic disease transmitted by snail intermediate hosts. It is one of the most wide spread zoonotic disease which is endemic in many developing countries of the tropics and sub tropics causing considerable loss in humans and animals. The disease affects rural communities particularly those who depend upon irrigation to support their agriculture. Currently it affects between 200 and 300 million people in around 74 countries. The great majority (80-85%) of schistosomiasis is found in sub-Saharan Africa. Schistosomiasis is caused by trematode worms of the genus Schistsoma that live in the alimentary tract, bladder, as well as hepatic and nasal veins of humans and animals.

Effective transmission of schistosomiasis occurs when the schistosome parasites, the aquatic snail hosts and the human or animal definitive hosts meet in space and time in surface water. The pathological changes with the disease are attributed by the adult parasite, cercaria and the eggs of the parasite. Health education, chemotherapy, environmental and biological control as well as provision of clean water have an innumerable role in the control activity of the disease. The use of traditional medicines in the treatment of schistosomiasis are economically important and a growing concern.

There are various types of plants having anti schistosomal and molluscicidal properties with minimal side effects used by developing countries and continuous to be used in the modern world. Phytoplacca dodecandora (Endod) is the most widely studied molluscicide in Ethiopia.

Key words: Endod, Medicinal Plants,Molluscicide, Schistosomiasis


Schistosomiasis or bilharizia is one of the snail borne trematode infection of animals and humans caused by genus schistosoma and occurring in different parts of tropical and sub tropical countries. Unlike other trematodes, the schistosomes are dioecious , i.e.,the sexes are separated. The male surrounds the female and encloses her with in his gynacophoric canal for the entire adult lives of the worms. (Samuel et al, 2016). Schistosomiasis is a common parasitic infection of cattle mainly, in Africa and Asia, in which about 530 million heads of cattle live in areas endemic for cattle schistosomiasis and it has been reported that 165 million cattle becomes infected with Schistosomiasis all world wide. The passive immunity of the calves which they received by the colostrum in the prenatal and postnatal period reacts for the infection which they receive in the early age through water contact (Gabriel et al , 2002).

Ethiopia is highly endemic for Schistosomiasis, since temperature in Ethiopia appears to be the major factor that affects the distribution of Schistosoma species (WHO, 2010). Out of 10 species reported to naturally infected cattle, six have received particular attention mainly because of their recognized veterinary significance. The major species that cause animal schistosomiasis include: Schistosoma bovis, S. indicum, S. japonicum, S. matthei, S. intercalatum, S. nasale and S.rodhoni (Jejaw et al., 2015). S . bovis, S. matthei and S.intercalatum are the most important species that can cause schistosomiasis in ruminants.

The geographical distribution of bovine schistosomiasis has been determined primarily by the distribution of snail intermediate host particularly Bulinus species which are important for the occurrence of disease in bovine species. Schistosoma bovis is a species' whose final hosts are bovines, ovines, caprines and whose secondary hosts are small wild ruminants.

They are distributed through out Africa, South West Asia and Mediterranean, Europe (Urquhart et al., 2003).

The increasing use of irrigation in agriculture and fish breeding facilitate to increase number of snails which carry Schistosoma and as a consequence the human and animal incidence of schistosomiasis is increases. More over, level of infection, the frequency of water contacts and increasing cattle mobility through trading or rental increased the possibility of spreading the disease or infection sources (Islam et al., 2011).

In human the disease is common in about 74 developing countries and mainly affects people living in rural agricultural and peri-urban areas (Oliveira, 2004). The principal clinical signs in the affected host are mainly associated with passage of the spindle eggs through the tissue of the gut lumen. The young parasites cause some damage during migration, but most of the lesions are due to the irritation produced by the eggs of the parasites in the intestine and other organs(Marquardt and Greive, 2000; Bowman et al., 2003).

Diagnosis is primarily based on the clinico-pathological picture, seasonal occurrence, and previous history of schistosomiasis in the area or the identification of snail habitats with a history of access to natural water bodies. Praziquantel is highly effective for the treatment of bovine schistosomiasis. The goal of treatment is reduction of egg production via reduction of worm load: this reduces mortality and morbidity (Richer, 2003).

The most effective way to control cattle schistosomiasis in endemic areas is to prevent contact between the animals and the parasite. But this is not always practical in some parts of the world where nomadic conditions of management prevail, so that destruction of the snail intermediate host population at transmission sites, either by chemical or biological methods, or their removal by mechanical barriers or snail traps are some methods used as a control of the disease (Bont, 1995).

The objectives of this seminar paper is listed by the following way

- To review bovine schistosomiasis .
- To rechake the current status and public health siginifficance of bovine schistosomiasis in Ethiopia.


2.1 Etiology

Schistosomiasis are caused by genus schistosoma.There are many species under the genus Schistosoma. However, the most important species both in human and veterinary field that causes pathological changes in their associated organs or predilection sites are S. nasale, S. bovis, S. indicum, S. spindale, S. hematobium, S. intercalatum, S. japonicum and S. mattheei (Mandal, 2006).

2.1.1 Morphology of Schistosoma

Adult schistosomes have a basic bilateral symmetry, oral and ventral suckers, a body covering of asyncytial tegument, a blind-ending digestive system consisting of mouth, esophagus and bifurcated tail Schistosomes exhibit sexual dimorphism and have distinct separate sexes. Adult worms are about 0.3-3 cm in length that lives in the blood vessels around the intestine, hepatic, nasal or bladder veins. The mature male worm is broad and flat, in wardly curved forming a groove called gynaecophoric canal to clap the female which is longer than the male (Lefevre ,et al 2010). The female worm after copulation is set free to lay its eggs. Each mature female produces about two hundred ova per day.

Abbildung in dieser Leseprobe nicht enthalten

Figure 1: Mature schistosome worm: female lying in the gynaecophoric canal of male.

Source: springer 2001

2.1.2 Taxonomy

The taxonomic classification of the organism is presented as kingdom Animalia, Phylum Platyhelminthes, class Trematoda, sub class digenea,Family Schistosomatidae, Genus Schistosoma and species Schistosoma bovis, Schistosoma leiperi, Schistosoma mattheei, Schistosoma mansoni, Schistosoma hematobium, Schistosoma nasalis, Schistosoma japonicum, Schistosoma spindale, Schistosoma indicum and Schistosoma Intercalatum (Dwight et al, 2003).Schistosomiasis is a chronic debilitating parasitic disease of both human and animals, and is caused by different species of the genus Schistosoma (Pari-jia, 2004). Generally the eggs have typical morphological features. Relatively larger, slender (spindle) shaped and have lateral of terminal spine (pointed at both ends) (Urquhart et al., 2003).

2.2 Epidemiology

High rain fall is good predisposing factor for the occurrence of the parasite(Mandal, 2006). Particularly it is common in tropical and subtropical countries like Africa, Caribbean, Southeastern America, East Asia and in the Middle East. The disease affects between 200and300 million people in around 74countries. Over 600 million people are reported to be at risk of this trematode disease (Ibrahim , 2009).

The great majority (80-85%) of schistosomiasis is found in sub-Saharan Africa, due to low socioeconomy or favorable climate for breeding of the snail and transmission of the disease (Liang, et al, 2007). In Ethiopia, various epidemiological studies conducted on cattle schistosomiasis were indicative of the epidemicity of the disease in large stagnant water bodies and marshy free grazing areas. The prevalence of S. bovis has reported from different regions of the country by fecal examination (Mersha ,et al,2012). About 29.89 million people are at risk of acquiring schistosomiasis and of these 4 million are infected. The incidence in Ethiopia is increased by construction of dams, expansion of irrigation based agriculture schemes and population movements.

The intermediate hosts having veterinary and public health importance belong to the genus Biomphalaria, Bulinus, Oncomelania , Indoplanorbis, Planorbis , Radix and there are about 350 species. Most of these snails are aquatic that live under the water and can not usually survive elsewhere. But there are also amphibious snails adapted for living in and out of water (Oncomelania). A large population of snails are live in fresh waters, where the larvae of genus Biomphalaria serve as intermediate hosts of parasitic trematodes also pass part of their life (Singh ,et al 2000).

Snail of the S.mansoni in Africa and America and Bulinus serve as the intermediate hosts of S. haematobium in Africa and the intermediate hosts of S.haematobium in Africa and the Oncomelania and Tricula serve as the intermediate hosts of S.japonicum and S.mekongi, respectively. Cattle, sheep, goat zebra, horse, pig, dog, donkey man, and birds are meracida recovery through culturing (Laikemariam, et al, 2005). In areas endemic for Schistosoma, detection of spindle shaped eggs having lateral or terminal spine depending on the the gold standard technique of Schistosomiasis diagnosis (Kassi, , 1999).

It is almost similar to fasciola gigantica and paramphistomes. Schistosoma required water for hatching of the eggs. Eggs can hatch in slightly acidic ph. Sheding of cercariae is temperature dependent. Long time is required for development of shcistosoma in snail high rainfall is good predisposing factor for occurrence of these parasites (Mandal, 2012)

Epidemiological studies on bovine schistosomiasis are suggestive of the endemicity of the disease particularly in areas with large permanent water bodies and marshy pasture areas. In Ethiopia, the optimum range for distribution of S.mansoni has been reported as 1500 to 2000 meter above sea level (masl) (Gashaw, 2010).Geographic distribution, natural hosts and anatomical site of Schistosoma species were illustrated in table 1

Table1.Definitive hosts, predilection site and geographic distribution of s. species.

Abbildung in dieser Leseprobe nicht enthalten

Sourc e: Jones et al. (1983)2.

2.2.1. Risk factors for infection Host related risk factors


This might be occured due to a long exposure time because older animals move long distances in search of scarce pastures and water thereby increasing their chances of infection as well as becoming infected at overcrowded watering holes. On the other hand, the very young calf do not graze extensively as the older, so they get less infection chance of cercariae unlike adult animals. Kassaw (2007) and (Nagi et al., 1999) also reported that the increased contact time with schistosoma infested habitat increases the rate and endemicity of schistosomiasis. Infection rate increased with the increase of age and peak infection occurred at the maturity of age (Bedarkar et al., 2000).


Differences in susceptibility to infection between sexes have been observed by various workers. The observed disparity may not solely due to difference in susceptibility but may also depend on a sex-related variation in behavior that results in differences in exposure (Magona and Musisi, 2002).

The reason seems to be related to social practice of keeping females under better management and feeding condition for milk production and Males are also fed relatively poor diet which increases the susceptibility to parasitic infection (Houdijk and Athana, 2003).


According to the (Alemseged et al. 2010) reportes the local breeds are more affected by schistosomiasis than cross breeds. This difference in prevalence of the disease does not appear to be due to the difference in susceptibility but due to the difference in exposure. Cross breeds are mostly kept for dairy or fattening purpose and they are mostly housed and supplementing good feed and clean water which reduce their access to the cercariae.

However, the local once are mostly managed extensively to graze freely and get access to infective stage of the parasite.


Cattle residing in endemic areas show a typical pattern in faecal egg counts. The faecal egg excretion usually starts between 4 and 8 months of life, counts increase rapidly to reach a maximum around the age of 6–15 months and then decrease markedly by the age of 18 months (De Bont and Vercruysse, 1997). In older animals, faecal egg counts remain low, tissue egg counts seem to follow the pattern of the faecal egg counts, while worm burden tends to increase with the age of the host (vercruysse& Gabriel, 2005).

The suppression in egg production is probably induced by serum-born factors, since adult worms from cattle with naturally acquired immunity to S. bovi s, surgically transplanted into non-immune animals, produced large number of eggs again (Bushura et al., 1982, Bushura et al., 1994). Reductions in worm burden and egg counts could also be induced in non-immune calves, which received serum from immune donors (Bushura et al., 1994).

A few studies reported on heterologous resistance. Calves previously exposed to infection with the human schistosomes S. mansoni and S. haematobium were partially protected against S. mattheei and S. bovis, and it was believed that this type of heterologous resistance might be of considerable importance in protecting cattle from the more serious effects of schistosomiasis (De Bont and Vercruysse, 1997). Seasonal risk factor

Schistosome infection rate in cattle increases during rainy season. The highest infection rate in rainy season could be due to abundance of snails and their rapid multiplication and dispersion.

Furthermore, dispersion of fecal matter occurs due to rain splashes. These factors may enhance the infection of snails by miracidia and cercarial contamination to adjacent areas through water. During this time conditions on the lands are suitable for the survival of the intermediate hosts and they become heavily infected with the schistosome larval stages. So, cattle are prone to get the infection of schistosomes (Soulsby, 1982). But in dry season infection rate of the schistosome parasite is low because of harsh dry conditions and less chances of infection due to unavailability of snail intermediate hosts as the water sources are scarce in this season (Kahn, 2011).


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Review on Bovine Schistosomiasis and its Current Status and Public Health Importance in Ethiopia
public health
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Endod, Medicinal Plants, Molluscicide, Schistosomiasis
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Gizaw Mekonnen (Author), 2020, Review on Bovine Schistosomiasis and its Current Status and Public Health Importance in Ethiopia, Munich, GRIN Verlag,


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