Concordant with the distribution patterns of human schistosome species animal schistosomes are mainly restricted to the tropical and subtropical areas. Two genera of animal schistosomes of importance are listed in the literature survey. This includes species belonging to the genera Schistosoma and Orientobilharzia.
Within Schistosoma a differentiation can be made between species with and without zoonotic importance. Those of zoonotic importance are: S. japonicum (described from cattle, buffaloes, goats and pigs), S. mattheei (found in cattle and buffaloes) and S. curassoni (found in cattle, goats and sheep). The non-zoonotic species also have limited host specificity and they are listed in the database as occuring in the hosts mentioned in brackets after each species, S. bovis (cattle, sheep and goats), S. indicum (cattle, goats and sheep), S. spindale (cattle and goats), S. nasalis (cattle, buffaloes and goats) and S. incognitum (pigs).
Orientobilharzia turkestanicum was described as occuring in cattle and sheep.
The distribution patterns of the different species are presented in fig. 2. The prevalence of the species is high in the African and Asian continents.
Generally the pathogenecity of bloodfluke infections in grazing animals is considered to be low, only occasionally causing serious problems (Dunn, 1978).
AMERICA
Regions 1, 2 and 3
Apart from reference 01241 (Mexico) no observations in the data base.
AFRICA
Region 4. Northern Africa
The majority of the observations are related to S. bovis infection in sheep and cattle. The incidence in cattle are highly variable, which may reflect differences in the diagnostic methods used. In Tanzania in an abattoir survey the infection rate was estimated at 31 % (06323) and for Sudan comparable figures are mentioned (02179, 03402). An underestimation of the incidence is likely to occur when faecal analysis is used. Cattle are highly resistant to reinfections (04615, 06235) with S. bovis and F. gigantica (02179). In sheep the homologue resistance was not shown (03684). Mortalities as a result of primary infections in cattle in Sudan were described giving a mortality rate of 7 % in animals 6–30 mths old (06235). In the majority of countries in this region S. bovis has been described from cattle and sheep, in Tanzania also in goats (06323, 4 %).
Schistosoma curassoni was mentioned in Niger as occurring in cattle, goats and sheep (00589).
Region 5. Equatorial Africa
In comparison with the situation described for Region 4 the differences are mainly seen with regard to the presence of Schistosoma mattheei, described in Mozambique in cattle and buffaloes (01132, 01133).
S. Bovis infections in cattle were found in Senegal (00887, 01492), Togo (02164), Nigeria (07019), Congo (02731) and Zambia (incidence 65 %, 05972, 03827).
Extensive research in Senegal provides data concerning the prevalence of S. bovis and S. curassoni in cattle, sheep and goats. In abattoir surveys (01039, 01492, 00887, 04989) S. bovis was noticed in cattle in particular (15–62 %) whereas S. curassoni infections were abundant in small ruminants (2–16 %). Although rare, mixed infections were described in goats (03114).
Region 6. Southern Africa
In the only survey for Zimbabwe the presence of Schistosoma mattheei in cattle was mentioned (00964).
ASIA
Region 7. South Western Asia and India
Between the western part of Asia and the Indian peninsula a conciderable variation was noted in the presence of the the different bloodfluke species. In the former area infections in cattle have been exclusivily attributed to Schistosoma bovis while S. indicum, S. spindale and S. nasalis have been found in the latter. Moreover, Orientabilharzia turkestanicum infections in cattle (Iraq, 05686) and sheep (Turkey, 03745, 01268) were not described east of Iran and the occurrence of O. turkestanicum seems to be restricted (03745).
In Israel and outbreak of schistosomiasis, due to S. bovis leading to mortalities in cattle and sheep was described (07107, 02168).
In India infections with S. indicum (04008; 03514, 50%), S. spindale (04008; 02333, 80%) and S. nasalis in cattle have been described. The last species has also been found in buffaloes (03602). In Sri Lanka (07431) and Bangladesh (05643), S. nasalis infections were reported in cattle.
In goats the same species have been found in India (04008, 05981) and Bangladesh (02592, 05899). Only infections, including mortalities, caused by S. indicum are described in sheep (03534, 05981, 07323 and 03346).
In pigs in India Schistosoma incognitum infections are known to occur (00741, 80 %; 06229,04008).
Region 8. Central East Asia
The information in the database with regard to bloodflukes in this region is limited to China and Taiwan. Observations concerning Schistosoma japonicum infections have been made for cattle, buffaloes, goats (07148, 00577) and sheep (03163). Moreover, the occurrence of Orientobilharzia turkestanicum is described in cattle and sheep (03390, 03470).
Region 9. South East Asia
The information with regard to animal infections by Schistosomidae is limited to some observations in cattle and buffaloes in Thailand, Vietnam and Malaysia. S. bovis and S. nasalis have been recorded (00919, 03421, 03258). One observation on S. incognitum in pigs was described in 00732.
On The Philippines S. japonicum was found in cattle, goats and pigs (03995) and in buffaloes (03924), although at a low incidence.
Fig 2. Distribution of bloodflukes in developing countries
Three groups of Amphistomes of the gastro intestinal tract can be distinguished based of their location:
species inhabiting the duodenum as larvae, and invading the rumen at a later developmental stage. Major pathogenic effect caused by larvae in duodenum.
species living in the lower alimentary tract. These are considered to be of minor veterinary importance
species inhabiting the duodenum and bile ducts.
Apart from 13 species of Paramphistum, the following genera Cotylophoron, Carmyerius, Gastrothylax, Calicophoron, Fischoederius and Ceylonocotyle were noticed, often represented by more than one species, and included in the data base. From the lower alimentary tract, Gastrodiscus and Homalogaster infections were described, and from the third group Gigantocotyle spp.
Because of their localization in the pancreatic ducts, Eurytrema, although members of the Dicrocoeliidae, are dealt with in this chapter.
Some distribution patterns are shown in fig. 3.
AMERICA
Region 1. Central America and the Caribbean
The majority of the cited references are from the early seventies. In Mexico (05742) and Cuba (02151, 02369) infections with Paramphistomum cervi and P. microbothrium in cattle were described. Cotylophoron has been observed in cattle and sheep (03138, 02689, 02694).
Region 2. Equatorial America
Relevant references is limited to Colombia (cattle infections by C. cotylophorum, 01352), British Guiana ( ibidem, 02286) and Brasil (cattle and sheep, 03942 resp. 00396).
Moreover, Eurytrema was found in cattle (incidence 50 %, 00581, 01341) and goats (07071).
In horses Gastrodiscus infections were present (03705).
Region 3. Southern Latin America
One Paramphistomum description from cattle in Uruguay was noticed in the data base (03802).
AFRICA
Region 4. Northern Africa
In this region Paramphistome infections with species identification were described in Algeria, Ethiopia and Somalia (cattle: P. daubney, P. clavula, P. bothriophoron;01112, 06197, 05495). In Egypt, Niger and Chad non specified Paramphistomum infections were noticed in cattle and buffaloes (07135, 02425, 05920, 06305). In Ethiopia a Cotylophoron infection was detected in cattle (06197), and in Somalia a P. clavula infection was registered in goats (04254).
The information with regard to amphistome infections in Niger include the descriptions of Carmyerius infections in cattle (05920), Paramphistomum microbothrium in goats and sheep (02196) and Gastrodiscus infections in the horse in the same publication. In Chad Gastrothylax presence in cattle was described (02836).
Region 5. Equatorial Africa
Numerous publications on amphistome infections and the number of species described for this region are included in the survey. Of the Paramphistomes identified P. microbothrium infections have been described in buffaloes and sheep in Senegal (04489), in sheep in Nigeria (02257) and in cattle in the Central African Republic (02703). Other Paramphistomum infections with species identification are P. togolense in sheep in Togo (06263) and P. cervi in cattle in Nigeria (02749).
Unspecified Paramphistomum infections in cattle, buffaloes, goats and sheep have been described from many parts of the region (Cote d' Ivoire (00680), Congo (01462) and Madagascar (02603)). High prevalence figures was registered for cattle in Uganda (06006, 03033) and Kenya (12–100%, 00536). This publication also describes a negative correlation between Paramphistomum and Fasciola infections. In Mozambique a prevalence of 22 % is described in goats (01168).
Carmyerius infections in cattle are known from Senegal, Congo and the C.A.R. (00887, 02731 and 02703).
The last mentioned reference by Graber, added Calicophoron spec., Gigantocotyle synaei and Cotylophoron cotylophoroidesto to the list of amphistomes in cattle in C.A.B. The last of these species is also known in cattle in Senegal (00887).
Region 6. Southern Africa
The information is restricted to Zambia. An incidence of P. cervi of 2 % in goats is described (03098) as is the presence of P. microbothrium in sheep (05931).
ASIA
The information from this continent is considerable, both in terms of publications and in the number of parasite species. The majority of the publications relate to the Indian peninsula; but the information concerning South Eastern Asia is extensive as well. Many publications refer to very high prevalence figures.
Region 7. South Western Asia and India
In western Asia infections with Paramphistomum daubney have been described in cattle sheep and goats. Incidence figures in cattle in Turkey are 20–25 % (03294, 00742), in small ruminants these figures are lower (00742). From Iraq and Iran the occurrence of P. cervi in cattle has been described (08858, 03928). In the latter publication by Sey the cattle list is extended with P. microbothrium, P. gotoi, Calicophoron papillosum and Gigantocotyle explanatum.
In Pakistan the prevalence of P. cervi is high in cattle (40 %, 03373, 03159) and in sheep (36 %, 04030). In sheep the incidence of Cotylophoron cotylophorum was estimated at 22 % (04030), and the combined prevalence of this species with Gastrothylax crumenifer was 15 % in goats (04003).
In India 10 species of Paramphistomumidae, inclusive Velasquezotrema tripurensis n.sp. have been described in cattle (01108).
With regard to prevalence figures Gigantocotyle explanatum (5.5 %, 07027) and the occurrence of Gastrothylax indicum (06325) they are described in cattle. In buffaloes Gigantocotyle incidence has been recorded at 91 % (07027, 03812) and 70 % (03169). In the same survey Gastrothylax prevalence was 50 %.
In goats G. explanatum incidence is low (0–2 %, 07027,01285). Mortalities due to P. cervi have been described in goats (06326), and Homalogaster infections in the same host show an incidence of 5 % (00648). In an abattoir survey combining sheep and goats intestines a wide spectrum of Amphistome genera and species is described, including P. cervi (07205) In the same publication a prevalence of paramphistomes in sheep of 40 % is mentioned.
In horses the only information with regard to amphistome infections is in reference 00699.
The literature from Bangladesh, Sikkim and Nepal (04575,00756; 08382,00809; 03059,05622,00294) accentuates the prevalence of this parasite group in cattle, buffaloes, goats and sheep in the region.
Region 8. Central East Asia
From this region information is limited to P. gracile infections in cattle and P. gotoi and Carmyerius infections in sheep in Mongolia (06205). In China 5 species of Eurytrema have been recorded in cattle, goats and sheep (07245,08877; 05591, 05593 and 08877,05593 resp.). E. pancreaticum was not observed in goats in this survey (03236).
In Korea and Taiwan non specified paramphistomes are described in cattle (00841, 05698), and the presence of G. explanatum (01028) and Eurytrema pancreaticum is mentioned as well (04455, 08841). Contrary to China Eurytrema pancreaticum was observed in goats in Taiwan (08841,05697).
Region 9. South East Asia
Although the publications from this region are limited in number, the available information suggests that the rumen and gastrointestinal fluke fauna is intermediate between regions 7 and 8. Specified descriptions of Homalogaster (08333), Fischoederius (06228), Cotylophoron (02391) and Ceylonocotyle (07953) in cattle and buffaloes are presented and Eurytrema pancreaticum infections in cattle (03281,06213, 05511) and sheep in Malaysia (07014) are known to occur.
Fig 3. Distribution of Rumen and Gastro-intestinal flukes in developing countries
This review on the geographical distribution of Fasciola and Dicrocoelium species and their host preferences is based on the selection of relevant data from literature published during the last 15 years. This has created a database which compile the most recent information on the distribution patterns of Fasciola gigantica, F. hepatica, Dicrocoelium dendriticum, D. hospes and D. chinensis.
The geographical distribution of trematode species is mainly determined by the distribution patterns of the snail intermediate hosts. Boray (1985, 1991); Over (1982); Taylor (1960).
As can be seen from the database a conciderable amount of knowledge has been accumolated on liver fluke infections in livestock reflecting the concern and interest for these infections to veterinary services and parasitologists in many countries. The reasons for this could be that it is relatively easy to make a differential diagnosis of these infec-tions at slaughter, combined with the knowledge that livers have an economic value.
Based on the accumolated material it is justifiable to consider liverfluke infections as an important regional threat to animal production in many developing countries. The infections should be controlled in herd health programs. In the absence of statistically sound epidemiological data, control programmes based on common sense, field observations and liver condemnation statistics may prove useful in the initial stages of control implementation.
3.1 AMERICA
The only liverfluke species present on this continent is F. hepatica. The differences between countries in the presence of different intermediate host species have been described (Boray 1985, 1991 and Over 1882)
Region 1. Central America and the Caribbean
Known host species are bovine animals, goats, sheep, horses and pigs. In Costa Rica and on Jamaica endemic human infections have been described ( 03406, 04790 and 01646)1.
In Mexico different prevalence data with regard to cattle have been described depending on the area (4–6 %, 00512; 74 % 06294), and a comparable variance is seen for Cuba (4–43 %, 02174). In Costa Rica prevalences based on faecal examinations have been estimated to 23– 69 % (03406) while a study on Jamaica only recorded 6 % (03403).
The infection in goats, sheep and pigs is confirmed from
several countries but the incidence was not described in any
of the references included in the database. From
slaughterhouse surveys in Mexico the prevalence in horses and
donkeys was estimated at 0.22 and 5.8% resp. (01417)
In Mexico the calculated losses from fascioliasis in Tabasco
State amounted to $ 56 million in 1979.
Region 2. Equatorial America
Within this region major problems with regard to fascioliasis were noticed in the southern part of Brasil and in the Andes area. In Brasil the incidence which has been established through faecal examinations range between 61 % in adult cattle and 50 % in calves in the Parana district (03669) and the country average based on slaughterhouse data is 12% (05861). In Rio Grande del Sol an average incidence of 15 % has been observed (05852).
In Colombia (04288) and in the Altoplano Region of Bolivia the prevalence of F. hepatica in cattle determined on faecal analysis is estimated to range between 40 and 49 %. Infected cows are less fertile and suffer a high abortion rate (04288).
In Venezuela infections are important in the mountainous areas. The number of sheep infected in the Andes sheep is very high (80 %) and it is estimated that the annual mortality of the flocks is in the order of 15–25 % (02745). The incidence in sheep is also available for Rio Grande del Sol, Brasil (7 %; 03740). The incidence in alpacas is considerable (59 %). Data with regard to the incidence are lacking for goats, horses and pigs.
Human cases have been noticed in Peru (01960).
Region 3. Southern Latin America
The most relevant information has been published from Chile. According to slaughterhouse surveys the prevalence in cattle ranges between 13 % (05817) and 94 % (07160).
From Paraguay and Uruguay incidence data for fascioliasis are not available and in Argentina mostly light infections occur in the north-western part of the country. Here liver condemnation data are estimated at 9–13 % (05625, 03796).
In Chile prevalences in horses and asses at the slaughterhouses are 5% and 28 % respectively (03563) and there is interesting observations on race horses where the infection rate was approximately 12% based on faecal examination (03150). Data on pigs show a prevalence of 1.5 and 2 % (04517, 02205).
In Argentinian sheep mortalities due to black disease caused by a combination of F. hepatica/Clostridium novyi type B infection have been described (04120).
One human case of fascioliasis was recorded from this region (00949).
3.2 AFRICA
Within this continent the description of the regional distribution of liverflukes is complicated by the separate and simultaneous occurrence of F. hepatica and F. gigantica. Moreover, on the base of morphology intermediate forms have been described in region 4 particularly.
For Dicrocoelium a similar problem exists, with regard to the differentiaion between D. dendriticum and D. hospes. Although for Algeria it has been postulated that D. hospes might be a variant of D. dendriticum (01210), they are treated here as separate species.
Region 4. Northern Africa
In Egypt by means of slaughterhouse surveys the prevalence of Fasciola infections has been estimated at 2 % in cattle, 14 % in buffaloes, 0.6 % in sheep and 8 % in pigs. Camels were not infected (03441). The distinction between the Fasciola species was not completely clear in this publication.
Based on an abattoir survey in Mali, the F. gigantica infection rate have been estimated at 50 % for Zeboes from the Sahel-area and 7% and 12% respectively for animals from the sub-desert - and the Sudanese region (01023).
In Kenya meat inspection surveys have estimated the incidence in cattle in the coastal region at 0 to 8 % and in the Nyanza region at 16–43 % (03164).
In Ethiopia fascioliasis in cattle is considered to be of great economic importance (01014). Both fasciola species occur in Ethiopia.
The incidence of D. hospes in Mali was estimated at 0–18 % in cattle from the Senegal region (04635), and the prevalence in N'Dama/Zebu crosses from the Sudanese region was recorded at 74% (01023).
Major economic losses due to fascioliasis have been described in sheep and goats in Mali when animals are grazing in irrigated systems (00966), and the same holds for Ethiopia where 45.6 % of deaths in six flocks of sheep was due to F. hepatica infections (00943).
Complications as a result of black disease in sheep have been described from Mali (03119).
In Kenya slaughterhouse prevalence figures for sheep and goats were low ranging from 2.3% to 4.4 (07134, 01119). Camels and pigs were negative.
Region 5. Equatorial Africa
Within this region the occurrence of F. gigantica and D. hospes has been described. The first species is distributed widely and Dicrocoelium is particularly known from the West African countries.
The majority of prevalence data are based on abattoir surveys. The incidence of F. gigantica in cattle is more than 50% in Senegals most affected areas near Casamanca and in the River Delta Region (03255), In Nigeria it is recorded at 60 %, (03643) and 72 % (03716). In Tanzania an incidence of 7.7 % has been published (06323). In Sierra Leone (03400) and Zaire (01350) prevalence figures are intermediate between Nigeria and Tanzania.
In the case of cattle total losses for Nigeria have been calculated at 32.5 million Pounds (03716), however a substantially lower estimate is presented in 04483 Losses in cattle are the result of totally and/or partially condemned livers (eg. 5% totally and 67 % partially, 03716), While in sheep the majority of livers are totally condemned (55 %, 00898).
Prevalence data in Madagascar based on faecal analysis in Zebu cattle show an incidence between 0 and 77 % (07177) and in Uganda with the same technique the rate is 20% (03033).
Slaughterhouse surveys for Dicrocoelium hospes infections in cattle have shown prevalences ranging from 23 to 62% in Senegal (03255, 03400), and from 17 to 56% in Nigeria (07176, 07821). According to the last reference the incidences in sheep and goats are lower (13.1 and 5.2% respectively).
Region 6. Southern Africa
Information on the prevalence of F. gigantica is limited. In Zambia important regional differences with regard to the infection in cattle (16–61 %) have been described following slaughterhouse surveys (07433). In Zimbabwe the quoted incidence figure is 6.5 % (00858).
3.3 ASIA
With regard to fascioliasis the remarks on the specificity of F. hepatica and F. gigantica made earlier for Africa are also applicable to the Asian situation. Along the northern frontiers of this region and in the higher mountainous areas both species overlap in their distribution patterns. On morphological grounds intermediate forms can be distinguished.
The situation concerning Dicrocoelium is not clear either. In China D. Chinensis has been described as different from D. dendriticum and D. hospes.
Region 7. South Western Asia and India
Information about infections of cattle, buffaloes, sheep and goats with F. hepatica are limited to Turkey (03294, 01058, 00661, 00662, 03965), Iraq, Saudi-Arabia (06312), Pakistan (03536) and Bangladesh (01198). Liver condemnation figures are generally low, the highest rates recorded for cattle being in Turkey at 29.3% and 20.3%.
The prevalence based on faecal analysis of sheep in Yemen was found to be 53% (07129) and 58% in sheep and goats in Pakistan in the Faisalabad area (03536). Moreover, in Bangladesh fatal black disease in cattle has been described (01198).
Saudi-Arabia has been identified as a transition zone between the distribution patterns of F. hepatica and F. gigantica. For the first species prevalences are 1.2, 0.04 and 0 % in cattle, sheep/goats and camels respectively. For F. gigantica the corresponding infection rates were 20, 2.4 and 10.4 % (06312).
F. gigantica infections in cattle are present in Turkey though at a low incidence 0.8 % and mixed with F. hepatica (03294). In Iraq prevalences are at the following levels, 4.8 % in buffaloes, 3.3–11 % in cattle, 0.7–9 % in sheep and 0.1–2.2 % in goats (01726, 00801, 03613). From Iran and Afghanistan no figures are available. In Pakistan in the Delta of Sind Province the F. gigantica prevalence in ruminants exceeds 50 % (03539). On the Indian Penisula liver inspection data show a high variance in prevalence depending upon local moisture conditions (07045). As a rule both according to faecal examinations and as a result of abattoir data infection rates in buffaloes exceed those in cattle (50 vs 64 %, 00472;3.7 vs 7.8 %, 03166). In buffaloes prevalence increases with age (01248).
Based on faecal analysis prevalences in cattle and goats in Sikkim are 83 and 81% respectively (03709). Mortalities have been described in buffaloes on the Nicobar Isles with erratic F. gigantica in lungs and spleens (07207). In Kashmir prevalences are high running at 85.1 % in cattle, 51.3 % in sheep and 14.8 % in goats. In this province sheep were infected with F. hepatica as well (00497).
Human cases of F. hepatica infections have been described in Yemen (01982) and Iran (09042).
Dicrocoelium dendriticum infections were noticed in Turkey in sheep, buffaloes and cattle (37 %,03294; 41 %,01058) and in goats (50 %, 00661). Mortalities in sheep with helminth numbers in excess of 15.000 were observed (01006).
In Iraq and Pakistan Dicrocoelium prevalence is low (00801, 03616, 04030) but in India faecal analysis showed infection percentages of 20, 20, 14 and 0 in cattle, buffaloes, sheep and goats respectively (00472).
In Iran human infection with D. dendriticum was described (09042).
Region 8. Central East Asia
Prevalence figures are only available from China and Korea. In South Fukien faecal analysis showed that 81 % of cattle were infected with F. gigantica, 10 % with F. hepatica and 9 % with both species. Incidence increased with age (02736).
In an abattoir survey F. hepatica infections were noticed in 60 % of cattle and 32 % of goats (04282). The infection rate was higher in buffaloes than in cattle (35 vs. 26 % according to faecal analysis).
In south Korea the prevalence of fascioliasis at the slaughterhouse and intradermal serological tests in 300.000 “healthy” cattle showed an infection rate of 36.5 % (03552). The average condemnation percentage due to F. hepatica in another survey was 45 % (03722), and it was demonstrated that out of 80 distinguished areas only 8 were completely free from infection. Other intradermal test surveys were positive in 31 % out of 53.000 resp. 30 % out of 170.000 cattle (03590, 03690).
Average loss of liver tissue per infected animal was 2.73 kg.
According to abattoir surveys the prevalence of Dicrocoelium chinensis ranged between 30–100 % in sheep and 35 % in cattle (03460, 04248).
Region 9. South East Asia
With the exception of the Philippines and Papua Nw-Guinea only F. gigantica is described for animals of this Region. F. hepatica infections are known to occur in the two countries.
In Thailand the average prevalence of F. gigantica in cattle is 16 % and in buffaloes 25 % (00569). In north-eastern Thailand the incidence increases to 75 % (07046).
In Malaysia prevalence is lower both in cattle and in buffaloes (5%, 13% and 5.2 %) as the condemnation figures in 00012, 0.4210 and 03305 show.
In the Philippines F. gigantica exceeds F. hepatica in prevalence. In cattle figures were 3 resp. 0.6 %, in buffaloes 33 vs. 7 % (03744). An average prevalence of 18 % fascioliasis affected cattle and 59 % in carabaos (00170) accentuates the differences between hosts mentioned before.
In Indonesia, however, the incidence of F. gigantica in cattle seems to be higher compared to buffaloes. In a survey depending on coprological analysis 20 % of cattle as opposed to 14 % of buffaloes were found to be positive (07123) and in an abattoir survey the figures were 61 % and 31 % respectively. In the same publication (01251) it was recorded that 22 % of sheep and 21 % of goats were infected. These high prevalence rates have been used to calculate the economic losses due to fascioliasis in cattle and buffaloes in Indonesia, and it is estimated that the infections result in a financial loss of $ 32 million., and equivalent to 28 % of the total losses in this husbandry sector (01103). However, it has been postulated that on West-Java, fascioliasis, in combination with other helminth diseases are of minor importance compared with mastitis (01024).
4. SUMMARY AND CONCLUSIONS
The impact of Fasciola and Dicrocoelium infections on the productivity of animals is to a high degree dose dependent. The number of infective metacercariae picked up by the grazing animal depend upon a number of parameters that are closely linked to the environment of the potential host. Pasture type, management procedures and regional social and environmental patterns are just a few of these factors influencing the quantity of infective larvae ingested.
Nevertheless, the result of a massive infection is predictably negative and control measures should be introduced immediately. As this review has clearly indicated the amount of information on the prevalence of liverfluke infections and the general pattern of regional epidemiology is complete enough to make a consistent approach.
Fig. 4 Distribution of Fasciola spp. in developing countries
Fig. 5 Distribution of Dicrocoelium spp. in developing countries
Only four references are listed in Annex X, ASIAMT. All the references are from Asia. Three emphasize infections of pigs with the human fluke Opisthorchis sinensis (03868, 02851) in China and Taiwan. O. noverca was described as responsible for infections in pigs in India (06159). The reference 02801 dealing with Gigantocotyle siamense infection in Afghanese buffaloes is mistakenly listed here but should have been considered in 3.2.
