THE POSSIBLE SNAIL INTERMEDIATE HOSTS OF DICROCOELIUM HOSPES IN NIGERIA

Fashuyi S. A., G. O. Adeoye: The Possible Snail Intermediate Hosts of Dicrocoelium hospes in Nigeria. Acta vet. Brno, 55, 1986: 85 -88. Limicolaria /lammea. L. striatula and Lamellaxis gracilis were experimentally infected with larval stages of Dicrocoelium hospes after exposure to embryonated eggs. Limicolaria proved to be more suitable, showing higher infection rates, more mature cercariae and retaining infections longer. The potential for Lamellaxis as a natural host seems higher because it is known to occur in both rain forest and drier savanna grassland where most cattle are pastured. Limicolaria is essentially a rain forest snail. Laboratory infection. cercariae. larvae. sporocysts. trematodes. There are records of Dicrocoelium hospes infections in cattle in Nigeria !1nd several other countries. Such reports include those of Graber and Oumatie (1964), Odei (1966), Williams (1969), Mahlau (1970), Kajubiri et al. (1977) and Obiamiwe (1977). Studies of its life cycle including the molluscan hosts are very sketchy and speculative in most cases. This situation contrasts sharply with Dicrocoelium dendriticum. a closely related species where almost thirty snail species and several arthropods were listed by Soulsby (1965) as intermediate hosts in Europe, America, Asia and North Mrica. Limicolaria and Achatina were suggested as possible snail hosts of D. hospes in Ghana (Odei 1966) while Bourgat et al. (1975) found larval stages of the trematode from Limicolaria/lammea. L. striatula and L. aurora collected from grazing fields in Togo. In Sierra Leone, however, Asanji (1976) failed to infect experimentally any of these snails, although the country shares similar geographical and ecological features with Ghana and Togo. It is therefore important to establish the hosts of the fluke in Nigeria for a good understanding of its epizootiology. Materials and Methods Eggs of D. hospes were recovered from the gall bladders of infected cattle or teased out of the uterus of adult worms. They were incubated to full embryonation using the method of Fashuyi (1984). Samples of Limicolaria /lammea. L. striatula. an unidentified Limicolaria sp. and young Achatina sp. were collected from the Biological Garden of the University of Lagos while colonies of Lamellaxis gracilis were raised in the laboratory. Adult Achatina sp. was purchased from open markets in Lagos. Several snails from each sample collected from the Biological Garden were dissected and examined for trematode infection. Exposure of snails to infection was carried out by isolating them in groups of five in plastic cans containing food mixed with over one hundred fully embryonated eggs for 48 hours on each occasion. Seven days after exposure, 1 2 snails of each type were dissected daily and examined * Present address: Department of Biological Sciences Federal University of Technology Akure, Ondo State, Nigeria .1

There are records of Dicrocoelium hospes infections in cattle in Nigeria !1nd several other countries.Such reports include those of Graber and Oumatie (1964), Odei (1966), Williams (1969), Mahlau (1970), Kajubiri et al. (1977) and Obiamiwe (1977).Studies of its life cycle including the molluscan hosts are very sketchy and speculative in most cases.This situation contrasts sharply with Dicrocoelium dendriticum.a closely related species where almost thirty snail species and several arthropods were listed by Soulsby (1965) as intermediate hosts in Europe, America, Asia and North Mrica.
Limicolaria and Achatina were suggested as possible snail hosts of D. hospes in Ghana (Odei 1966) while Bourgat et al. (1975) found larval stages of the trematode from Limicolaria/lammea.L. striatula and L. aurora collected from grazing fields in Togo.In Sierra Leone, however, Asanji (1976) failed to infect experimentally any of these snails, although the country shares similar geographical and ecological features with Ghana and Togo.It is therefore important to establish the hosts of the fluke in Nigeria for a good understanding of its epizootiology.

Materials and Methods
Eggs of D. hospes were recovered from the gall bladders of infected cattle or teased out of the uterus of adult worms.They were incubated to full embryonation using the method of Fashuyi (1984).Samples of Limicolaria /lammea.L. striatula.an unidentified Limicolaria sp. and young Achatina sp. were collected from the Biological Garden of the University of Lagos while colonies of Lamellaxis gracilis were raised in the laboratory.Adult Achatina sp. was purchased from open markets in Lagos.Several snails from each sample collected from the Biological Garden were dissected and examined for trematode infection.
Exposure of snails to infection was carried out by isolating them in groups of five in plastic cans containing food mixed with over one hundred fully embryonated eggs for 48 hours on each occasion.Seven days after exposure, 1 -2 snails of each type were dissected daily and examined for any possible trematode infections.Mature cercariae were studied live but measurements were taken from twenty specimens fixed in hot 10 % formalin." Snails were maintained in the laboratory on fresh or decaying paw paw {eaves, lettuce and occasionally moist humus In the case of L. gracilis.

Examination of Snails Collected from Natural Conditions
A total of 50 Limicolaria flammea, 42 L. striatula and 30 unidentified Limicolaria sp.collected from the Biological Garden were examined without finding trematode infections.Similarly, none of the 25 adult and 10 young Achatina sp.examined without exposure to embryonated eggs of D. hospes was infected by trematodes.Both the mother and daughter sporocysts were recovered from the digestive glands of infected snails.The minimum period for occurrence of mature cercariae in L. jlammea was 16 days after exposure.The highest number of mature cercariae recovered: from the ; snail was 40.Other snails contained between 15 and 20 mature cercariae each when dissected.However, over 80 developing cercariae have been counted from few mother sporocysts of all species of infected snails.Mature cercariae were still recovered : from L. striatula 72 days after exposure.Most of Lamellaxis gracilis population exposed to infection died out after 46 days or were never infected.Few had empty sporocysts.

The Cercaria of D. hospes
The mature cercaria has a semi-transparent body, 1.7-2.0mm x 0.5-0.7 mm; and .' short' tail.The oral sucker measuring 0.3-0.4mm in diameter bears a stylet, while the ventral sucker is 0.16-0.24mtn.across.The pharynx measures 0.11 to 0.15 mm x 0.16-0.20 mm The fume cell formula and pattern of integumentary papillae are similar to the description of B 0 u r gat et al. (1975).

Discussion
The cercariae recovered from laboratory infected snails are similar in size and morphology to those described from naturally infected Limicolaria from togo by Bourgat et al. (Loc. cit.).Although Achatina sp. has been recorded as a host in Ghana by Odei (1966), the results in Table 1 show that this may not be the case in Nigeria because all mature and young snails exposed to embryonated eggs never showed signs of infection.A similar experience was encountered by Asanji (1976) in Sierra Leone.The most attractive of all the snails used for this experiment is Limicolaria jlammea in which infections reached maturity within J 6 days and which also produced largest number of mature cercariae.However, the fact that the unidentified species of Limicolaria was refractive to infections shows that D. hospes is host specific to some extent.
The development of D. hospes larvae in Lamellaxis gracilis has not been mentioned in any literature.The snail is much smaller in size than either Limicolaria or Achatina.It is known to be the first intermediate host of Mesocoelium monodi, a common parasite of amphibians and reptiles in West Africa (Thomas 1965).The trematode is a member of the Dicrocoeliidae (Bayssade -Dufour and Bourgat 1975).
Although a very low rate of 8 % infection was recorded from the snail, its potential as a natural vector seems higher than Limicolaria.Lamellaxis has been observed to occur in both rain forests and savannah zones throughout W. Africa (Asanji loco cit), unlike Limicolaria which is essentially a rain forest snail.The cattle rearing areas of Nigeria are mostly in the savannah regions with long dry seasons.This does not however rule out the possibility of occurrence of Limicolaria throughout the year around the river valleys and water holes which form areas of concentration of cattle during the dry season.

Table 1
Reoultll of SnaillDfe.tionlAfterE~ur.toEmbryonatedelll of D. hollpelInfection of Snails Exposed to D. hospes EggsThe results obtained after exposure of snails to embryonated eggs are presented in Table1.Larval stages of D. hospes developed to maturity in Limicolariaflammea, L. striatula and Lamellaxis gracilis.Both young and adult Achatina sp. and Limicolaria sp. were uninfected.The highest rate of infection of, 30 % was recorded in L. flam-mea, followed by 20 % infection in L. striatula.Only 8 % of Lamellaxis gracilis exposed to embryonated eggs had D. hospes infections.