A Faunistic Survey of Digenean Larvae Infecting Freshwater Snails Biomphalaria, Radix and Bulinus Species in the Lake Victoria and Mindu Dam, Morogoro in Tanzania
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A FAUNISTIC SURVEY OF DIGENEAN LARVAE INFECTING FRESHWATER SNAILS BIOMPHALARIA, RADIX AND BULINUS SPECIES IN THE LAKE VICTORIA AND MINDU DAM, MOROGORO IN TANZANIA Fred D. Chibwana* and Gamba Nkwengulila Department of Zoology and Wildlife Ecology, University of Dares Salaam P.O. Box 35064, Dar es Salaam *[email protected], [email protected], ABSTRACT Biomphalaria and Bulinus spp have been reported in Tanzania as vectors of Schistosoma mansoni and Schistosoma haematobium respectively. Thus most schistosomiasis control efforts have focussed on elimination of these molluscs in freshwater systems or deworming infected persons. In addition almost there is limited information of larval trematodes infecting freshwater snails in Tanzania and whether the trematode antagonism found elsewhere could be used for control of schistosomiasis. We report and describe larval digeneans infecting Biomphalaria pfeifferi, Bulinus spp and Radix natalensis, snails collected at Mindu dam, Morogoro and Mwanza gulf of the Lake Victoria from January 2011 to January 2012. Out of a total 9194 snails, belonging to Biomphalaria pfeifferi, Bulinus tropicus and Radix natalensis, collected from Mindu dam and the Mwanza gulf, Lake Victoria, 678 (7.34%) were infected with 14 larval trematode species: 3 xiphidiocercariae, 6 furcocercariae, l gymnocephalous cercariae, 1 amphistome, 2 echinostome and 1 undescribed metacercaria. From 386 infected B. pfeifferi 67 (1.69%) were infected with S. mansoni, the causative agent of intestinal schistosomiasis. These findings show that despite the increased effort to control schistosomiasis and other neglected tropical diseases in Tanzania, the diseases are still highly prevalent in freshwater systems. However, the absence of trematode antagonism or low multiple infections mean redia cannot coexist with sporocysts, hence can be used for control of schistosomiasis. Keywords: Bulinus, Biomphalaria, Radix, Digenean larvae, neglected tropical diseases INTRODUCTION al. 2000). Other trematodes such as liver The trematodes, along with the cestodes and flukes Fasciola, Clonorchis, Opisthorchis monogeneans constitute the subphylum and lung flukes Paragonimus species are Neodermata within the phylum obtained from the consumption of raw or Platyhelminthes (Cribb et al. 2003); have a undercooked freshwater plants, crabs, fish or cosmopolitan distribution and are implicated shellfish of many species with infective in some of the most important parasitic metacercariae (Abdussalam et al. 1995; Sun diseases of man and animals. The et al. 2011). These parasites cause classification of trematode groups is largely devastating impacts on human, veterinary based on their habitat in the host (liver, lung, and aquaculture health resulting in slower intestine) (Chai et al. 2005). The most economic growth. common ones, in the tropics and subtropics in particular, are the blood flukes of the It is worth noting that freshwater snails play genus Schistosoma the agents of a key role in the transmission of these eye- schistosomiasis (or bilharziasis) (Chitsulo et catching digenetic trematodes. The snails Chibwana and Gamba - Faunistic survey of digenean larvae infecting freshwater snails … provide the parasites with not only the foodborne zoonotic trematodiases, and those nutrients and space for reproduction but also of less medical or veterinary importance. transport by which the parasites can proceed The only all-inclusive studies known on to infect the next host generation (Lockyer et larval digenean are those carried out by Fain al. 2004). The peculiarity of the snail- (1953), Vercammen – Grandjean (1960), trematode guild comes from the fact that the Loker et al. (1981), King and Van As (2000) majority of the known digenetic trematode Chingwena et al. (2002), Nkwengulila and species utilize snails as the mandatory first Kigadye (2005) and Moema et al. (2008). intermediate host (Littlewood and Bray However, these studies covered only small 2001). Snails become infected after eating geographical areas thus leaving out the eggs that are associated with the droppings majority of freshwater snails unattended. In of the definitive host, or after the penetration addition, Loker et al. (1981) and by the free-swimming miracidia hatched Nkwengulila and Kigadye (2005) who from eggs (Cribb et al. 2003). In the snail carried out their studies in Tanzania, did not hosts, trematodes multiply asexually to identify all the cercariae recovered from the produce large quantities of morphologically freshwater snails. distinctive larvae (sporocysts and/or rediae), which give rise to cercariae that escape the In the present study we provide data on the snail hosts and disperse in the external abundance, morphology and taxonomy of environment actively locating and penetrate larval trematodes occurring in three the next host or encyst on vegetation. Thus freshwater snails (Bulinus spp, examination of naturally infected freshwater Biomphalaria pfeifferi and Radix natalensis) snails increases the possibility of collected from Mwanza Gulf, Mwanza and understanding (i) the sources of infection of Mindu dam, Morogoro. This is a preliminary the second and definitive hosts (Faltýnková step to defining the snails that harbour et al. 2007, Żbikowska and Nowak 2009), digenetic trematodes of medical, veterinary (ii) the larvae trematodes that may act as or economic importance. It was also regulators of snail populations in high expected that the study would identify the infections (Loker et al. 1981, Brown et al. unidentified trematodes species reported by 2005), (iii) the useful trematodes for Loker et al. (1981) and Nkwengulila and biological control of snail transmitted Kigadye (2005) as well as highlighting the diseases (Davis 1998) and (iv) the bio- status of schistosomiasis and possible use of indication of environmental quality (Kuris other digeneans (see Davis, 1998) to its and Lafferty 1994, Keas and Blankespoor control in Tanzania and thus provide a 1997). useful baseline information for future studies. Several studies of larval trematodes have been carried out in Europe for over a MATERIAL AND METHODS hundred years (Faltýnková et al. 2007, 2008, Snail collection Żbikowska and Nowak 2009). On the Field work involved the collection of three contrary, in Africa these studies are few in most common genera of snails number and most of them have been Biomphalaria, Radix and Bulinus, of which restricted mainly to schistosomiasis (Kasuku two, Biomphalaria and Bulinus, have been et al. 1988) and fasciolisis (Ogambo- implicated in the transmission of Ongoma 1971), while there is relatively little schistosomiasis (Brooker 2002). The information on the abundance, morphology, specimen of the snails, Biomphalaria and taxonomy and even host relationships of Radix spp. were collected from the Mwanza other trematode species responsible for Gulf of Lake Victoria (situated at 2º 41′ S 2 Tanz. J. Sci. Vol. 43(1), 2017 and 32º 51′ E) and Bulinus spp. were snails collected from each site were then collected from Mindu Dam, Morogoro (37º experimentally subjected to cercarial 36′ E and 6º 50′ S) in Tanzania (Fig. 1), emergence by placing them separately in from January 2011 to January 2012. The small vials of 12.5 ml or 50 ml under a snails were mostly found in places where strong artificial light and heat (60W) for a water was stagnant or slowly moving, and period of 6 to 48 hours. Both cercariae were collected using a strainer or located emergence and snails with no emergence visually and handpicked from underneath of were crushed between two glass slides and waterweeds on the shores (Faltýnková examined for intramolluscan stages. At 2005). Snails collected from each site were Mindu Dam Biomphalaria and Lymnaea placed in separate labelled plastic containers could not be found, thus only Bulinus spp. with water from the site and lettuce or were collected. Because of some difficulty Chinese cabbage; and transported to the in separating Bulinus species (see laboratory where they were placed in small Mukaratiwa et al. 1998, Brown 2005), aquaria containing dechlorinated water and bulinid species were not classified to species fed with lettuce or Chinese cabbage. The level. Figure 1: Map of Tanzania showing study sites (Mindu dam and the Mwanza gulf, Lake Victoria). 3 Chibwana and Gamba - Faunistic survey of digenean larvae infecting freshwater snails … Morphological studies and identification of two localities while xiphidiocercariae had snails and digenean larvae the highest prevalence as (Table 1). The snails were identified based on field guides proposed by the Danish Bilharziasis In the Mwanza gulf Bulinus species were not Laboratory (1987) and Brown (2005) for abundant, and when they were found they Africa freshwater snails. The cercarial had no infection. On the other hand, Bulinus morphology was studied from live specimen species were abundant at the Mindu dam and emerging from the snails using neutral red about 7.65 % of the collected samples were and Nile blue solution as intravital stains and infected either with furcocercariae (1.32%) observed under light microscope. or echinostomes (6.33%). However, from Measurements were taken from specimen the recovered furcocercarial forms placed in a drop of water and killed by heat Schistosoma species were absent. On the (Niewiadomska and Kiseline 1994). The contrary, Radix and Biomphalaria species digenean larvae were identified based on were absent at Mindu dam, but were keys by Miller (1926), Nasir and Erasmus abundant at the Mwanza