Evaluation of the Crayfish, Procambarus Clarkii as a Bio-control Agent Against Schistosome-Transmitting Snails in Stream Habitats within the River Athi Basin

Abstract

Schistosomiasis is a water-based snail-transmitted parasitic disease. More than 210 million people are currently thought to be infected world-wide. Although several approaches can be applied for schistosome control, chemotherapy is the most commonly used and recommended by WHO. Praziquantel is the only drug available for individual case management and for mass treatment. The main objective of this study was to determine the ability of the crayfish, Procambarus clarkii to control schistosomiasis in stream habitats in the Machakos County within the Athi river basin. Planorbids snails were collected at random from the single stretches of the stream sectors using scoops, placed in 24 well culture plates, counted and shed to determine infected snails while crayfish were trapped using onion bag net traps from Lake Naivasha and translocated into 2 experimental streams. Out of 2325 total sampled snails, 161 turned out to be positive for mammalian schistosomes following shedding of cercariae representing a prevalence of 6.9%. The pH, water and temperature did not vary significantly in the different streams (P-value = 0.7524 at P>0.05). Increase in water temperature showed significant positive correlations with B. pfeifferi (r2 = 0.665; P < 0.01) and B. nasutus (r2 = 0.0.665; P < 0.05) Lymnea natalensis (r2 = 0.589; P < 0.010). The overall mean pH value was 7.8 ± 0.8 with values ranging from 7.34 in Kwa Mutanga River to 8.6 recorded in Kyanguli River. Snail abundance in habitats in which crayfish were introduced rapidly declined within 2 months to a significant level (paired t test = 5.524, p value = 0.0001), relative to the decline observed in the control habitats (paired t test = -7.727, p value = 0.082. Crayfish and snail sampling record forms was used to collect the data for the snails and the crayfish respectively. Data analysis was done using SPSS Version 21.0. The findings showed that the relationships between water temperature and snail abundance varied with different species of snails Biomphalaria pfeifferi and Bulinus nastus (16.7%), Lymnea natalensis 6.7%. This study indicates that crayfish can establish and form thriving population; especially where the water velocity was low. Crayfish reduced schisto-transmitting snail B. pfeifferi and B. nastus. While P. clarkii holds much promise as a supplementary schistosomiasis control strategy, the effect of abiotic and biotic factors on the predator should not be ignored when planning biological control interventions.