SECTIONAL TRANSACTIONS.— D. 337 



Dr. Annie Porter.— Some South African Larval Flukes. 



Bilharziasis is a serious disease in South Africa, and for some years examinations 

 of the larval Trematoda in freshwater molluscs with a view to determining the 

 invertebrate hosts for human Schistosomes have been conducted. Other larval 

 flukes have been observed and are more numerous than those of schistosomes. Most 

 attention has been given to the parthenita and cercarise occurring in molluscs proved 

 to transmit human disease ; the other non-schistosome hosts have received less 

 attention. Schistosoma hcematobium, the excitant of urinary bilharziasis in man, is 

 transmitted chiefly by Physopsis africana and to a much less extent by Physopsis 

 globosa, Isidora tropica and Limncea natalensis. Schistosoma mansoni, the excitant of 

 bilharzial dysentery, is much less common in the Union and is transmitted by 

 Planorbis pfeifferi, Physopsis africana and Isidora tropica. Schistosoma spindalis, a. 

 rare human parasite, has Planorbis pfeifferi and Isidora tropica as moUuscan hosts. 

 S. bovis, not yet found with certainty in man, but causing epizootics among sheep, is 

 harboured by Physopsis africana. An adult schistosome, agreeing morphologically 

 with Schistosomatium pathlocopticum, has been bred in the laboratory from cercarise 

 from Limnma natalensis. Cases of human infestation with Fasciola gigantica and 

 F. hepatica have occurred in South Africa and the cercarise of F. hepatica 

 occur in Limncea natalensis and those of F. hepatica in Isidora tropica, 

 Limncea natalensis and L. truncatula, Isidora tropica being the most common trans- 

 mitter. Cercariae of Paramphistomum calicophorum and of P. bovis are found in 

 Isidora tropica. Schistosomes and liver flukes are of much economic importance. 

 Cercarise of unknown adult schistosomes occur in very small numbers, and often as 

 infections of one snail only, in all the transmitters of the human blood flukes. Further, 

 both Physopsis africana and Planorbis pfeifferi harbour cercarise that superficially 

 resemble those of man, but are really unidentified Monostomes with forked tails. 

 Some monostome cercariae have been observed. A number of species of Echinostome 

 larvae have been obtained, mostly from Limncea natalensis but some from Physopsis 

 and Planorbis. One such was experimentally determined as Echinosiomiim fulicce, 

 parasitic in the redknobbed coot, the larvse having been obtained from Tomisia 

 ventricosa and Isidora tropica. The agamodistome stage of another echinostome is 

 passed in the skin of Xenopus Ice vis and for purposes of reference has been termed 

 E. xenopi. Xiphidiocercarise are fairly numerous, particularly in Physopsis africana. 

 Some interesting cystophorous cercarise occur in Planorbis pfeifferi, and various 

 Ancylidse contain monostome and cystophorous cercariae. 



The cercarial fauna of the Transvaal shows differences from that of Natal and the 

 Cape, though some species are common to all. Human schistosomes have not been 

 found hitherto in snails from Basutoland, the Orange Free State and the Western 

 Cape. They are restricted to Natal, the Transvaal and the Eastern Cape Province. 

 The same snails are responsible for bilharziasis in Rhodesia and Portuguese East 

 Africa as in the Union. 



It is not uncommon for the same species of cercaria to occur in several different 

 genera of snails, ilixed infections have been observed in some instances. Experi- 

 mental infestations of laboratory animals with human schistosome cercarise often 

 result in a great preponderance of male worms. While the hypothesis is suggestive, 

 there is no real evidence for assuming that all the cercarise from any one mollusc are 

 of the same potential sex. Large and small strains of cercarias are produced owing 

 to differences in the development of the host, abundance or otherwise of the food 

 supply, and amount of space in which development occurs. 



The distribution of snails concerned with human disease depends on the suitability 

 of the water for snail development, speed of the current, density of the human 

 population, degree of pollution of the water and the presence or absence of enemies of 

 moUuscan life. 



Dr. F. G. Causton. — Physopsis africana, distinct from Isodora (Bulinus). 



Dr. Annie Porter. — Some Remarks on the Hookworm Problem in South 

 Africa. 



Hookworm disease in South Africa is due to both Ancylostoma duodenale and Necator 

 americanus. It is localised and not endemic . It appears to be restricted to some sugar 

 areas in Natal and to mining areas in the Transvaal, in each case being intimately 

 1929 2 



