Brachylaima spp. (Digenea: Brachylaimidae) are terrestrial trematodes of mammals and
birds and have land snails as their first and second intermediate hosts. This thesis describes
a new species of Brachylaima and investigates infection in both snail intermediate hosts
and definitive host animals. A laboratory life-cycle was established using brachylaimid
eggs recovered from the faeces of an infected human. Five species of introduced European
helicid and hygromiid snails, Theba pisana, Cernuella virgata, Cochlicella acuta,
Cochlicella barbara and Microxeromagna armillata were susceptible first intermediate
hosts. These same snails and introduced Helix aspersa as well as the native snails Succinea
australis and Strangesta gawleri were suitable second intermediate hosts. Field and
laboratory studies revealed that in addition to humans and mice, various species of birds
and reptiles were also definitive hosts. On the basis of its unique morphological and lifecycle
features, a new species, Brachylaima cribbi was described. The scanning electron
microscopical appearances of the various life-cycle stages were detailed. Studies of Swiss
albino outbred mice and 8 strains of inbred mice revealed that C57BL/6J mice were most
susceptible to B. cribbi infection. The peak infection occurred 4 weeks after inoculation
with metacercariae following which worms were expelled over the next few weeks.
Exposure to a second infection in C57BL/6J mice did not result in accelerated expulsion of
adult worms but did significantly inhibit their fecundity. In contrast, when
immunodeficient NOD SCID mice were infected with B. cribbi metacercariae the adult
worms persisted for the life span of the host mice. 6,432 land snails were collected over a
distance of 3,000 km across southern Australia. Sporocyst-infected snails were found in all
districts of South Australia and Victoria with the percentages of infected T. pisana, C.
virgata, C. acuta and C. barbara ranging from 1.7 to 4.7%. These 4 species together with
M. armillata, S. australis and S. gawleri were infected with metacercariae being found in
18-63% of snails and the mean number of metacercariae per infected snail ranged from 2.1
to 6.1. Laboratory studies revealed that eggs may remain viable for almost 12 months in
mouse faeces. The prepatent period for a sporocyst infection is 7-10 weeks after egg
ingestion. Metacercariae 7 weeks of age are capable of developing into adult worms.
Detailed studies of seasonal variations in sporocyst and metacercarial infection rates were
studied at 4 ecologically diverse sites on the Yorke Peninsula of South Australia. The
clinical features and epidemiological circumstances of B. cribbi infections of 12 humans
are detailed, as is their satisfactory response to treatment with praziquantel. Thesis (Ph.D.)--School of Molecular and Biomedical Science, 2003.