1. RESULTS
INTRAMOLLUSCAN STAGES OF E. paraensei IN Biomphalaria
B. glabrata AND B. pfeifferi, HOST SUITABILITY FOR E. paraensei
VG = Brazilian B. glabrata, Bp = African B. pfeifferi, M = M line B. glabrata
Snail mortality after exposure to E. paraensei.
Relative number of parasite stages Infection prevalence
observed from B. glabrata and B. pfeifferi in B. glabrata and B.pfeifferi
ABSTRACT
Digeneans, diverse flatworm parasites (flukes), impact veterinary and human health globally. e.g. Schistosome parasites infect over 200 million humans causing the debilitating infectious disease schistosomiasis. Flukes must first infect a snail intermediate host to develop before the snail can transmit these parasites to vertebrates. Genetic factors define the complex fluke-snail associations and host suitability is restricted to species, strain or even individual level. Study of host suitability can help understand and control epidemiology of snail-transmitted flukes. At UNM, the South American digenean Echinostoma paraensei is maintained using M line Biomphalaria glabrata, a neotropical snail species as intermediate host. The suitability as host for E. paraensei of two Biomphalaria field isolates was tested; VG strain B. glabrata (Brazil) and an African species, Biomphalaria pfeifferi. Although B. glabrata and B. pfeifferi are distinct species from different continents, they are close relatives. African Biomphalaria species evolved after a neotropical ancestor of B. glabrata colonized Africa between 1-5 million years ago. During this interval, B. pfeifferi has not likely encountered E. paraensei. Juvenile Biomphalaria were exposed to 20 miracidia each, snail survival and parasite development were monitored weekly (using M line B. glabrata as control). Exposure yielded elevated mortality but no parasites developed in VG B. glabrata. Remarkably, B. pfeifferi proved a suitable host for E. paraensei, releasing cercariae at 4-5 weeks post-infection. Biomphalaria glabrata may not always be suitable, but E. paraensei finds a competent intermediate host in B. pfeifferi after a million years of speciation that separate African from South American Biomphalaria snails.
Once in a million years—testing Biomphalaria snail host suitability for the parasite Echinostoma paraensei.
Zachary T. Barnes, Larry M. Benjey, Molly E. Benning, Gabriela Chacon, Ashley Clark, Jennifer L. Cooksey, Amre Elmaoued, Stephanie J. Finley, Ferriell A. Henry, Raquel S. Hill, Jaron J. Kee, Keith Keller, Ashley Liserio, Michael A. McKitrick, Audrey L. Melton, Ngoc-An T. Nguyen, Michelle A. Sandoval, Jonathan Schultz, Vanessa Surjadidjaja, Hsin Lung Tsai, Martina Laidemitt, Coenraad M Adema.
OBJECTIVES
To determine whether after > 1,000,000 years of speciation, African Biomphalaria pfeifferi (collected from Kenya, now maintained at UNM) is a suitable host snail for the South American parasite Echinostoma paraensei.
To determine whether field-collected (VG) B. glabrata is a suitable intermediate host for the South American parasite Echinostoma paraensei.
CONCLUSIONS
The E. paraensei parasites were viable and infective, yielding standard infection rates and parasite development in M line B. glabrata, routinely used in the lab as 1st intermediate snail host.
Field-collected (VG) Brazilian B. glabrata did not develop patent infections after exposure to E. paraensei miracidia. Increased snail mortality versus M line suggests negative impact from penetrating parasites.
A proportion of field-collected African (Kenya) B. pfeifferi is suitable as 1st intermediate host snail for E. paraensei. Infection yields viable cercariae that establish as metacercariae in 2nd intermediate host (M line B. glabrata) snails. Prevalence was reduced relative to M line controls. Mortality of lab-maintained B. pfeifferi is routinely high.
FUTURE DIRECTIONS
Experiments are to be repeated to confirm these observations, using additional batches/isolates of snails and E. paraensei.
The yield of parasites and timing of cercarial release will be tested for the African (Kenya) B. pfeifferi snails relative to M line B. glabrata.
VG Brazilian B. glabrata will be exposed to E. paraensei and monitored for presence of parasites, snail mortality, parasite virulence, and host immune responses in response to E. paraensei parasite infection.
ACKNOWLEDGEMENTS
This poster is presented in partial fulfillment of requirements for course 482L/ 582L, Parasitology, Spring semester We appreciate the facilities offered for course (perhaps the micro-scopes could be better), including the snails and numerous parasites used in the study. Thanks to all, especially Dr. Si-Ming Zhang, who collected snails from the field (particularly B. pfeifferi) and maintained snails and parasites in the laboratory.
Photographic representation of the development of intramolluscan larvae of E. paraensei in either M line B. glabrata or B. pfeifferi (B.p) as 1st intermediate host and M line B. glabrata as 2nd intermediate host. Scale bars:100mm.
Note, this project only focused on parasite development in the (invertebrate) snail hosts, it did NOT involve the definitive host (hamster).
MATERIALS AND METHODS
Juvenile snails, from M line Biomphalaria glabrata (lab strain control), Brazilian field isolate (VG) Biomphalaria glabrata, and African (Kenya) field isolate Biomphalaria pfeifferi, were individually exposed to miracidia of the parasite E. paraensei.
Snail survival and parasite development were monitored weekly by observation and dissections.
To test parasite viability, cercariae from patently infected snails (1st intermediate host) were tested to see whether they could infect M line B. glabrata as 2nd intermediate host. After exposure, snails were inspected for pericardial metacercariae.
BACKGROUND
Egg
Miracidium
(M line w.) sporocysts in heart (also observed from BB02)
Mother Rediae
Daughter Rediae
Cercariae
Metacercariae (in M line B. glabrata)
Final host
2nd intermediate
host
1st intermediate host
B.p
B.g
Phylogenetic analyses show close genetic kinship in support of the hypothesis that an ancestor of New World B. glabrata colonized Africa ~1-5 million years ago and gave rise to all African Biomphalaria species, including B. pfeifferi (Dejong et al, 2003; Map of Africa from Jorgesen et al, 2007).
It is unlikely that African Biomphalaria such as B. pfeifferi have ever encountered the South American digenean E. paraensei, a parasite specific for B. glabrata.
1-5 million years ago
VG, M line B. glabrata
B. pfeifferi + - ++
Mother / Daughter Redia
not determined
Sporocysts Bp VG M
strain
stage
13/16 (includes 1 dead snail)
3/8
Cercariae (Shedding/ snails tested)
11/12
2/3
Metacercaria (following exposure of M line snails)
28/30
8/10
0/15
Infected (positive/ dissected) 50 30
Exposed
week 6
week 5
week 4
week 3
week 2
week 1
Cumulative mortality for each snail strain, at weekly intervals post exposure to E. paraensei.
30 B. pfeifferi snails, 50 of each B. glabrata strain were exposed. Values do not include snails that were dissected (15 VG, 10 Bp, 30 M).
Week post exposure
% cumulative mortality
South America
Africa