Fasciola Proj. DOCUMENT 2 – Goal 1: SNAIL SURVEYS (3rd Quarter - Oct 2015)
MILKSA Third Quarterly Report:
Project: Impact of Fasciola hepatica on Dairy Production and Sustainable Management on
Selected Farms in South Africa
Note: this report principally comprises updated graphs of the Quarter 2 report.
A standardised method was developed, and a comprehensive Fasciola intermediate snail host
survey conducted for each of six previously selected marshy sites (potential snail habitats) on
each of four farms, selected for either presence or absence of fasciolosis as an important animal
health condition. Of importance is that:
(i) The spots were previously selected on the strength of investigation of practically all likely
points of transmission of the parasite on each of the farms, with the six most promising ones
then selected in relation to the numbers of snails recovered per site;
(ii) An urgent requirement was to enable the conduction of surveys during inclement weather,
i.e. principally rainfall and excessive wind, over the course of the visits to the farms, since visits
need to occur monthly to get an indication of the seasonal cycling of the parasites and
intermediate hosts and as last-minute changes to reserved flights is extremely expensive. A
procedure was duly developed and preparations made and tested to good effect in the face of
rain and mild wind during the past three visits.
Life cycle of trematodes, including Fasciola (liver fluke) and paramphistomids (conical fluke):
Irrespective of whether the trematodes are situated in the liver or the rumen of their hosts, their
eggs are voided in the faeces, on pasture. While the eggs can survive for long periods in the faeces,
they can only develop further once they have landed in open water, in which the eggs hatch and the
emerging larval stage (miracidium) penetrates into the intermediate snail host where it reproduces
asexually to give rise to very large numbers of the final larval stages, the cercariae. The latter emerge
from the snail in open water before they attach themselves to objects (most commonly plants of any
species) and undergo transformation into the infective stage, evident as almost microscopically small
cysts, the so-called metacercariae, which can survive for relatively long periods in moisture until
ingested by their final hosts. Once inside the cattle, the microscopically small parasites emerge from
the cysts, migrate through the wall of the small intestine and along the lining of the abdominal
cavity, bore their way into the liver and literally eat their way through the liver tissue over some
weeks, until they penetrate the bile ducts, where they mature and commence egg laying. The adult
flukes can live even up to some years in their hosts, during which time the host remains largely
susceptible to re-infection.
Method of snail survey being conducted: Of special relevance, is that all the sampling sites on the
different farms were selected by JvR, who has a great deal of experience not only of selection of
such sites in general, but in particular also on dairy farms in the region where the present project is
being conducted.
With the help of household sieves, more or less 8cm in diameter, mud is scooped up from 10 sites
per selected marshy pool per farm, and carefully sieved on a special sieve welded and prepared by
JAvW according to a plan provided by Dr Vic Hamilton-Attwell, a snail expert from the University of
Stellenbosch. As far as possible the snails recovered in the process are counted and identified and
mostly returned to their sites of origin, in order not to disturb the populations by monthly sampling.
However, in cases where large numbers of snails are encountered per site, some of them are
sampled for examination, aimed at determining whether or not they are infected with either
Fasciola sp. or paramphistomid parasites.
Intermediate host snail species: The two species of snails potentially of importance for transmission
of liver fluke in the Tsitsikamma region, are Lymnaea truncatula and Lymnaea columella (introduced
half a century ago from the USA). However, at present it is uncertain to what extent the latter
species is of importance for liver fluke transmission in relation to L. truncatula. In the case of the
conical fluke, the principal intermediate host in most of South Africa is Bulinus tropicus, although it is
known from work done abroad, that L. columella can also serve as intermediate host to the fluke.
In the absence of rain, the snails progressively penetrate into the drying mud, where they can
survive for months until it has rained sufficiently to “revive” the marshy conditions in which the
snails thrive. In other words, rain or the absence thereof can be expected to have a profound effect,
in relation to the time of sampling, on the extent to which the snails are recoverable from samples of
mud.
The results of the snail surveys are presented in the following series of graphs.
The first two graphs per farm respectively show the numbers of L. columella and L. truncatula snails
recovered per selected sampling site. In the remaining two graphs per farm, on the other hand, the
numbers of small snails are shown separately per farm from the totals for all six of the selected sites.
While the first two graphs per farm illustrate the total numbers of snails of the two species
recovered, the last two are more detailed, in that they list the results of individual sampling sites,
but to the exclusion of those sites from which no or only the occasional snail, were recovered.
Of importance in the graphs is not only the large amount of variation between farms, but also that
between the different sampling sites per farm. Not only were very few snails found on Farm III, but
even on the farms where relatively large numbers of snails were found, there were large differences
in the numbers encountered per snail surveillance site.
FARM I
Plaas (I) : L.truncatula
100
80
60
1
3
4
6
40
20
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (I) : L.columella
60
50
40
30
20
10
0
1
2
3
4
5
6
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (I) : L.truncatula
250
200
Klein
150
Totaal
100
50
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (I) :
60
50
40
Klein
30
Totaal
20
10
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
While only very small proportions of the snails from Farm 1, of those investigated in the laboratory,
have been found to be infected with either of the two different types of trematode parasites, on the
last sampling occasion both the faecal egg counts, as well as the number of snails infected with the
paramphistomid parasites (conical fluke) has risen. This signifies that particularly the young cattle
will need to be closely tended as regards untoward diarrhoea, in excess of that expected from the
state of the pastures.
===================================================================
FARM II
Plaas (II) : L.truncatula
70
60
1
2
3
4
5
6
50
40
30
20
10
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (II) : L.columella
20
15
1
2
3
4
5
10
5
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (II) : L.truncatula
160
140
120
100
80
60
40
20
0
Klein
Totaal
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (II) : L.columella
25
20
15
Klein
10
5
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
FARM III
Plaas (III) : L.truncatula
1
0.8
1
2
3
4
5
0.6
0.4
0.2
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (III) : L.columella
12
10
1
2
3
4
5
8
6
4
2
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (III) : L.truncatula
1
0.8
0.6
Klein
Totaal
0.4
0.2
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (III) : L.columella
25
20
15
Klein
Totaal
10
5
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
FARM IV
Plaas (IV) : L.truncatula
120
100
80
60
40
20
0
1
2
3
4
5
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (IV) : L.columella
70
60
50
40
30
20
10
0
1
2
3
4
5
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (IV) : L.truncatula
160
140
120
100
80
60
40
20
0
Klein
Totaal
Apr
Mei
Jun
Jul
Aug
Sept
Okt
Plaas (IV) : L.columella
70
60
50
Klein
Totaal
40
30
20
10
0
Apr
Mei
Jun
Jul
Aug
Sept
Okt
The snail survey results are still very preliminary, in that much variation is to be expected from
month to month, owing to climatic factors, mainly rain and temperature, on the one hand, and
immediate effects such as the length of time since the pasture has been grazed, and the degree of
trampling of the survey sites per farm by grazing cattle. In other words, because of the short
duration of monthly sampling to date, the present results cannot be regarded as of great significance
as yet in relation to seasonal cycling and prevalence to be expected over the course of the survey.
On the other hand, it is clear that relatively large numbers of snails were recovered on some of the
farms, up to close to 115 on a single sampling occasion from a single site (marshy spot) on one of the
farms, over against no L. truncatula snails (the principal intermediate host of F. hepatica) and only a
handful of L. columella recovered from Farm III over the total of seven sampling occasions.
Graphs: numbers of snails: While the first two graphs per farm list the total numbers of snails of the
two species recovered per farm, the last two are more detailed, in that they list the results of
individual sampling sites, but to the exclusion of those sites from which no snails, or only the
occasional one, were recovered.
Of note in the graphs is not only the large amount of variation between farms, but also that between
the different sampling sites per farm. Not only were very few snails found on Farm III, but even on
the farms where relatively large numbers of snails were found, there were large differences in the
numbers encountered per snail surveillance site per occasion.
Infection of snails with parasites: Investigative evaluation of a few snails over the period for the
presence of Fasciola (liver fluke) and paramphostomid parasites (conical fluke, probably
Cotylophoron sp.), was done for confirmation of the genera/species of the parasites in the
snails. After morphological identification, samples were preserved for later DNA confirmation
towards the end of Phase 1 of the project. In order not to influence the epidemiological data on
the seasonal cycling of the intermediate hosts of the parasites, the vast majority of the snails are
returned to their sites of collection after they have been counted; only small numbers are
collected for evaluation of levels of infection, and only from collection sites where relatively
large numbers of the snails are encountered at any given time.