Download MILKSA Fasciola-Progr.Rep.4-Snails

[2016/03/06]
th
Fasciola Proj. DOCUMENT 2 – Goal 1: SNAIL SURVEYS (4 Quarter-Dec. 2015)
MILKSA Fourth Quarterly Report
Project: Impact of Fasciola hepatica on Dairy Production and Sustainable Management on
Selected Farms in South Africa
Note: For the sake of comprehensibility, quarterly reports in the project largely comprise
sequential addition of new information and updating of graphs.
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 project farms, selected for either presence or absence of fasciolosis as an important
animal health condition.
Life cycle of trematodes, including Fasciola (liver fluke) and paramphistomids (conical fluke): For
both of these groups of trematodes the life cycle can only be completed, with resultant build-up of
worm challenge on pasture, if the faecal pats containing the eggs of the worms land up in open
water on pasture. This enables the parasite to gain access to and develop to the infectious stage in,
and later to escape from its intermediate snail host. This infectious stage comprises a small larva,
which also requires open water to be able to gain access to, and encyst on pasture to await ingestion
by cattle, for the cycle to start from the beginning again.
Intermediate snail hosts of importance in the Eastern Cape region: In large parts of the world, as
well as in South Africa Fasciola sp. are transmitted primarily by Lymnaea species mud and semiaquatic snails, namely Lymnaea (Galba) truncatula and Lymnaea columella for Fasciola hepatica .
However, little field work has been done to determine the relative importance of the two snail
species in the transmission of F. hepatica, the species present in the Eastern Cape region (Horak,
1981. Jl S. Afr. Vet. Ass., 201-206).
In the what follows in this report the snail intermediate host species are referred to as the “target
snail species”, excepting when referring to any one of the individual species.
Method of target 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.
Mud is scooped up at monthly intervals, with the help of household sieves, more or less 8cm in
diameter, from 10 sites per selected marshy spot per farm, and carefully sieved on a larger, custommade sieve. As far as possible the snails recovered in the process are counted and identified and
mostly returned to their sites of origin, in order for the monthly sampling not to disturb the snail
populations and thus their epidemiology. However, in cases where large numbers of snails are
encountered per site, a few of them are sampled for laboratory examination, aimed at determining
whether or not they are infected with either Fasciola sp. and/or paramphistomid parasites.
Intermediate host snail species: The two species of snails potentially of importance for transmission
of the two trematode parasites of importance to the project, namely liver fluke and stomach
(conical) fluke in the Tsitsikamma region, are Lymnaea truncatula and Lymnaea columella, of which
the farmer is most important, as also in Europe, the United Kingdom, and Ireland and elsewhere, as
intermediate host for F. hepatica. In the case of L. columella, introduced half a century ago from the
USA (where it is purported to be susceptible to F. hepatica infection), it is uncertain as yet to what
extent it may be of importance in South Africa, in relation to that of L. truncatula, as intermediate
host to the two trematode types. In addition to liver fluke, stomach fluke is regarded by Dr Louis
Hoek and other veterinarians at Cape Cross Veterinary Services practice, as perhaps being as of
much the same importance as liver fluke in the region. However, while the stomach fluke is
principally transmitted by the Bulinus tropicus in South Africa, this snail species is almost absent on
the trial farms, with the result that it is to be expected that L. truncatula and/or L. columella will be
responsible for the transmission of this parasite. On the other hand, while it is known that the
parasite can be transmitted by L. columella, this has apparently not been investigated in South
Africa, so it is of importance that this should also be followed up.
As mud dries out in the absence of rain, the snails progressively penetrate into the drying mud,
where at least some of them 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 monthly sampling, on the extent to
which the snails are physically recoverable from samples of mud, as deduced that the snails are
often visible on top of soft, wet mud after good rains, but not on relatively dry mud.
Graphs of numbers of snails recovered over the year: The results of the snail surveys are presented
in the following series of graphs and tables.
While the first two graphs per farm respectively illustrate the totals of L. truncatula and L. columella
snails recovered from all six sampling sites per sampling occasion, the second pair per farm show
the numbers of snails recovered per sampling site, but to the exclusion of those sites from which no
snails, or only the occasional one, were recovered.
In comparing the graphs for the different farms, it is important to consider not only the shape of
each graph, but also the actual numbers of snails involved (for instance with a range of only 5, to
the maximum of 862 L. truncatula recovered per farm (Table 1, and discussed further below). Also of
importance is the high degree of variation between the different surveillance sites (muddy spots) per
farm per sampling occasion, despite the fact that all of the sites were selected on the strength of
having been judged (from experience) to have considerable potential as snail breeding sites. For
example, not only were very few snails found on Farm III, but even on the farms where relatively
large numbers of snails were recovered, there were consistently large differences in the numbers
encountered per snail surveillance site per occasion.
FARM I
Farm (I) - Snails per muddy patch: L.truncatula
100
90
80
70
60
50
40
30
20
10
0
1
3
4
6
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
[i]
Farm (I) - Snails per muddy patch: L.columella
60
50
40
30
20
10
0
1
2
3
4
5
6
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
(ii)
Farm (I) - Total snails, all muddy patches: L.truncatula
250
200
150
Small
100
Total
50
0
Apr
[iii]
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
Farm (I) - Total snails, all muddy patches: L.columella
60
50
40
Small
30
Total
20
10
0
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
[iv]
Of special note only in the case of for Farm I, is that dramatic earthworks that took place over spring
and early summer, aimed at improved drainage of marshy sites of potential importance for snail
transmission, have radically changed the physical character of each of the sampling sites. It seems
likely that this intervention may have made an important contribution to the dramatic reduction
over spring and summer in the numbers of L. truncatula recovered (Graphs [i] and [iii] above),
especially since the numbers of this snail species remained relatively high throughout the 4th quarter
on Farms II and IV, from each of which relatively large numbers of L. truncatula were recovered.
===================================================================
FARM II
Farm (II) - Snails per muddy patch: L.truncatula
70
1
2
3
4
5
6
60
50
40
30
20
10
0
Apr
[v]
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
Farm (II) - Snails per muddy patch: L.columella
18
16
14
12
10
8
6
4
2
0
1
2
3
4
5
6
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
[vi]
Farm (II) - Total snails, all muddy patches: L.truncatula
160
140
120
100
80
60
40
20
0
Small
Total
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
[vii]
Farm (II) - Total snails, all muddy patches: L. columella
25
20
Small
15
Total
10
5
0
Apr
[viii]
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
FARM III (Selected for the project as being devoid of problems with Fasciola infection)
Farm (III) - Snails per muddy patch: L. truncatula
6
1
2
3
4
5
6
5
4
3
2
1
0
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
[ix]
Note (above) the total of only 5 L. truncatula recovered, all in the same month
Farm (III) - Snails per muddy patch: L. columella
12
1
2
3
4
5
6
10
8
6
4
2
0
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
[x]
Farm (III) - Total snails, all muddy patches: L.truncatula
6
5
4
Small
3
Total
2
1
0
[xi]
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
Farm (III) - Total snails, all muddy patches: L.columella
25
20
Small
Total
15
10
5
0
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
[xii]
Of note and discussed further below regarding contiguous Farms II and III, are the dramatic
differences between them in numbers of L. truncatula snails recovered (respectively 5 and 632 Table 1, below).
FARM IV
Farm (IV) - Snails per muddy patch: L.truncatula
140
120
100
80
60
40
20
0
1
2
3
4
5
6
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
[xiii]
Farm (IV) - Snails per muddy patch: L.columella
70
1
2
3
4
5
6
60
50
40
30
20
10
0
Apr
[xiv]
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
Farm (IV) - Total snails, all muddy patches: L.truncatula
200
180
160
140
120
100
80
60
40
20
0
Small
Total
Apr
[xv]
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
Farm (IV) - Total snails, all muddy patches : L.columella
70
60
50
Small
40
Total
30
20
10
0
[xvi]
Apr
May
Jun
Jul
Aug
Sept
Okt
Nov
Dec
For the comparison of the numbers of snails recovered per farm, Table 1 (below) was drawn up. To
this end, it is important to realise that under the farming conditions in the region where the trial
farms are situated, conditions are suitable for liver fluke transmission over a considerable portion of
the year, consequently with a serious complicating effect on approaches with potential for
management of the parasite.
Table 1: Total numbers of snails detected per farm over 9 months in 2015
Farm
Snail species
TOTAL
L. truncatula
L. columella
1
862
80
942
2
632
61
693
3
5
35
40
4
854
295
1149
Particularly striking from the table and the different graphs, are:
(i) The dramatic differences between Farm 3 and the rest, in numbers of the L. truncatula snail
species, the principal intermediate host of for Fasciola sp. in the region, comprising a total of only
5 snails recovered on Farm 1 over the entire period of 9 months of the survey (April to
December) in 2015, compared to 632-862 from the other three;
(ii) The similarly dramatic differences between sampling sites per farm, despite the fact that, as
mentioned above, each sampling site on each of the four trial farms was selected on the strength
of having been judged to be “ideal” for the presence of the target snails.
(iii) That Farms 2 and 3, respectively with totals of 5 and 632 L. truncatula, are adjacent to one
another, share a lengthy common boundary fence and belong to the same owner, albeit with a
separate manager per farm;
(iv) That the four farms were selected by members of MILKSA for extremes in the prevalence of
problems with the parasite, for instance concerning dairy production; in other words, the large
differences confirm that the aim with this selection has been fully met.
It can be seen from the graphs that L. truncatula peaked in the spring on Farm 1 and 2, on which
similarly large numbers of the snail species were recovered. In contrast, however, the numbers on
Farm 1 dropped to practically nil in December, while they remained high from August through to
December on Farm 2. As discussed above, however, the difference is suspected to be due to
earthworks that took place only on Farm 1. On Farm 4, however, with a similar total number of L.
truncatula as on Farms 1 and 2, the graph had a saw-toothed profile as from May, and with a slightly
higher number recorded for December. Lastly, on farm 3 all of the 5 snails of the species were
recorded in a single month, namely November.
Infection of target snails with liver fluke and conical fluke (Table 2) : With the exception of
instances where very large numbers of snails were recovered on any given farm, only small numbers
of snails were harvested for laboratory evaluation, with the vast majority being returned to their
sites of origin.
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 types of the parasites in the snails, and the results are summarised in Table 2
(below). After morphological identification, samples were preserved for later DNA confirmation
towards the end of Phase 1 of the project.
In agreement with the results of faecal egg counting, some of the snails that were harvested from
Farm I for laboratory investigation were found to be infected with either one or the other of the two
different types of trematode parasites being investigated (Table 2). While the identification of the
parasite species encountered in the harvested snails need to be confirmed by further testing, the
indications are that both trematodes that are represented in the faecal egg counts do occur, but
thus far only 39 of the 340 L. truncatula snails examined, were found infected. Furthermore, while
only 4 of the 39 infected snails apparently harboured Fasciola parasites, this is to be expected, since
more than tenfold the numbers of the Paramphistomid than Fasciola worms are required for a
similar production effect on their hosts. In contrast to the situation in L. truncatula, none of the 75 L.
columella evaluated was found to be infected with any trematode parasite. However, the fact that
relatively small numbers of these snails were evaluated, has the implication that more of them will
need to be evaluated before it can be concluded that they do not play a role in the transmission of
the two trematode genera in the region. A further implication of the above results is that, as
emphasised by dr Louis Hoek, conical fluke will need to be kept in mind as possible cause whenever
diarrhoea occurs in young calves in the region.
Table 2: MILKSA - JanvR testing of snails for Fasciola + Paramphistomidae infections
Date
Farm
Mud patch
1
5
12/12 negative
~
~
2
6
1+3
12/12 negative
~
~
~
1
6
3
3 (near dairy)
1
5+6
3
2
6
10/10 negative
1/11 positive
5/5 positive
~
8/8 negative
5/10 positive
8/12 positive
1/12 positive
~
10/10
negative
~
1/1 negative
1/1 negative
3/3 negative
~
6/6 negative
~
~
~
L. tr: Paramphistomid(?): 1
L.tr: Paramphistomid(?): 5
~
~
L tr: Fasciola(?): 1/ + Paramphistomid(?):1
L.tr: Paramphistomid(?): 8
L.tr: Fasciola(?): 1
4
1
2
4
1
2
4
4
5
3
6
5
3
3+6
5+6
~
~
4/10 positive
2/10 positive
6/10 positive
1/6 positive
1/20 positive
3/80 positive
2/120 positive
5/5 negative
4/4 negative
~
~
~
~
~
~
~
~
~
Fasciola(?): 2 / + Paramphistomid(?): 2
L.tr: Paramphistomid(?)
L.tr: Paramphistomid(?)
L.tr: Paramphistomid(?)
L.tr: Paramphistomid(?)
L.tr: Paramphistomid(?)
L.tr: Paramphistomid(?):1/+Ornithobil(?):1
No samples
1
~
3
Aug - 2015
L. truncatula L. columella
4
Sep - 2015
1
2
4
Oct - 2015
Nov - 2015
Dec - 2015
Jan - 2016
Feb - 2016
~
~
~
10/10
negative
Trematode genera
~
~
*NB - immaterial of the sort of parasite, it shows the presence of trematode parasite eggs in the snail mud patches
Paramph.(?)-Black rediae // Fasciola - white rediae (identifications to be confirmed, but samples were taken to this end)
Collection of samples: All Fasciola(?) and only some of the Paramphistomid(?) samples taken for later identification
The small numbers of snails evaluated in the laboratory militate against any firm conclusions on
seasonal cycling of the worm infection in the intermediate hosts. Nevertheless, the results are
valuable in relation to confirmation of the susceptibility of the various snail species recovered to the
two types of trematodes, and, if possible, the snail identifications are to be done as and when the
necessary funds may become available after essential running costs of the project have been
covered.
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 local
on-farm effects such as the length of time any given camp has remained ungrazed before being
sampled for snail recovery. In other words, because the sampling has occurred over only 9 months
of the year, 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
practically no L. truncatula snails (the principal intermediate host of F. hepatica) and only a handful
of L. columella having been recovered from Farm III over the total of nine sampling occasions.