Volume 22 • Issue 02 • 2018
of faecal egg counts and 75% reduction of worm
burdens in vaccination trials (Newton & Munn
1999). The protection is closely correlated with
systemic IgG titres to H11 (Munn et al. 1997).
H11 has several desirable properties. It is an
effective immunogen in young lambs (Tavernor
et al. 1992) and is effective in a range of sheep
breeds and against anthelmintic-resistant H.
contortus strains (Newton & Munn 1999).
The vaccine antigens (H11 and H-gal-GP) are
‘hidden antigens’, since the immune systems of
small stock is not normally exposed to antigens of
the luminal surface of H. contortus intestinal cells
(Smith 1993). The immunity conferred by the
vaccine does not interfere with the development
of natural immunity (Smith & Smith 1993), but
rather provides protection when the latter is
acquired (Le Jambre et al. 2008).
Characteristics of the Protective
Immunity Conferred by Vaccination with
H. Contortus Gut Membrane Proteins
Strong evide nce has been found that the
protection obtained is antibody mediated.
Antibodies from sheep protected by the vaccine
can inhibit the protease activity of both H11
and H-gal-GP in vitro (Newton & Meussen 2003;
Ekoja & Smith 2010; Le Jambre et al. 2008) and it
is assumed that this also happens in vivo.
The concept of vaccination with proteins derived
from gut membrane has also proved to be effective
in the control of haematophagous arthropods
such as ticks. A critical internal component of the
parasite, such as a molecule on the gut cell surface,
is first isolated and then used to vaccinate the
host. In an ectoparasite feeding on blood or tissue
fluid and wound exudate, subsequent uptake of
blood or other fluid containing antibodies from
the host that is accompanied by, for example
complement and cells, can lead to immunological
damage to the host. This approach is the basis of
the B. microplus vaccine (Willadsen 1999).
Following vaccination, an antibody response
involving high-titre circulation is raised.
Antibodies are ingested with the blood during
the feeding of the helminths and bind to
functional proteins on the brush border of
intestinal cells, which compromises digestion.
This eventually leads to starvation, loss of
fecundity and weakness. Finally,
the helminths detach and are
expelled (Smith & Zarlega 2006).
Vaccine-induced immunity can be
passively transferred by serum or
colostrum (Smith 1993, Andrews
et al. 1997). It has been shown
that serum antibody titres are
highly correlated with protection
(Le Jambre et al. 2008).
Specificity of the Vaccine
This H. contortus antigen vaccine is genus
specific. It is ineffective against Teladorsagia
circumcincta, Trichostrongylus axei and Cooperia
oncophora (Smith et al. 2001), but protects
calves against H. placei (Basseto et al. 2011).
The antigens H11 and H-gal-GP of H.contortus,
derived from gut membrane, appear to be highly
conserved. Antigens harvested from H.contortus
in any part of the world are globally effective
against H. contortus challenge (Smith et al. 2001;
Munn et al. 1993; Souza et al. 2011). An efficacy
trial proved the efficacy of the H-gal-GP antigen
complex against the anthelmintic-resistant South
African White River strain of H. contortus (Smith
2007; Smith & Smith 1993).
Results and Indications
Effective vaccination would be an alternative
control measure to address haemonchosis
in small stock and to limit the reliance on
anthelmintics. The additional benefit would be
to slow down the development of anthelmintic
resistance and to enable the small stock farming
industry in South Africa to remain productive
and competitive.
It is recommended that vaccination starts 9
weeks prior to the Haemonchus season. Three
injections 3 to 4 weeks apart are needed to
induce protection, after that, immunity can be
maintained by boosters given at 6 to 8 week
intervals until the first frost lowers infection rate.
It is of utmost importance to ensure primary
immunisation is in place either before the
challenge starts or to minimize or lower infection
using an effective anthelmintic during this phase,
a faecal egg count of less than or equal to 1000
eggs per gram is acceptable. The
effect of peri parturient relaxation
of resistance in pregnant ewes
should be taken into account and
it is therefore recommended to
ensure immunity is in place
at least 3 weeks before the
lambing season starts.
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