Agriculture Reference
In-Depth Information
production does not always refl ect the number of worms
present (depends on the species); eggs cannot be com-
pletely identifi ed by species and are grouped in various
categories; how long infection has persisted; level of host
immunity; fecal consistency (solid-diarrhea); and some
methodologies used for EPG determination may be less
precise than others. The FEC can serve as an indicator of
seasonal changes in level of infection.
It is important to note that if heavy infection occurs over
a short period of time (1-2 weeks) with
H. contortus
,
animals may lose substantial amounts of blood without
having very many eggs in the feces because late-stage
larvae also are blood feeders.
The two common methods for determining FEC are the
McMaster and centrifugation fl otation methods. Details for
these procedures can be found in goat health handbooks.
effective tool for identifying those animals that require
treatment. It has been shown that a majority of the animals
may not require treatment based on FAMACHA scores
(van Wyk and Bath, 2002).
Worm Count and Identifi cation
The most absolute and direct method for documenting the
number of worms present in an animal is to perform a
necropsy and collect, identify, and count the worms
present. This should be done by a properly trained veteri-
narian or other professional, and it might be very expen-
sive. One can get an idea of the magnitude of
H. contortus
infection by looking for the worms that are visible on the
abomasal mucosa. It should be noted that the longer the
animal has been dead, the more the worms will move down
the gut and won't be seen, thus giving the false impression
that worms were not the problem. It is important to also
note that
Telodorsagia
and
Trichostrongylus
are too small
to see except under a microscope.
Blood Packed Cell Volume (PCV)
Nematode parasites can affect an animal's ability to main-
tain erythropoiesis (making red blood cells). The PCV is
the percent of the blood that is red blood cells, and normal
blood is usually above 30%. When PCV drops below 20%,
symptoms of anemia (lethargy, anorexia, etc.) usually start
to appear.
Haemonchus contortus
is the primary nematode
parasite that causes anemia and can lead to substantial
acute blood loss and death. Anemia is used to support
other infection response criteria, and is not necessarily a
“ stand - alone ” diagnostic tool. The most common method
for determining PCV is the use of a microhematocrit
centrifuge.
DEWORMERS (ANTHELMINTICS)
Dewormers are chemicals (drugs) that have been evaluated
and tested (for effectiveness and safety) for use in animals
to remove worms. For the most part, pharmaceutical com-
panies will not market a dewormer unless it is essentially
100% effective. As long as dewormers remain effective,
control is relatively easy and cost effective. However,
worms have developed resistance to almost all dewormers
(Howell et al., 2008). Therefore, reliance on dewormers
has become limited. Only FDA-approved dewormers can
be used legally without restrictions in the U.S. Non-
approved dewormers can be used “ extra - label ” (i.e., using
a product other than for which it is approved) and are
subject to specifi c regulations as delineated by the FDA.
The veterinarian has to have contact with the animals and
make a diagnosis that the parasite situation is potentially
life threatening. The veterinarian has to establish that none
of the approved dewormers will work (i.e., FEC reduction
or Drenchrite® testing). Once the approved dewormers
have been tested and shown not to be effective, then other
dewormers can be used “extra label.”
Anemia and FAMACHA
Level of anemia can be roughly evaluated by observing
the color of mucous-membrane areas fi lled with capillaries
close to the surface so that tissue color refl ects blood
color. Such areas are inside the lower eyelid, the gums
(only where pigmentation is not present), and inside the
vulva.
The FAMACHA eye color chart system was developed
in South Africa (Bath et al., 1996; van Wyk and Bath,
2002) to help producers monitor and evaluate level of
anemia without having to rely on laboratory testing. In this
method, the lower eyelid mucous membranes are exam-
ined and compared to a laminated chart showing fi ve
colors that represent different levels of anemia: 1 (red,
non - anemic); 2 (red - pink, non - anemic); 3 (pink, mild -
anemic); 4 (pink-white, anemic); 5 (white, severely
anemic). Since anemia is the primary pathologic effect
from infection with
H. contortus,
this system can be an
Dewormer Classes
The three general classes of dewormers available in the
U.S. are benzimidazoles, imidazothiazoles, and macrocy-
clic lactones. The more commonly used benzimidazole
dewormers are fenbendazole (Safeguard, Panacur) and
albendazole (Valbazen). Imidazothiazole dewormers are
levamisole (Levisol, Tramisol) and morantel tartrate
