Agriculture Reference
In-Depth Information
are present, worms can readily be seen on the abomasal
mucosal surface. Female worms are prolifi c egg layers and
can contaminate the forage with a very large number of
eggs. These worms thrive under hot and moist environ-
mental conditions, which are conducive for survival and
development of the free-living stages. They are found pre-
dominantly in tropical and subtropical regions of the
world; and in the U.S., these conditions prevail in the
Southeast. However, in the rest of the U.S. where similar
environmental conditions are encountered during the
summer,
H. contortus
transmission also frequently occurs.
Generally speaking,
H. contortus
transmission and
infection are at the lowest level during the winter.
Transmission and infection increase with the warmer tem-
peratures and increasing moisture during the spring and
then peak during the summer. Hypobiosis has not been
observed to occur to any great extent in the Southeast U.S.
because the life cycle can be maintained year-round, but it
does occur in more northern/western temperate (cold/dry)
regions of the U.S.
Animals infected with
H. contortus
show symptoms
associated with blood loss (anemia), which include pale
mucous membranes and bottle jaw (an accumulation of
fl uid under the chin). The greater the infection level the
more blood is lost, and eventually the animal may die.
Diarrhea may also be seen.
It thrives better under more cool and wet conditions similar
to
T. circumcincta
. This worm feeds on nutrients in mucus
and interferes with digestive function, resulting in diar-
rhea. It is called the bankrupt worm because death is
seldom the end result, and animals just become poor doers
leading to loss of production and income.
L
ONG
- N
ECKED
B
ANKRUPT
W
ORM
(
N
EMATODIRUS
SPP
.)
Nematodirus
spp. are relatively large worms (easily seen)
and are usually found in rather small numbers. If heavy
infection occurs, production and income losses will result
(similar to that of
T. colubriformis
). Eggs are large and
football shaped.
Large Intestinal Worms
N
ODULAR
W
ORM
(
O
ESOPHAGOSTOMUM
SPP
.)
Oesophagostomum
spp. are relatively large (easily seen)
worms and are usually found in rather small numbers.
These worms feed on blood and can contribute to the
overall anemia in conjunction with
H. contortus
. Although
this worm resides in the large intestine, the larvae are
found in the mucosa of both the small and large intestine
where they form nodules, thus the name nodular worm.
Larvae leave these nodules and migrate to the large intes-
tine where they become adults.
B
ROWN
OR
M
IDDLE
S
TOMACH
W
ORM
(
T
ELODORSAGIA
[
O
STERTAGIA
])
The other abomasal (
circumcincta
) worm of importance is
Telodorsagia circumcincta
, which is smaller than
H. con-
tortus
. These worms feed mostly on nutrients in mucous
and do not feed on blood, per se, but can ingest blood if
present. Female worms do not produce as many eggs as
H.
contortus
. Infection causes direct damage to the abomasal
mucosa thereby interfering with digestion and appetite.
Infection is usually considered a production disease
because animals do not grow very well, but death can
occur under very high infection conditions. The primary
sign of infection is diarrhea and sometimes bottle jaw. This
worm thrives in cooler wet environmental conditions,
which are encountered in the more temperate regions.
Hypobiosis occurs when environmental conditions are too
cold (winter) or too dry (summer).
W
HIPWORM
(
T
RICHURIS
SPP
.)
Trichuris
spp. are usually found in small numbers. The
posterior end of the worm is rather large and can readily
be seen. The anterior end of the worm is thread like, thus
the name whipworm. These worms are also blood feeders
and, like
Oesophagostomum
, contribute to the overall
blood loss. Female worms produce characteristic football-
shaped eggs with protruding plugs at each end.
DIAGNOSTIC METHODS
Parasitized animals can show many signs of infection
depending on the parasites present. The general signs
include rough hair coat, diarrhea, depression, weight loss
(or reduced weight gain), bottle jaw, and anorexia (off
feed). Laboratory diagnostic fi ndings may include anemia,
increased fecal egg count (FEC), and loss of plasma
protein.
Fecal Egg Count ( FEC )
FEC is used to evaluate infection level and is reported as
the number of eggs per gram (EPG) of feces. While this is
the best method for use with live animals, there are some
diffi culties associated with measurement including egg
Small Intestinal Worms
B
ANKRUPT
W
ORM
(
T
RICHOSTRONGYLUS
C
OLUBRIFORMIS
)
Trichostrongylus colubriformis
is a very small threadlike
worm and is the most predominant small intestinal worm.
