Rafter N Ranch, Inc

Epizootic bovine abortion (EBA) Foothill Abortion

pizootic bovine abortion (EBA) is
commonly referred to as “foothill abor-
tion” because it was originally recog-
nized as an abortion disease of cattle
that occurred after summer grazing in
the foothill regions of coastal and central
California. In the early 1950s, with the
advent of calving two year old heifers, it
became a recognizable disease with
abortion rates up 50%. EBA is also is a
phenomenon of summer grazing in the
Sierra Nevada Mountains and the Great
Basin regions of California, and has been
diagnosed in southern Oregon and west-
ern Nevada.

IS A TICK TRANSMITTEDABORTION DISEASEEBA is a disease that is apparently only
transmitted by the bite of a particular
soft-bodied tick commonly known as the
pajahuello (or pajaroello) (pronounced
pa-ha-way’-lo). The scientific name of
the tick is Ornithodoros coriaceus. De-spite several decades of study, the dis-
ease agent the tick is transmitting has
eluded researchers. Suspected agents
have been isolated from aborted fetuses
and from the tick, but none has proved to
fulfill Koch’s postulates for recreating the
disease when put back into pregnant
cows. Recently, thymus from an aborted
fetus has apparently transmitted EBA to
a pregnant cow under experimental con-
ditions.

FOUR THINGS ARE NEEDEDFOR EBA TO OCCURFirst:Cattle must be six months orless in pregnancy. Experimentally,
cattle that were as early as 35 days
pregnant when exposed have
aborted Secondajahuello ticks must bepresent and hungry in the range the
cattle are utilizing. Ticks don’t re-
feed for about two months aftere x -
posure to cattle.Third:No previous exposure tothe disease means animals
have no immunity to it.I m -munity can apparently belostif exposure to the disease
has not occurred for one to
two years. Apparently, immu-
nity can only be obtained when an
animal is sexually mature (10
months or older).Fourth:Ambient tempera-tures must be warm and
dry enough to activate
the tick’s metabolism or incu-
bate the unknown agent
within the tick’s body (pos-
sibly in the 70s F.), while still
staying above freezing at night. In
coastal and central California, this
weather pattern usually occurs from
May through October. In the moun-
tains and high desert regions, the
warm months typically are June
through October. Unusually warm,
dry winters can cause EBA to occur
in normally “safe” periods.

ABORTION OCCURS 3-4MONTHS AFTER EXPOSURETO TICKIf all of the above four factors exist at the
same time, EBA abortions can be ex-pected to occur 3 to 4 months later. To
determine where disease exposure (tick
exposure) happened, the producer must
be able to identify where his cattle were
grazing 3 to 4 months prior to the onset of
abortions.

THE TICK “LIVES” IN COW ANDDEER BED GROUNDSThe existence of pajahuello ticks in a
pasture can be verified by collecting them.
The tick resides in the soil and organic
matter found in deer and cattle bedding
areas; this tick does not “quest” nor climb
up on brush like most of its hard-bodied
cousins. Few people have seen this tick
in the field. Its bite on the human is very
painful and subsequent bites cause skin
necrosis and very swollen areas.

TICKS DON’T LIVE IN WETAREAS OR PLACESTHAT FLOODDon’t bother looking in irrigated pastures
or areas that are subject to flooding. The
pajahuello doesn’t survive well when sub-
merged or damp. Look above the high
water mark when in gulches and arroyos.
They have been found in desert dry wash
creek beds.

THE TICKS ONLY STAY ONTHE COW ABOUT 20 MINUTESAT A TIMEUnlike hard-bodied ticks that attach to
their host for 7 to 10 days, the pajahuello
only requires about 20 minutes of attach-
ment in order to completely engorge itself
with blood. Once full, the tick drops off the
animal and quickly buries itself back in
the soil. The exception to this behavior is
the larval stage tick that hatches from the
egg. These very tiny creatures stay at-
tached for a week or more while they
slowly engorge and grow to several times
their original size. After the larva leaves
the animal, it molts and becomes a nymph.
Thereafter, each time a nymph feeds, it
molts and becomes a larger nymph. This
process continues through 5 to 7 nymph
stages (instars) before the tick becomes
an adult. Adult females are unmistakably
larger than adult males. Females will lay
about 300 eggs following each blood meal.
The life span of the pajahuello is un-
known, but experimentally, large females
have lived in plastic dishes for four years
without having a blood meal.