| dc.description.abstract | Pyrethrins are natural insecticides extracted from the
dried flowers of Chrysanthemum cinerariaeJolium plant. They
are considered to be the safest of the insecticides available.
Although they are widely used on farm animals for control of
external parasites and many trials have been done in relation
to their use in the control endoparasites, there is no
information on toxicity of pyrethrins in farm animals. Acute
toxicity studies of pyrethrins in laboratory animals have been
reported, but similar studies have not been done in sheep and
information on treatment of pyrethrin toxicity in farm animals
is very scanty. If pyrethrins have to increasingly continue
being used in .th.efarm, veterinarians should have some idea
on their toxicity in farm animals and how such toxicities can
be treated. The main objective of the present study was to
. evaluate the acute toxicity of pyrethrins in sheep and rabbits.
The second objective was to investigate in vitro and in vivo
effects of pyrethrins on Haemonchus contortus. The final
objective was to evaluate the effectiveness of diazepam and
pentobarbitone sodium in treatment of pyrethrin induced
poisoning in rabbits.
Fourteen adult female red masat sheep and fourty adult
newzealand white rabbits were used. The sheep were
purchased from a farmer in Kiserian and the rabbits were
obtained from Ngong veterinary farm in KaJiado district.
The oral LD50S and their 95% confidence intervals in
rabbits were 1,300 (630 to 2,521) mg/kg and 1,500 0,008
to 2.268) mg/kg b.wt for pyrethrins with piperonyl butoxide
and pyrethrins alone respectively. Rabbits previously trealed
with phenobarbitone sodium, an enzyme inducer, were very
resistant to pyrethrin poisoning. The oral LD50 was greater
than 4,500 mg/kg b.wt. The oral LD50 for pyrethrins with
piperonyl butoxide in sheep was 600 mg/kg b.wt.
The clinical signs of acute pyrethrins toxicity observed
after oral administration in sheep and rabbits were
hyperexcitation, tremors, convulsions, paralysis and death.
At postmortem there was extensive pulmonary
congestion and oedema and ecchymotic haemorrhages in
respiratory and cardiovascular systems. Death was probably
due to failure of respiratory and cardiovascular systems in
both species.
Haematological and biochemical parameters were
evaluated in a control and two treatment groups of sheep
using routine laboratory procedures. Administration of
pyrethrins orally at 210 mg/kg did not affect haematologtcal
parameters in sheep. However, administration of pyrethrins at
420 mg/kg caused a significant decrease in white blood cell
counts (WBC), red blood cell counts (RBC) and neutrophils
and an increase in packed cell volume and lymphocytes
(p<0.05). Eosinophils, haemoglobin concentration and mean
corpuscular haemoglobin concentration were not affected by
pyrethrins in sheep (p>O.05).
Administration of pyrethrins orally at 210 and 420
mg/kg did not cause any significant effects on the following
-xvllibiochemical
parameters assayed in serum; a sp a rt a te
aminotranferase, glutamate dehydrogenase, creatinine and
total proteins (p>0.05). However pyrethrins caused a
significant rise in sorbitol dehydrogenase (p< 0.05). The
mean serum levels of sorbitol dehydrogenase were 288 for
the control, 412 in the group that had received 210 mg/kg
b.wt and 473 sigma units for the group that received 420
mg/kg b.wt pyrethrtris.
Externally pyrethrins caused slight to moderate ocular
irritation in sheep characterised by hyperaemia of
conjunctiva, chemosis and lacrimation. On the skin,
pyrethrins caused moderate irritation characterised by
erythema and oedema.
Trials on the effects of pyrethrins on Haemonchus
contortus indicated that pyrethrins were lethal to the adult
worms and their larvae in vitro, were not ovicidal and did not
affect faecal egg counts when administered orally at a dose of
168 mg/kg b.wt.
Pyrethrins alone and with the synergist piperonyl
butoxide were slightly toxic to both sheep and rabbits, while
pyrethrins alone after prior treatment with phenobarbitone
sodium, an enzyme inducer were practically non toxic to
rabbits.
Although there were some effects on some
haernatologtcal and biochemical parameters, these effects
were not significant in terms of range of values or in overall
pattern. Pyrethrins administered orally were not lethal to the
worms in vivo and this can be explained as being due to rapid
decomposition of pyrethrins in the gastrointestinal tract.
It was concluded that pyrethrins have potential
anthelmintic activity in farm animals. Acute pyrethrins toxicity
can be treated with pentobarbitone sodium and diazepam.
These studies indicate that pyrethrins are mild irritants of the
skin and eyes and are slightly toxic to mammals. | en |
