Studies of acute toxicily and anthelmintic activity of pyrethrins in sheep and rabbits
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.