Head-lice infestations and their treatment

Head-lice infestations periodically cause disruption at schools and crèches. The life cycle of the insect and the treatment of infestation are discussed. Treatment is usually relatively simple and effective, relying mainly on the use of insecticides such as gamma benzene hexachloride, malathion and pyrethrins. Appropriate therapy for problem areas, for example the eyebrows, is also described.

The avermectins: A new family of antiparasitic agents

The avermectins are macrocyclic lactones produced by fermentation of the soil micro-organism Streptomyces avermitilis. They show activity against a broad range of nematodes and arthropod parasites of domestic animals at dose rates of 300 microgram/kg or less. Unlike the macrolide or polyene antibiotics, they lack significant antibacterial or antifungal activity. By oral or parenteral administration, avermectins are active against gastrointestinal nematodes and lungworms, and important ectoparasites such as lice, mange mites, ticks and larval stages of flies. They show excellent activity against parasites resistant to existing anthelmintics or ectoparasiticides. The avermectins appear to cause paralysis of nematodes and arthropods by opening gamma-aminobutyric acid-mediated chloride channels at the neuromuscular junction.

Treatment of infestation with Phthirus pubis: comparative efficacies of synergized pyrethrins and gamma-benzene hexachloride

In recent years there has been a steady increase in the incidence of infestation with Phthirus pubis, a sexually transmitted louse. A recently introduced nonprescription liquid pediculicide, whose major ingredient is 0.3% pyrethrins synergized by 3.0% piperonyl butoxide (RiD), was compared for efficacy and safety with a prescription-only pediculicidal lotion whose major ingredient is 1% gamma-benzene hexachloride (Kwell). Thirty adult man and women with P. pubis infestation were assigned randomly to treatment with either the synergized pyrethrins or gamma-benzene hexachloride. A single 10-min application of the synergized-pyrethrin liquid produced the same results as a single 12-hr application of the gamma-benze hexachloride lotion: total eradication of adult lice and nymphs, cessation of pruritus, and no treatment-induced side effect. A follow-up visit a week after treatment verified all eradications.

ANTONY VAN LEEUWENHOEK

This is an essay about the Dutch linen-draper of the seventeenth century who made more than 500 microscopes and used them to observe the tail of an eel, the sting of a bee, the nose of a louse, the brain of a fly, the spinning apparatus of a spider, the bacteria from his own mouth, etc., and who wrote enthusiastic letters to the Royal Society of London carefully describing what he saw.

BOVINE TOLERANCE FOR MALATHION: AN EXPERIMENT IN RELATION TO A CASE REPORT

Three purebred Shorthorn cattle were tested for susceptibility to malathion toxicity. They were subjects of a case report in which symptoms had been interpreted as organophosphate poisoning following the recommended pesticidal treatment for lice. Animals were experimentally overdosed with a malathion spray at three-week intervals. Individual treatments exceeded 20 times and cumulative treatments 50 times the recommended dose. No clinical symptoms could be detected at any time during or after treatment. A depression of approximately 20-30 per cent in blood cholinesterase was the only subclinical effect of toxicity observed. Variations in body weight remained within the range expected for mature animals on a maintenance diet.

POST-TREATMENT REACTIONS IN CATTLE DURING EXTENSIVE FIELD TESTS OF SYSTEMIC ORGANOPHOSPHATE INSECTICIDES

Treatment, grub infestation, and post-treatment reaction data is given for 11,537 range-managed beef cattle, of all age classes, treated for grub and louse control with various systemic organophosphate insecticides during the period 1956 to 1964. Two cows died from perforation of the throat during administration of Trolene boluses. Of 6,858 calves, 71 showed adverse reactions with 4 dead. Of 4,679 cattle over one year of age, 3 showed adverse reactions with one death. No typical organophosphate poisoning occurred. One death resulted from a paraplegic reaction and necropsy showed spinal nerve damage of the type often associated with the presence of H. bovis grubs in the spinal canal. Seventy-three reactions, with 4 deaths, were of a bloat-salivation type, and necropsies of 3 indicated anaphylaxis, the other an extensive pharyngeal - esophageal necrosis. Reactions were directly associated with grub abundance. Other stress factors coincident to insecticide treatment, such as Bang's vaccination and dehorning, did not enhance reactions, and incipient coccidiosis did not predispose to reactions, nor did insecticide treatment increase susceptibility to coccidiosis. It is concluded that the observed adverse reactions resulted from the killing of grubs situated in the animal tissues.