Induction of immunological tolerance in rats to Nippostrongylus brasiliensis infection

A successful attempt was made to induce immunological tolerance to N. brasiliensis in laboratory rats by exposing them to larval infections before the age of immunological maturity.

The adult capacity of rats to eliminate a primary infection in 3 weeks and to acquire resistance to reinfection was developed by 5 weeks of age. On the other hand, primary infections of 250–660 larvae, originating before 4 weeks of age, survived in 61 of 83 rats up to 10 weeks. These rats were not resistant to challenge at 5 or 7 weeks of age, nor did the challenge infection undergo immune elimination. Such tolerance was evident even in rats whose primary worm burden was chemically abbreviated prior to challenge.

It was not always possible to distinguish between tolerant and immune animals on the basis of egg output patterns. Suppression of egg output occurred even in tolerant rats harbouring relatively stable female populations.

For immunological experiments on N. brasiliensis infection in rats, the determination of a ‘take ratio’ is advocated: (20 day take/10 day take) × 100. This ratio eliminates the error inherent in variability of takes and renders comparable the results of different experiments.

The work was carried out in 1965 during tenure by one of us (T.K.) of an Exchange Scholarship under the British–Hungarian Cultural Agreement. Supervision by Professor W. Mulligan and the co-operation of colleagues in the Wellcome Laboratories are gratefully acknowledged.

Control of some internal parasites of chinchillas

An unidentified coccidia was found in chinchillas. Treatment with sulfamethazine apparently eradicated the infection from several herds. Ostertagia females and 1 Trichostrongylus colubriformis male were also found in chinchillas, causing emaciation. A dose of thiabendazole of 100 mg./kg. of body weight was effective against the roundworms, but it was toxic. A dose of trichlorphon, 100 mg./kg. of body weight, was effective and safe. Hymenolepis infection caused emaciation and death. Treatment with doses of niclosamide, 200 mg./kg. of body weight, was successful in removing tapeworms, ending deaths, and improving the condition of the host. It did not eradicate the infection.