Protective heterologous immunity between Plasmodium atheruri and other Plasmodium spp. and Babesia spp. in mice

Mice which have recovered from infections with P. atheruri are immune to challenge with the homologous parasite and are also strongly resistant to challenge with P. v. chabaudi and, to a lesser extent, B. rodhaini, B. microti and P. b. yoelii. There is little protection against P. v. vinckei and none against P. b. berghei. In the reciprocal experiments, the greatest degree of protection against P. atheruri occurs after P. v. chahaudi infections but over two-thirds of mice are protected by B. rodhaini or B. microti, half by P. v. vinckei or P. b. berghei but hardly any by P. b. yoelii. The considerable degree of cross-protection which exists between P. atheruri and P. chabaudi can be correlated with some antigenic similarities between these parasites but these are not greater than those of parasites which do not protect against one another.

Absence of immunity between Trypanosoma musculi and intra-erythrocytic protozoa in mice

Mice which have recovered from, infections with Trypanosoma musculi exhibit no immunity to challenge with the malaria parasites, Plasmodium v. vinckei, P. v. chabaudi, P. b. berghei, P. b. yoelii or P. atheruri, the piroplasms Babesia rodhaini or B. microti or the dactylosomid Anihemosoma garnhami. Recovery from infections with any one of these parasites confers no immunity against T. musculi. These results indicate that heterologous immunity between intra-erythrocytic protozoa does not extend to trypanosomes.

Immunity to malaria and piroplasmosis in mice following low level infections with Anthemosoma garnhami (Piroplasmea: Dactylosomidae)

Mice which have recovered from infections with A. garnhami do not succumb to; challenge with the piroplasms B. rodhaini or B. microti and over half such animals are protected against the malaria parasites P. v. vinckei and P. v. chabaudi. This protection does not extend to the malaria parasites P. b. berghei or P. b. yoelii. Mice which have recovered from infections with the piroplasms are protected against A. garnhami, as are those which have recovered from infections with P. v. vinckei or P. v. chabaudi. About half the mice which have recovered from infections with P. b. berghei or P. b. yoelii are also protected against A. garnhami. This interaction between intra-erythrocytic protozoa may influence the incidence of these parasites in the wild. A. garnhami is unlikely to be of any use in the immunization of humans against malaria but could be of use in the protection of cattle against piroplasmosis.

Nuttallia meri sp.nov.--a new piroplasm from Psammomys obesus in the lower Jordan Valley

A piroplasm was isolated from a wild-caught Psammomys obesus from the lower Jordan Valley. In wild-caught Psammomys the infection is submicroscopic or of very low intensity, but rises sharply following splenectomy. The animal from which the piroplasm was isolated died with a 44 % parasitaemia and haemoglobinuria, following splenectomy.

The piroplasm was transmissible to clean, laboratory-bred Psammomys, to hamsters and Meriones. It was not transmissible to, or gave rise only to transient infections in, adult mice, rats, Mastomys, Acomys and Arvicanthis. Suckling mice and rats showed low parasitaemias for a few days, although division forms of the parasite were observed.

No protective cross-immunity with Nuttallia danii was observed.

On the basis of its measurements, spectrum of infectivity to experimental animals and absence of cross-immunity with N. danii, the piroplasm of Psammomys is considered to be a new species.

The name Nuttallia meri, sp.nov. in memory of the late Prof. Gr. G. Mer, is proposed for this piroplasm of Psammomys obesus.

I should like to express my appreciation of the excellent technical assistance provided by Mrs Miriam Sarfatti and Mr A. Bortinger, and to thank Dr Y. Schlein for his help with some of the drawings. I am particularly indebted to Dr A. Hadani of the Kimron Veterinary Institute for providing me with Meriones and testing N. meri in his laboratory.

This study was supported by the Reubin Kunin and Samuel Lunenfeld Medical Research Foundation - to which grateful acknowledgement is made.

Antigenic variation in Babesia rodhaini demonstrated by immunization with irradiated parasites

1 Populations of Babesia rodhaini were isolated which were ‘putative’ variants of a reference population.

2. They were shown to have some antigenic dissimilarity to the reference population by comparing the response of rats immunized with irradiated parasites of the reference population, to challenge with either the reference population or with the variant populations. To the homologous challenge the immunized rats were strongly resistant. After a heterologous challenge, however, for the first 3 or 4 days the immunized rats showed no resistance but thereafter rapidly controlled the infection.

3. Five ‘variation’ populations were tested and all were shown to have some antigenic dissimilarity to the reference population. Two variant populations were compared and were not found to be identical with each other. There appeared, however, to be less dissimilarity between them and any one variant and the reference population.

Mrs J. Page and her successor Miss D. Leader, gave technical assistance. I thank my colleagues for helpful criticism of the manuscript.