Family Lankesterellidae

Members of this family are heteroxenous, with 2 hosts. Schizogony, gametogony and sporogony all take place in a vertebrate host. The sporozoites enter the blood cells and are taken up by a blood-sucking invertebrate (a mite or leech). They do not develop in this host, but are transferred to the vertebrate host when the latter eats the invertebrate, or possibly by injection. In the vertebrate host, development takes place in the host cells proper. The oocysts contain no sporocysts, but have 8 or more sporozoites, the number depending on the genus. The microgametes have 2 flagella so far as is known. There are 2 genera in this family: Lankesterella, which occurs in birds and amphibia, and Schellackia, which occurs in reptiles.

Genus Lankesterella

In this genus the oocysts contain 32 or more naked sporozoites. The vectors are leeches or mites.

The type species, and the only one known for a long time, is L. minima, a parasite of the frog. However, Lainson (1959) recently showed that the genus Atoxoplasma Garnham, 1950 is a synonym of Lankesterella, enlarging the genus considerably and clearing up a question which has puzzled parasitologists for years.

The parasites now known to be sporozoites of Lankesterella are found frequently in the lymphocytes and other blood cells of wild birds. They had been thought to be Haemogregarina or Toxoplasma, but Garnham (1950) showed that they were definitely not the latter and therefore called them Atoxoplasma.

The names and accepted species of the genus are still in a highly confused state (Laird, 1959; Lainson, 1959).

Lankesterella adiei (Aragao, 1933) Lainson, 1959 (syns., L. passer is Raffaele, 1938; L. garnhami Lainson, 1959) is a common parasite of the English sparrow thruout the world. Lainson (1959) found it in all of 99 adult and 150 fledgling English sparrows in England, Manwell (1941) and Manwell et al. (1945) reported that it was common in passerine birds, and D. D. Myers (unpublished) found it commonly in English sparrows in Illinois. The sporozoites occur in the lymphocytes and monocytes, and often cause a pronounced indentation of the host cell nucleus. They are typically sausageshaped with rounded ends, stain weakly and lack a well defined periplast, so that it is often difficult to differentiate their cytoplasm from that of the host cell. Their nucleus is diffuse and granular, with a tiny karyosome. They measure 4 to 5 by 2 to 4 u according to Lainson (1959).

The life cycle of L. adiei was described (under the name L. garnhami) by Lainson (1959). Schizogony takes place in the lymphoid-macrophage cells of the spleen, bone marrow and liver. There are 2 types of schizont, one producing 10 to 30 (average 16) oval merozoites measuring 4 by 2 u, and the other producing a smaller number of larger merozoites measuring 6 by 3.5 u. Gametogony and sporogony take place in the lymphoid-macrophage cells of the liver, lungs and kidney. The microgametocytes resemble those of Eimeria and produce 60 to 100 microgametes. The macrogametes are about 14.5 u in diameter when mature and produce a large but unspecified number of sporozoites measuring about 3.6 by 1.8 u. The vector is presumably the common red mite, Dermanyssus gallinae, but Lainson was unable to prove this because he had no uninfected receptor birds.

According to Lainson (1958), Lankesterella may cause congestion and hemorrhage of the blood vessels and inflammatory foci in the liver and lungs of infected English sparrows. Manwell (1941) stated that infections seemed to spread rapidly among adult English sparrows from New York after they had been captured and kept in relatively close quarters in the laboratory. He found that the disease was not infrequently fatal, but that chronic cases also occurred. The liver and spleen were greatly enlarged and very dark in one bird which he necropsied, but there were no hematin granules in either organ. D. D. Myers (unpublished) also observed deaths from this infection in captured English sparrows in Illinois.

Lankesterella serini Lainson, 1959 was discovered in canaries when Lainson wanted to infect them with L. acliei from the English sparrow and found that they already had an infection of their own. It apparently resembles L. adiei. Nothing is known about its pathogenicity. Perhaps the "x-bodies" or "Einschlusse" which occur in the macrophages of the lungs, liver and spleen of canaries (Manwell et al., 1945) belong to this species.