Order. Hæmosporidia, Danilewsky emend. Schaudinn.
The Hæmosporidia are a group of blood parasites, comprising forms differing greatly among themselves. Some of the forms need much further investigation. However, there are certain true Hæmosporidia which present close affinities with the Coccidia, leading Doflein to use the term Coccidiomorpha for the two orders conjoined.
The Hæmosporidia present the following general characteristics:—
(1) They are parasites of either red or white blood corpuscles of vertebrates during one period of their life-history.
(2) They exhibit alternation of generations—asexual phases or schizogony alternating with sexual phases or sporogony—as do the Coccidia.
(3) There is also an alternation of hosts in those cases which have so far been completely investigated. The schizogony occurs in the blood or internal organs of some vertebrates while the sporogony occurs in an invertebrate, such as a blood-sucking arthropod or leech.
(4) Unlike the Coccidia, resistant spores in sporocysts are not generally produced, such protective phases in the life-cycle being unnecessary, as the Hæmosporidia are contained within either the vertebrate or invertebrate host during the whole of their life.
The Hæmosporidia may be considered for convenience under five main types:—
(1) The Plasmodium or Hæmamœba type. This includes the malarial parasites of man and of birds. The asexual multiplicative or schizogonic phases occur inside red blood corpuscles and are amœboid. They produce distinctive, darkish pigment termed melanin or hæmozoin. Infected blood drawn and cooled on a slide may exhibit “exflagellation” of the male gametocytes, i.e., the formation of filamentous male gametes. The invertebrate host is a mosquito. The malarial parasites of man are discussed at length on p. [155]. Similar pigmented hæmamœboid parasites have been described in antelopes, dogs, and other mammals, and even reptiles.
(2) The Halteridium type. The trophozoite stage inside the red blood corpuscle is halter-shaped. Pigment is produced, especially near the ends of the organism. The parasites occur in the blood of birds. The invertebrate host of H. columbæ of pigeons in Europe, Africa, Brazil and India, is a hippoboscid fly, belonging to the genus Lynchia.