Histomonas meleagridis after One Thousand in vitro Passages

Abstract

SYNOPSIS. During a 7‐year period Histomonas meleagridis survived 1000 passages in Medium 199 fortified with serum and antibiotic‐killed bacteria. The histomonads were originally isolated from a chicken's cecal dropping, and the bacteria were cultivated from the cecal contents of a normal turkey. In many respects, the histomonads remained unchanged during cultivation, but in some other respects they changed considerably, perhaps irreversibly. Morphologically, the histomonads propagated in vitro showed only slight changes. When returned to birds, they resumed the structure characteristic of lumen‐dwelling individuals of this species. However, they had long since lost their ability to produce disease in either chickens or turkeys, and organisms of the tissue‐dwelling type were rarely seen. The long‐cultivated histomonads are actually as nonpathogenic as Histomonas wenrichi, but they have none of the distinguishing morphologic characteristics of the latter. As has been reported elsewhere, H. meleagridis long maintained in the tissue culture medium has also lost much of its ability to immunize either chickens or turkeys against infection with virulent strains of this parasite. Also lost in the process of adaptation to its restricted medium has been the ability to multiply satisfactorily in vitro with the complement of bacteria normal to the ceca of the birds. However, in some instances, histomonads which have become adapted to in vitro cultivation are still able to live in birds with this diversified flora. Activity of the histomonads cultivated in vitro differed but little from that of H. meleagridis freshly isolated from birds, when both were viewed under the same conditions. Histomonads from each of the above sources multiplied most satisfactorily in their accustomed habitat, probably because of a difference in nutritional requirements.

Vaccination against histomonosis prevents a drop in egg production in layers following challenge

“…Similarly, the number of caeca from hens that were vaccinated but not challenged and that tested positive by PCR was much lower than the corresponding number from challenged or vaccinated and challenged birds. The inability of histomonads that had been propagated for a long time to grow readily in host birds was described many years ago by Lund et al (1967) and could be the result of a hindered or retarded re-adaption to the in vivo environment, again underlining the difference between attenuated and virulent histomonads.…”

High yield of parasites and prolongedin vitroculture ofHistomonas meleagridis

“…Histomonads probably feed directly on the rice powder, since many of the parasites show rice particle inclusions at microscopy (Tyzzer, 1934;Lucas & Goose, 1965) but the rice powder probably also provides food for specific bacteria that serve as food for histomonads (Tyzzer, 1934;McDougald & Reid, 1978). These bacteria are coisolated with the Histomonas strains from the caeca of turkeys or chickens and are essential for multiplication of the histomonads (Lund et al ., 1967;Berks & Neal, 1952;Lesser, 1960;Augustine & Chute, 1978). Other ingredients of Dwyer's medium are horse serum and chicken embryo extract (Dwyer, 1970).…”

“…Initially a combination of a solid and a liquid medium was attempted (Drbohlav, 1924;Tyzzer, 1936), but later completely liquid culture media were developed (DeVolt, 1943). These usually consisted of buffered saline with 5 to 10% serum (of various mammal species) and other additions, including rice powder (Tyzzer, 1934(Tyzzer, , 1936Bishop, 1938;DeVolt, 1943;Delappe 1953;McDougald & Reid, 1978), marmite (Lucas & Goose, 1965), turkey caecal bacteria (Lesser, 1960(Lesser, , 1964Lund et al ., 1967), cream (Lesser, 1963(Lesser, , 1964, granular charcoal (Ruff & Hansen, 1970;Hirsch & Hirsch, 1977) and chicken embryo extract (Dwyer, 1970;Stepkowski & Klimont, 1979). A frequently used culture medium is Medium 199 with Hank's salts, 10% heat-inactivated horse serum, 5% chicken embryo extract and 10 to 12 mg rice powder per 12.5 ml medium (Dwyer, 1970;McDougald & Reid, 1978).…”

Molecular identification and phylogenetic relationships of trichomonad isolates of galliform birds inferred from nuclear small subunit rRNA gene sequences

“…1d (Lund 1963;Honigberg and Kuldova 1969;McDougald 2003). In addition, the cellular cycle of this trichomonad remains unknown and the existence of an aflagellated form during this cycle cannot be excluded as it has been described for H. meleagridis (Lund et al 1967). Therefore, type III isolates as well as larger cells identified in the sample AL411F6 will be considered as belonging to P. wenrichi.…”

“…Two forms of H. meleagridis have been described: an aflagellated "tissue form" and a flagellated "lumen-dwelling form" possessing one anterior flagellum, which is lost during the invasion of the host's tissues (Lund et al 1967). However, the identification of this parasite in the cecal lumen of chickens, turkeys, and pheasants was confused by findings of a larger cell type equipped with four flagella, in addition to the predominant smaller uniflagellate forms corresponding to H. meleagridis (Tyzzer 1934;Wenrich 1943).…”