Everett E. Lund

Reciprocal Responses of Eight Species of Galliform Birds and Three Parasites: Heterakis gallinarum, Histomonas meleagridis, and Parahistomonas wenrichi

Embryonated eggs of Heterakis gallinarum from chickens and turkeys, carrying both Histomonas meleagridis of relatively low virulence and Parahistomonas wenrichi, were fed to 8 species of galliform birds. Heterakis developed best in young ring-necked pheasants, with young guinea fowl next best, and then young New Hampshire chickens. No mature heterakids were recovered from young chukar partridges and young turkeys or mature Japanese quail and bobwhites. In year-old Hungarian partridges a few female heterakids matured, but yielded only 8 embryonated eggs per 100, such eggs given. Histomonas meleagridis was detected in only 1 of 8 (12%) of each of the following: mature Japanese quail, bobwhites, Hungarian partridges and ring-necked pheasants, and infections were of short duration. Fifty percent of the guinea fowl and chickens, 62% of the turkeys, and 88% of the chukar partridges became infected. There was no mortality. Only the pheasants and chickens produced worms with eggs that transmitted Histomonas to susceptible turkey poults. P. wenrichi appeared in only guinea fowl, chickens, pheasants and turkeys, and usually only when Histomonas was absent or no longer in the tissues. During the past 18 years, more than 40 experiments conducted at this Laboratory have compared the responses of various species of galliform birds to one or more of the parasites associated with histomonad infections: Histomonas meleagridis (Smith, 1895) Tyzzer, 1920; Heterakis gallinarum (Schrank, 1788) Madsen, 1949; and Parahistomonas wenrichi (Lund, 1963) Honigberg and Kuldova, 1969. These comparisons, made with hosts given the same inoculum, usually included the responses of 5to 8-week-old New Hampshire chickens and Beltsville Small White turkeys (Lund and Ellis, 1967; Lund, 1967b; Lund and Chute, 1970, 1971a, b, 1972). Almost always, the size of the infective dose was governed by knowledge of the influence of three factors: the strain of parasite to be used, its adaptation to a particular host species (Lund et al., 1970), and the host species to be inoculated; this knowledge was obtained by pretesting the infective material. However, all three parasites were not studied in each experiment, and the influencing factors mentioned above were not uniform throughout. The present study employed for the first time the same inoculum for gallinaceous birds of eight species, with uniform methods throughout for studying responses of all eight hosts Received for publication 3 March 1972. and all three parasites, including the ability f the parasites to perpetuate their kind. MATERIALS AND METHODS

Immunizing action of in vitro-attenuated Histomonas meleagridis in chickens and turkeys☆

Abstract Histomonas meleagridis was cultivated more than 6 years in Tissue Culture Medium 199, fortified with serum and antibiotic-killed bacteria of cecal origin. The histomonads first lost their ability to produce disease but retained some immunizing ability. During the sixth year of in vitro cultivation, representing serial passages 730–835, the immunizing ability declined. At the same time, these attenuated histomonads were also losing their ability to survive in the presence of freshly isolated, antibiotic-killed cecal bacteria. Meantime, freshly isolated histomonads were unable to live in the culture medium with only the limited flora that had survived the numerous in vitro passages. Apparently, long continued cultivation operated selectively on both the bacteria and Histomonas, leaving only histomonads with no ability to penetrate the hosts tissues.

Infectivity of Heterakis gallinae eggs with Histomonas meleagridis.

Abstract 1. 1. In tests herein reported, fewer than one of every 200 embryonated eggs of the cecal worm, Heterakis gallinae , were found to contain the blackhead parasite, Histomonas meleagridis . This was determined by orally administering to chickens 6 weeks of age known numbers of cecal worm eggs which had been embryonated under laboratory conditions. 2. 2. The observed rate of infectivity of the cecal worm eggs as regards Histomonas was approximately the same in eggs recovered from a succeeding generation of the worms, as determined by inoculation of susceptible birds with such eggs. 3. 3. The number of Heterakis eggs containing Histomonas was not the same for all cecal worms. More than half of the worms contained no eggs with Histomonas , and worms which did contain such eggs averaged only two each. 4. 4. These tests were conducted with a naturally-occuring, nonpathogenic strain of Histomonas . The situations herein described are not necessarily entirely comparable to those which exist with pathogenic strains.

Relative importance of young and mature turkeys and chickens in contaminating soil with Histomonas-bearing Heterakis eggs.

Young chickens were 16 times as important as mature chickens in contaminating soil with Histomonas-bearing Heterakis eggs. Young turkeys, however, produced so few such eggs as to be of no importance. Mature turkeys were nearly as important as young chickens in contaminating soil with Heterakis eggs capable of transmitting. Histomonas, but the histomonads they transmitted did not produce as severe a form of disease.

Performance in Chickens and Turkeys of Chicken-Adapted Heterakis gallinarum

1. Helerakis gallinarum recovered from chickens, and apparently having lived exclusively or predominantly in chickens for several years, thrived better in chickens than in turkeys, when several hundred embryonated eggs were given in a single feeding. 2. Use of a smaller inoculum reduced the difference in the worms performance in its traditional host and the new host species. 3. Performance in both species of host was the same following the feeding of small numbers of eggs from worms grown 1 generation in turkeys.

Means of acquisition of Histomonas meleagridis by eggs of Heterakis gallinarum

Experimentally we have demonstrated what Lee (1969, 1971 a, b) postulated on the basis of morphological considerations. The female heterakid is capable of transmitting H. meleagridis from the bird to the caecal worm egg without the intervention of the male except for fertilization. If the male is otherwise involved in the transmission of H. meleagridis , it seems unlikely that its role is of appreciable significance in the life-cycle of the histomonad as we know it now. However, if as believed by many, the histomonad was originally a parasite of a nematode that may not have been an obligatory parasite, the role of the male worm may have been considerably more important to the survival of the histomonad.

Heterakis AND Histomonas INFECTIONS IN YOUNG PEAFOWL, COMPARED TO SUCH INFECTIONS IN PHEASANTS, CHICKENS, AND TURKEYS

Young peafowl (Pavo cristatits), when tested for susceptibility to histomoni-asis by feeding embryonated eggs of Heterakis gallinarum carrying Histomonas meleagridis, were almost as susceptible to the disease as young Beltsville Small White turkeys. The disease developed more slowly, but, by 14 days after inoculation morbidity was 100% and 84% died. The young peafowl is so much more susceptible to histomoniasis than either chickens or pheasants that it should never be permitted to mingle with these birds, except where earthworms, the means of transmission of Heterakis, are absent. However, the young peafowl is unimportant in transmitting Histomonas meleagridis because the cecal worm rarely completes its life cycle in a young bird of this species when histomoniasis is present.

Bobwhite, Colinus virginianus, as Host for Heterakis and Histomonas

Bobwhites were experimentally infected with Histomonas meleagridis and Heterakis gallinarum. Chickens and turkeys were similarly infected for comparison. Although the bobwhites were nearly as susceptible to Histomonas infections as were New Hampshire chickens, and more susceptible to tissue invasion, clinical histomoniasis was much less severe than in young turkeys. The bobwhites were poor hosts for Heterakis, whether Histomonas was also present or not. Thus, it appears that bob-whites are relatively unimportant in contaminating soil with Histomonas-bearing Heterakis eggs.

Transfer of ten-day Heterakis gallinarum larvae: Effect on retention and development of the heterakids, and liberation of Histomonas and Parahistomonas

Abstract Transfer of 10-day Heterakis gallinarum larvae from donor chickens to recipient chickens and turkeys resulted in an abrupt loss of approximately half of the transferred worms. However, worms of both sexes surviving to maturity in recipient chickens were larger than in either the recipient turkeys or the control chickens in which the heterakids were allowed to develop undisturbed. Also, female worms recovered from recipient chickens contained substantially more eggs that embryonated than did females recovered from recipient turkeys or control chickens. Histomonas meleagridis was found in the cecal droppings of some recipient birds only 3 days after the larvae were transferred, and the incidence of infection rose rapidly thereafter. The nonpathogenic histomonad, Parahistomonas wenrichi, was also found frequently in recipient birds. A positive correlation was observed between the number of heterakids lost per bird and the incidence of Histomonas infections, suggesting that liberation of histomonads often occurs as the heterakids die. It was also found that far more heterakids carry histomonads than liberate them during the normal course of the life cycle. These findings are important in formulating chemical or biological control programs.

Potential of young and mature guinea fowl in contaminating soil with Histomonas-bearing Heterakid eggs.

SUMMARY Six-week-old and mature guinea fowl were tested for their ability to withstand histomoniasis, and their potential for voiding Histomonas-carrying eggs of Heterakis gallinarum, thus becoming a source of infection for other galliform birds. Guinea fowl of both ages were as susceptible to infection with Histomonas meleagridis transmitted by eggs of Heterakis gallinarum as were either chickens or turkeys, though the infections were limited to the ceca. There were no deaths and almost no morbidity among the guinea fowl. Young guinea fowl produced almost twice as many mature female heterakids as did adult guinea fowl, but slightly fewer such worms than the young chickens produced. The respective numbers of heterakid eggs that embryonated for young guinea fowl, mature guinea fowl, and chickens were in the ratio of 3:2:3. However, the eggs from worms recovered from the chickens transmitted Histomonas to susceptible poults so frequently that the young chickens would have contaminated soil 1?/ times as heavily as would the guinea fowl of either age. Young turkeys were ineffectual in producing Heterakis eggs capable of transmitting Histomonas.