Walter T. Johnson (1892 to 1937): pioneer of coccidiosis research in the fowl

Abstract

Walter T. Johnson (1892 to 1937), veterinarian at Western Washington Agricultural Experiment Station (WWAES), Puyallup, Washington, USA, and subsequently poultry pathologist and professor of veterinary medicine at Oregon State University Agricultural Experiment Station (OSAES), Corvallis, Oregon, USA, made many important contributions to our understanding of the disease coccidiosis. His pioneering work included the first description of Eimeria necatrix and Eimeria praecox from the chicken and identification of four other species of Eimeria from the fowl. He demonstrated the relationship between numbers of oocysts ingested and severity of infection, and described the phenomenon of host specificity and the significance of immunity. Contrary to widespread opinion, he considered that coccidia were not involved in blackhead disease and other pathological conditions reported from the fowl. His views on control were ahead of his time and he anticipated the possibility of vaccinating birds by infecting them with live oocysts. In addition to his studies of coccidiosis, Johnson introduced a vaccine for fowlpox and ran a pullorum-testing laboratory. He produced numerous articles of an advisory nature on a diverse range of topics concerned with poultry and cattle. Much of Johnson's research was published in bulletins of the WWAES and OSAES that are not widely available and consequently have often been overlooked by the scientific community. Following his premature death, the director of OSAES claimed, “more information on the parasitic disease coccidiosis has been discovered at the Oregon Station than at almost any other place. The Oregon Station is probably the only institution in the world where six known species of coccidia of the chicken are available in pure culture” (Anonymous, 1938a). This is a claim that few institutions can match today.

Résumé

Synthèse Walter T. Johnson (1892–1937) – pionnier de la recherche sur la coccidiose des volailles

Walter T. Johnson (1892–1937), vétérinaire à la station expérimentale d'agriculture de Washington Ouest (WWAES), Puyallup, Washington, USA, et par la suite pathologiste aviaire et professeur de médecine vétérinaire à la station expérimentale d'agriculture de l'Université de l'Etat d'Oregon (OSAES), Corvallis, a apporté une contribution très importante à la compréhension de la coccidiose. On lui doit la première description de Eimeria necatrix et Eimeria praecox du le poulet et l'identification de quatre autres espèces d’Eimeria du poulet. Il a démontré la relation entre le nombre d'oocytes ingérés et la sévérité de l'infection, il a décrit le phénomène de spécificité d'hôte, et l'importance de l'immunité. Contrairement à l'opinion répandue, il a considéré que les coccidies n’étaient pas impliquées dans la maladie de la tête noire et dans d'autres pathologies de la poule. Sa manière de concevoir le contrôle était en avance sur son temps et il a anticipé la possibilité de vacciner les animaux en les infectant avec des oocytes vivants. De plus dans son étude sur la coccidiose, Johnson a introduit la vaccination contre la variole aviaire et a entrepris le testage de la pullorose. Il a écrit de nombreux articles promulguant des conseils sur une variété importante de sujets concernant les volailles et le bétail. La majorité des recherches de Johnson a été publiée dans les bulletins du WWAES et du OSAES qui ne sont pas largement diffusés et en conséquence ont été souvent oubliées par la communauté scientifique. Après sa mort prématurée, le directeur du OSAES a déclaré “c'est à la Station de l'Oregon, plus que nulle part ailleurs, que les connaissances sur la coccidiose ont été découvertes. La Station de l'Oregon est probablement la seule institution au monde où six espèces de coccidies du poulet sont disponibles en culture pure” (Anon, 1938a). Ceci est une revendication que peu d'institutions peuvent égaler aujourd'hui.

Zusammenfassung

Walter T. Johnson (1892–1937) – ein Pionier in der Erforschung der Kokzidiose beim Geflügel

Walter T. Johnson (1892–1937), Tierarzt am West- Washingtoner landwirtschaftlichen Untersuchungsamt (WWAES), Puyallup, Washington, USA, und später Geflügelpathologe und Professor für Veterinärmedizin am landwirtschaftlichen Untersuchungsamt der Staatsuniversität Oregon (OSAES), Corvallis, erbrachte viele bedeutende Beiträge für das Verständnis der Kokzidiose Seine Pionierarbeit umfasst die Erstbeschreibung von Eimeria necatrix und Eineria praecox beim Huhn sowie vier weiterer Eimeria-Spezies beim Geflügel. Er wies die Beziehungen zwischen der Anzahl der aufgenommenen Oozysten und der Schwere der Infektion nach und beschrieb das Phänomen der Wirtsspezifität und der Bedeutung der Immunität. Im Gegensatz zu der damals weit verbreiteten Meinung glaubte er, dass die Kokzidien nicht an der Schwarzkopfkrankheit oder anderern beim Geflügel beschriebenen pathologischen Erscheinungen beteiligt waren. Seine Ansichten zur Bekämpfung der Kokzidiose waren seiner Zeit weit voraus, da er die Möglichkeit der Impfung von Geflügel durch Infektion mit lebenden Oozysten vorhersah. Außer seinen Untersuchungen zur Kokzidiose entwickelte Johnson eine Vakzine gegen Geflügelpocken und betrieb ein Pullorum-Testlabor. Er verfasste zahlreiche Artikel mit beratendem Charakter über ein breites Geflügel und Rinder betreffendes Themenspektrum. Vieles von Johnsons Forschungsergebnissen wurde in den Bulletins der WWAES und OSAES publiziert, die nicht überall verfügbar sind und deshalb von der Wissenschaft Gemeinschaft der Wissenschaftler oft übersehen wurden. Nach seinem zu frühen Tod versicherte der Direktor des OSAES, “dass am Untersuchungsamt in Oregon mehr Erkenntnisse über die Parasitose Kokzidiose gewonnen worden seien als an nahezu jedem anderen Platz. Das Untersuchungsamt in Oregon sei wahrscheinlich die einzige Institution auf der Welt, wo die sechs bekannten Kokzidienspezies des Huhns in Reinkultur erhältlich seien.” (Anon, 1938a). Dies ist ein Anspruch, den heutzutage nur wenige Institutionen erfüllen können

Revision

Walter T. Johnson (1892–1937) – pionero de la investigación sobre coccidiosis en aves

Walter T. Johnson (1892–1937), veterinario de la Western Washington agricultural experiment station (WWAES), Puyallup, Washington, USA, y posteriormente patólogo de aves de producción y catedrático de medicina veterinaria de la Oregón State University agricultural experiment station (OSAES), Corvallis, contribuyó de forma importante al conocimiento de la enfermedad llamada coccidiosis. Su trabajo pionero incluyó la primera descripción de Eimeria necatrix y Eimeria praecox en el pollo y la identificación de cuatro especies más de Eimeria de aves domésticas. Demostró la relación entre el numero de ooquistes ingeridos y la gravedad de la infección, describió el fenómeno de la especificidad de huésped y el significado de la inmunidad. Contrariamente a la opinión más extendida, él consideró que los coccidios no estaban involucrados en la histomoniasis ni en otras enfermedades de las aves domésticas. Sus ideas sobre el control eran avanzadas para su tiempo y anticipó la posibilidad de vacunar aves mediante la infección con ooquistes vivos. Además de sus estudios sobre la coccidiosis, Johnson introdujo una vacuna para la viruela aviar y puso en marcha un laboratorio para realizar pruebas de Pullorum. Produjo numerosos artículos en los que daba consejos sobre diferentes temas relacionados con las aves de producción y también con los terneros. La mayoría de la investigación realizada por Johnson se publicó en boletines de la WWAES y la OSAES a los cuales no todo el mundo tiene acceso y, en consecuencia, han sido pasados por alto con frecuencia por parte de la comunidad científica. Tras su muerte prematura, el director de OSAES reivindicó que, “mucha de la información sobre la enfermedad parasitaria conocida como coccidiosis ha sido descubierta en la Oregon Station más que en cualquier otro lugar. La Oregon Station es probablemente la única institución en el mundo donde seis especies conocidas de coccidios del pollo se encuentran disponibles en cultivo puro” (Anon, 1938a). Esta es una reivindicación que pocas instituciones pueden igualar actualmente.

Introduction

Walter Johnson was one of the pioneers of coccidiosis research in the fowl. A year after his death on 29 December 1937, Oregon State University Agricultural Experiment Station (OSAES) produced a bulletin with a series of plates depicting oocysts of six then known species of Eimeria in the chicken (Johnson, 1938). The plates, together with exceptional drawings of life cycle stages by his contemporary, Edward E. Tyzzer (Tyzzer, 1929; Tyzzer et al., 1932), are among the finest illustrations of the Eimeria parasite that have been produced. Although published in his name, the bulletin was actually compiled by his wife from rough manuscript notes and tables prepared by her husband over a period of research that occupied later years of his life. The bulletin is illustrated with detailed drawings of chicken cages, a portable table, surgical instruments, and a floor plan of the poultry house (designed by Johnson), to “eliminate contamination as far as possible and yet approximately provide normal rearing conditions” (Johnson, 1938). The equipment also included a large tank for steam-cleaning cages, and was constructed by Johnson with the help of one assistant (A. S. Rosenwald, personal communication, 2003). Much of Johnson's work was published in such bulletins and has not been quoted widely in the scientific literature. In a recent review of the origins of coccidiosis research in the fowl, some of his contributions to this field were outlined (Chapman, 2003). In this article, Johnson's research is described in greater detail, biographical information is presented, and the significance of his many valuable contributions to our knowledge of coccidiosis is discussed. The principal literature source was the Experiment Station Records of the US Department of Agriculture (Office of Experiment Stations, Washington) from 1918 to 1938. The references cited are believed to comprise all of Johnson's publications.

Vitae

Walter Johnson was born at Tower, Minnesota on 2 March 1892 but moved at an early age to western Washington, Washington state. His personal file records that he was raised part of the time on a small farm and then gained about 2 years’ experience working as a farm hand with general livestock. He studied at Washington State College in Spokane from 1911 to 1917, receiving a B.S. degree in agriculture in 1915 and taking dairy husbandry and veterinary medicine as major subjects. He received a degree in veterinary medicine from the College in 1917, and from 1917 to 1919 was employed as an instructor in veterinary medicine. He then accepted the position of veterinarian for Western Washington Agricultural Experiment Station (WWAES) (for which a biennial appropriation of $10 000 had been set aside by the state legislature). In August 1925 Johnson was appointed poultry pathologist at OSAES, with an initial stipend of $3000, and subsequently was promoted to the rank of Professor of Veterinary Medicine. In addition to acting in an advisory capacity to poultry breeders of Oregon he taught two courses, diseases of poultry and anatomy of the fowl (Oregon State Barometer, 13 October 1925). He was a speaker on Monday night programs of radio KOAC, a broadcasting station run by the College, and lectured on poultry diseases and parasitology (Anonymous, 1926a). At the time of his death, the Oregon State College notice of appointment indicates that his service distribution was 18% instruction, 67% experiment station, and 15% agriculture technical advisory service, for which he was paid $4200. He joined the American Veterinary Medical Association (AVMA) in 1924 and was a member of Washington State Medical Association, the American Association of Instructors and Investigators in Poultry Husbandry, and several university fraternities. A. S. Rosenwald, at one time assistant poultry pathologist at OSAES, met Johnson during the last 8 months of his life. He recollects that he was an energetic, inventive man, a loner who worked entirely on his own with little technical help, that he was a clear speaker, and that he spoke very highly of his contemporary, Edward E. Tyzzer. A rare photograph of Johnson survives (Figure 1). A group photograph that includes Johnson, one of the “Corvallis Veterinary Octette”, was taken at the 67th AVMA meeting held in Los Angeles in 1930 and published in the journal (Anonymous, 1930a).

Figure 1. Photograph of Johnson reproduced from KOAC Radio Programs, 1925/1926 (Anonymous, 1926a).

Research at WWAES

While at WWAES Johnson wrote two papers for Poultry Science concerned with host specificity, transmission, control, and diagnosis of coccidiosis in the fowl (Johnson, 1923a,1923/1924). The 1923/1924 paper was prepared especially for Poultry Science following requests to the editor for more information on poultry diseases. The 1923 paper was reprinted in The North American Veterinarian (Johnson, 1923b). He also wrote numerous articles for the monthly bulletin of WWAES that covered diverse topics such as anatomy of the fowl, postmortem techniques, surgical procedures, causes of mortality, poultry disease management, and prevention. He provided descriptions of many poultry diseases and pathological conditions including nasal catarrh, roup, chickenpox, contagious white diarrhoea, tuberculosis, botulism, helminth and lice infections, abnormalities of the reproductive tract, and leg problems (Johnson, 1918a,b, 1919a,b,c, 1920a,b,c,d,e,f, 1921a,b,c,d, 1922a,b,c,d, 1923c,d,e,f, 1924a,b,c,d,e,f). A vaccine for fowlpox (then known as chickenpox) was produced by the Station and made available at cost to residents of the State of Washington (Johnson, 1920b). He also wrote several articles concerned with pathological conditions in cattle (Johnson, 1920g, 1921e,f, 1922e, 1923g).

Epidemiology and control

Johnson was the first person to point out that infection with Eimeria runs a self-limited course and observed, in language suitable for the layman, “if a large amount of infection is eaten at one time, enough development may take place in the intestinal tract to destroy the fowl”, whereas “if small amounts of infective material are consumed repeatedly, chronic disease occurs” (Johnson, 1923a). Subsequently, he showed that the severity of coccidiosis was related to the number of sporulated oocysts ingested (Johnson, 1927a). If this were not the case, then, “there would not seem to be much reason for advising thorough and frequent cleaning as a means of controlling this disease.” Four to 6 days were required before oocysts were passed in the faeces and 24 to 48 h for their sporulation, a process that required warmth, moisture and air. Oocysts remained viable for many weeks if putrefaction was prevented by storage in potassium dichromate, an idea provided by Philip Hadley (Johnson, 1927a). It had been suggested that the parasite could be transmitted in the egg but Johnson pointed out that, although contamination of the eggshell with oocysts may occur as eggs pass through the cloaca, transmission within the egg was highly improbable (Johnson, 1923a).

Johnson tested various chemicals and disinfectants and concluded that, without adequate sanitation, it is doubtful that the disease would ever be satisfactorily controlled (Johnson, 1923a). The feeding of milk products was thought to be beneficial because it was believed that fermentation in the intestine and consequent acidification of intestinal contents was detrimental to parasite development. Flocks given sour skimmed milk did not respond to treatment and, “actually developed the disease when such a feeding plan was in effect”. The most satisfactory treatment was catechu added to drinking water but he considered that treatment was only a secondary means of control, and that prevention was of far greater importance. Eradication of infection was impossible, “the best we can hope to do is to keep the disease down to a low degree.” Information was provided on transmission of infection within poultry houses and between neighbouring flocks. Although rearing fowls on the same yards year after year favoured coccidiosis, the disease could also occur on new premises. Infection could spread mechanically by means of dust, water, wind, wild birds, and so on. The significance of large unit size, high stocking density, restricted range, proximity of farms, and trafficking of poultry in transmission of coccidiosis was emphasized.

Miscellaneous conditions

Coccidiosis was generally thought to be responsible for diverse conditions including white diarrhoea of chicks, blackhead disease, and fowl paralysis. The causative agent of white diarrhoea was a germ that “does not live long under soil conditions as does—the one producing coccidiosis” (Johnson, 1924b). In the case of blackhead, “it can not be doubted that turkeys suffer with coccidiosis produced by a species of the genus Eimeria and that a coccidium is frequently found associated with blackhead, but it seems improbable that the coccidium has a direct relationship to production of blackhead” (Johnson, 1923a). “It is occasionally stated in the literature that the liver of chickens may show lesions of coccidiosis, the writer has not been able to verify such a statement” (Johnson, 1923/1924). Coccidiosis and paralysis were frequently found in the same bird but “this did not signify a causal relationship” (Johnson, 1928).

Host specificity

Coccidiosis was believed caused by a species of Eimeria (Eimeria avium) that infected many hosts including fowls, turkeys, pigeons, geese, ducks, pheasants, partridges, grouse, sparrows and rabbits (references in Chapman, 2003). Johnson, however, could not infect sparrows, turkeys, and ducks with E. avium and was unable to infect chickens with the “common coccidium of the rabbit.” Examination of the “common sparrow” revealed the presence of oocysts in the intestines that, “were not those of E. avium but an entirely different species which develops by the production of two sporocysts instead of four as found in the genus Eimeria” (Johnson, 1923a). He placed this parasite in the genus Cyclospora but, in a subsequent letter to Dr Wm. A. Riley, indicated that he was dealing with Isospora (Boughton, 1929). Tyzzer subsequently confirmed Johnson's suggestion that the form encountered in the turkey was a distinct species and gave it the name Eimeria meleagridis (Tyzzer, 1927).

The question of species

In 1923, the publications committee of the American Association of Instructors and Investigators in Poultry Husbandry asked Johnson to write an article on avian coccidiosis for readers of Poultry Science. Micrographs of oocysts of various sizes, sporozoites, merozoites, schizonts, gametocytes, and a drawing of a microgamete showing the characteristic flagellum were illustrated (Johnson, 1923/1924). Distinctly noticeable variations were seen in size, shape and structure of similar stages of apparently the same species of Eimeria, “the differences are often so marked as to suggest very strongly the probability of more than one species of coccidia being found in the chicken.” He qualifies this statement, however: “present information indicates that the same coccidium may be so variable that one can readily be misled to the belief that more than one species is being observed even when this is not true. As a matter of convenience and for the purpose of eliminating confusion as much as possible, only one species—Eimeria avium—is here recognized.”

Research at OSAES

Diseases of poultry had become one of the limiting factors in expansion of Oregon's commercial poultry industry (Anonymous, 1926b). A dilemma was that the Station had received 40 000 requests for tests for white diarrhoea, and large numbers of inquiries and personal visits, making it difficult to conduct research. Poultry men were advised that if they were patient for a few years so that uninterrupted investigations could be continued, the Station should be able to give them help. The hiring of Johnson enabled several projects to be initiated, and in addition to coccidiosis he carried out experiments on causes of lameness and bacillary white diarrhoea, and continued his studies of fowlpox.

New species

At the 2nd World Poultry Congress held in Ottawa, Canada in 1927, Johnson was asked to present a brief on coccidiosis to the Congress Poultry Disease Committee. He states, “two types of oocysts have been established on the basis of size, shape and colour. Two types have been established on the basis of prediliction—small intestine and cecal types” (Johnson, 1927b). Elsewhere he notes, “Tyzzer is of the opinion and offers definite information to substantiate it that chickens are hosts for two species of Eimeria—avium and tenella” (Johnson, 1927c). Tyzzer had presented this information at the second annual meeting of the American Society of Parasitologists held in Philadelphia in December 1926 (Tyzzer, 1927). In a bulletin published in December 1928 Johnson questioned the number of species of Eimeria in the chicken, “at least four kinds of chick-coccidia are found in Oregon flocks—three affecting the small intestine and one the ceca. The one causing severe small-intestine infection occurs more commonly in older growing stock and the cecal type more commonly in the younger fowls. Both types are capable of causing very severe hemorrhage” (Johnson, 1928). It is clear from this description that Johnson is referring to Eimeria necatrix and Eimeria tenella. In a footnote he indicates that he had communicated with Tyzzer earlier that year (in March 1928) and remarks, “It is of interest to note that fowls on the other side of the continent are also affected with four kinds of coccidian, possibly the same four occurring here.”

The most significant contribution to our knowledge of coccidiosis is arguably Johnson's description of two new species, for which the names Eimeria praecox and E. necatrix were proposed, and yet this finding is reported briefly in the director's biennial report for 1928 to 1930 (Anonymous, 1930b). Subsequently we learn that the names E. necatrix and E. praecox were suggested by Dr M. C. Hall of the Bureau of Animal Industry, United States Department of Agriculture, the former signifying murderess because of the extreme pathogenicity, and the latter signifying precocity because of early oocyst development (Johnson, 1938).

In the 1930 report, four other species were recognized from Oregon, Eimeria acervulina, Eimeria mitis, Eimeria maxima and E. tenella, all of which had been comprehensively described by Tyzzer (1929). Five of the six species were produced in pure culture but, despite a later reference to pure cultures of six species (Anonymous, 1938a), Johnson apparently did not have a pure culture of E. necatrix. We later learn that E. mitis, E. praecox, and E. tenella were isolated from “subcultures of a suspension prepared December 4 1926”, and E. maxima and E. acervulina “from subcultures of a culture prepared November 3 1926” (Johnson, 1938). Experiments with all six species (sporulation time, cross-immunization, and self-limitation) were carried out from May to August 1930. The information provided on E. praecox and E. necatrix is not widely available to the scientific community and is therefore now quoted in its entirety.

The average size of fifty oocysts of E. praecox was found to be 20.6×23.8 microns, or a shape index (width divided by length) of 0.87. The oocysts prove infective after twenty-four to thirty-six hour's sporulation at room temperature. New oocysts appear in the feces on the fourth day after feeding sporulated oocysts, a few hours sooner than with E. acervulina (Tyzzer). E. praecox attacks the small intestine, beginning near the gizzard. Failure in cross immunization has been established between E. praecox, E.mitis (Tyzzer), E. acervulina (Tyzzer) and E. maxima (Tyzzer). E. necatrix attacks the small intestine, beginning near the gizzard, and in severe infections produces marked hemorrhages and dilation of the intestine. The schizonts are the largest of any species attacking the duodenum and free portion of the small intestine. The average size of nine schizonts selected from a large number was 49.2×63.1 microns, and included a minimum of 42.0×44.0 microns and a maximum of 62.7×84.7 microns. (Anonymous, 1930b)

Tyzzer produced detailed descriptions of both E. necatrix and E. praecox (Tyzzer et al., 1932), and generously credits these two species to Johnson, “notwithstanding the brevity of his descriptions, it appears reasonably certain that the two species which we have independently discovered are E. praecox and E. necatrix of Johnson. While the dimensions furnished by Johnson are on the whole considerably greater than those obtained by Rivolta and by us, his association of large schizonts with the lesions of the small intestine in a distinctive disease appears to be an indication sufficient to establish his species, E. necatrix.”

In the posthumous bulletin, Johnson described the method he used to isolate pure species. This involved drawing single oocysts from a droplet of water into a fine capillary pipette, a method pioneered by Tyzzer (1931) that provided the groundwork for progress in the understanding of coccidiosis. He also provided dimensions of oocysts of five species, and these are presented in Table 1 with dimensions provided by Tyzzer (1929) and Tyzzer et al. (1932) for comparison. The bulletin was illustrated with superb photomicrographs of sporulated and unsporulated oocysts of six species, and an example for each is reproduced in Figures 2 and 3. Although Johnson illustrated oocysts of E. necatrix he did not provide dimensions presumably because his strain was not pure. Nevertheless, most of the oocysts depicted have comparable dimensions with those given for E. necatrix (14.2×16.7 μm) by Tyzzer et al. (1932).

Figure 2. Unsporulated and sporulated oocyst of (2a) E. acervulina, (2b) E. mitis, (2c) E. praecox (Johnson, 1938).

Figure 3. Unsporulated and sporulated oocyst of (3a) E. maxima, (3b) E. tenella, (3c) E. necatrix (Johnson, 1938).

Table 1. Measurements of oocysts of Eimeria species

		Dimensions (width×length [μm])
Species	Shape index^a	Minimum^b	Maximum^b	Average^b	Average^c
E. acervulina	0.77	12.0×14.0	14.8×20.0	13.8×18.0	14.3×19.5
E. mitis	0.91	12.0×13.0	16.0×18.0	13.7×15.0	15.5×16.2
E. praecox	0.87	19.0×22.0	22.0×25.0	20.6×23.8	17.1×21.3
E. maxima	0.75	20.0×26.4	27.6×36.0	22.9×30.4	22.6×29.3
E. tenella	0.74	15.0×20.0	19.4×25.0	17.5×23.7	19.0×22.6
^a Shape index of Johnson's strains obtained by dividing average width by length.
^b From Johnson (1938).
^c From Tyzzer (1929) and Tyzzer et al. (1932).

Immunity

Johnson was the first to investigate development of immunity to coccidial infection in the chicken (Johnson, 1927c). He used the term immunity to signify absolute insusceptibility to infection, and resistance to designate varying degrees of susceptibility. He compared birds reared commercially and in cages and found that, following challenge, those in cages were usually very susceptible whereas commercial birds more often possessed a high degree of resistance. Resistance to challenge in commercial birds was not due to age, but was shown to depend upon prior exposure to infection. Other interesting findings were that daily inoculations with two thousand or fewer sporulated oocysts resulted in resistance with less manifestation of disease than when larger numbers were given at greater intervals. He found that birds infected with oocysts obtained from the small intestine were not protected against challenge with oocysts derived from the caecum. Subsequently, he found no evidence of cross-immunization among E. mitis, E. acervulina, E. maxima, and E. praecox (Anonymous, 1930b; Johnson, 1938). Johnson was also interested in the occurrence of chronic avian coccidiosis, a phenomenon “pertaining to immunity”, that also attracted the attention of Tyzzer (Johnson, 1934; Tyzzer, 1949).

The relationship between immunity and occurrence of coccidiosis was also of interest: “the fact that resistance or immunity is produced as a result of previous infection explains why serious coccidiosis does not occur over a period of years on some farms where insanitary methods prevail” (Johnson, 1928). Rearing birds successfully at one farm under insanitary conditions, however, “does not signify that another would be equally successful with similar equipment and management.”

The possibility of immunizing birds against coccidiosis by administering gradually increasing numbers of oocysts was investigated: “a very definite immunity has been produced in this manner” (Anonymous, 1926b). By 1928, he had shown that repeated small doses produce a “very high resistance” and that “field tests on a practical scale already are supporting the experimental conclusions” (Anonymous, 1928). Pioneering studies were carried out with producing immunity by incorporating oocysts in feed and the results lent encouragement to feeding sporulated oocysts in wet mash as a practical means of immunization (Johnson, 1932). This research occupied the later years of his life: “considerable progress has been made and it is hoped that this means of control will be perfected and generally used, eliminating the chance inoculations now prevailing” (Johnson, 1933). “The viewpoint that actual inoculation of young stock on poultry farms, as a control measure, is becoming more valid as the facts regarding coccidiosis are ascertained. Nature's method seems to leave too much to chance to prove satisfactory. The recommendation to purposely infect by actually feeding oocysts involves a rather complicated procedure, the various angles of which must first be approached experimentally. The multiplicity of species certainly complicates the solution” (Johnson, 1938). In the preface to the posthumous bulletin, the director of OAES wrote that Johnson's work had shown that under experimental conditions chickens could be successfully immunized against five species of coccidia. These studies, “were cut short by his untimely death, thus leaving for others the accomplishment that not only had been his chief ambition but to which he gave his entire personal resources with heroic self-effacement.”

Effects on egg production

Although coccidiosis was considered primarily a disease of young birds, losses in egg production could occur in egg laying stock, “fowls which have not been infected during the rearing period may be disastrously affected in the laying-house” (Johnson, 1933). Egg production was slightly reduced in susceptible birds that had been infected with large doses of E. mitis and E. praecox, but ceased temporarily in birds infected with E. acervulina, E. maxima, and E. tenella (Johnson, 1931a). He was skeptical about the possibility of selecting fowls for resistance to coccidiosis since progeny of immune fowls were susceptible to infection.

Pullorum

In addition to his investigations of coccidiosis, Johnson was responsible for establishing a pullorum-testing laboratory in Oregon as part of the National Poultry Improvement Plan. He provided an informative account of the nature of the disease and testing methods employed (Johnson & Dickinson, 1933), and participated in a cooperative project with the University of British Columbia and WWAES concerned with accuracy of the agglutination test for detection of pullorum (Biely et al., 1931). His laboratory was graphically described by the local newspaper, “on most any morning but especially Monday, the north end hall on the second floor of the poultry building takes on the appearance typical of an opening day at a county fair—with chicken filled home constructed coops, hobbled turkeys, dead birds in boxes and sacks and especially constructed containers of blood filled test tubes blocking the entrance to the pathological laboratory. Into this three room laboratory come birds from all sections of the state to be autopsied, blood from entire flocks to be tested for pullorum disease and requests for fowl pox virus. The cool headed, busy bird doctor who often works until the wee hours of the morning to keep the hallway vacant for at least part of the day, was the discoverer of the fowl pox vaccination principle” (Oregon State Barometer, 28 October 1936).

Fowlpox

Johnson was also concerned with immunization of chickens and turkeys against fowlpox and was one of the first to vaccinate birds against this disease (Johnson, 1920b, 1921a, 1927d, 1929a,b, 1931b). The scale of work in Oregon is evident since from 1926 to 1930 approximately 270 000 chickens had successfully been vaccinated (105 000 by Johnson and 165 000 by the State Live Stock Sanitary Board) (Johnson, 1930). Johnson's contributions to immunization of chickens and turkeys against fowlpox have been reviewed by Beaudette (1949), who credited him with the introduction of fully virulent virus for vaccinating birds in the USA. Details of his methods, subsequently used extensively by others, were provided. Johnson's achievements were recognized by his invitation to review fowlpox at the 12th International Veterinary Congress held at the Waldorf-Astoria hotel in New York in August 1934 (Johnson, 1935). In the discussion following his paper, he questioned the viewpoint expressed by Doyle that vaccination with fowl virus is followed by a severe reaction (Anonymous, 1936). He considered that fowl virus was superior to pigeon virus and that he could not recommend the latter for use in the USA. He emphasized the need for a modified virus that would permit vaccination of laying flocks without affecting egg production.

The New York Congress was “a brilliant page in American veterinary history” as it broke all attendance records with thousands of delegates from the USA and around the world (Anonymous, 1934). Surely this must have been the high point of Johnson's career. Interestingly, Tyzzer's collaborators, Hans Theiler (who attended Johnson's session) and Elisabeth Jones, were also present at this meeting.

Discussion

Walter Johnson died after a long illness with intestinal cancer, 2 months after the death of another prominent parasitologist, H. B. Fantham, who was the first researcher to provide details of life-cycle stages of Eimeria in an avian host (Fantham, 1910). Johnson's work extended our knowledge of disease coccidiosis and his findings (self-limitation, host specificity, immunity, etc.) underlie methods developed for its control. In a report on the effect of research on Oregon's agricultural progress it was noted that coccidiosis was no longer a mysterious scourge to the Oregon poultry-man (Anonymous, 1937). Fowlpox could be controlled by a simple vaccination process developed at the experiment Station, a method that had been adopted and used in many other countries of the world besides the United States. The Director of OAES wrote that his death not only removed from the entire poultry industry a distinguished scientist and loyal friend, but also seriously delayed the investigational programme on 9 diseases of chickens (Anonymous, 1938b). H. J. Stafseth wrote, “much of what we know about avian coccidiosis should be credited to W.T. Johnson, Oregon, whose untimely death removed from our midst one of the outstanding research workers in this field” (Stafseth, 1949).

In the early years at WWAES Johnson produced numerous articles of an advisory nature concerned with poultry and their diseases. Through such means those involved in poultry production received current information and practical help to improve health of their flocks. At OSAES his research was primarily concerned with coccidiosis and fowlpox but he also ran a pullorum-testing laboratory for the State. He continued to provide advice to those involved with poultry through radio broadcasts and popular articles (Anonymous, 1926a; Johnson, 1929b,c). At the 1925 meeting of the AVMA held in Portland Oregon, his practical expertise was in evidence, “Johnson of the Oregon Experiment Station demonstrated methods of handling chickens with a skill that was amazing and lectured briefly on several important objectives of poultry practice” (Anonymous, 1925). At the AVMA clinic he showed that a Leghorn chicken could easily swallow a four-dram capsule.

In the classic paper in the American Journal of Hygiene, Tyzzer gave credit to Johnson for describing E. praecox and E. necatrix although he had also studied these species and provided a considerably more detailed account of their life cycles (Tyzzer et al., 1932). It is interesting to speculate on the extent to which Tyzzer's work prompted Johnson to publish his findings. There is no evidence that they ever met or attended the same scientific meetings and they came from different backgrounds: Johnson with training in veterinary science, Tyzzer from the medical school at Harvard University. In March 1928 Johnson had communicated with Tyzzer, who told him that fowls on the other side of the continent were affected by four species of coccidia. In the OSAES Bulletin published in December 1928 it was reported that at least four kinds of chick coccidia were present in Oregon flocks but Johnson had still not taken the decisive step in naming them. Perhaps the realization that Tyzzer was about to describe new species (and did so for E. acervulina, E. mitis, and E. maxima) prompted OSAES to publish the description of E. praecox and E. necatrix as soon as possible, thus explaining the limited amount of information provided for these species. Evidence that Johnson was working with five pure species by the end of 1930 indicates that he cannot have been far behind Tyzzer in his work on different species of Eimeria.

Scientific progress often occurs when two or more people are working in the same area, and this seems to be the case for Johnson and Tyzzer. It is remarkable that Johnson achieved as much as he did considering that he was running a routine diagnostic laboratory in addition to carrying out coccidiosis research. Although it seems likely that his work, as it relates to species identification, was influenced by Tyzzer's findings, we do not know whether Johnson's studies, such as those concerned with practical aspects of coccidiosis, influenced Tyzzer. A review of their publications indicates that both men had similar views with regard to many important issues (e.g. epidemiology, immunity, and control of coccidiosis). Both researchers had a rigorous approach to experimentation that was lacking in many of the studies carried out by others. Elery Becker wrote, “the works of Tyzzer, of Tyzzer, Theiler and Jones, and of Johnson represent a tremendous stride in knowledge concerning species, as well as host-parasite relationships, in avian coccidia” (Becker, 1934). The Oregon Barometer (1 August 1938) placed Johnson in elevated company, “It will remain for historians of the future to judge whether he is to occupy a niche in the hall of fame beside those of Pasteur and Koch.” Johnson's contributions may have received less attention than Tyzzer's, but they have also been of great importance for our understanding of coccidiosis.

Acknowledgments

The author would like to thank Mr L. A. Landis, University Archivist for Oregon State University Library for providing a copy of Johnson's personnel file, and articles from the campus newspaper Barometer, and Mr. L. R. Stark, Assistant Archivist for Washington State University Holland/New library for providing copies of Johnson's early publications. The author also thanks Dr A. S. Rosenwald for providing personal memories of Johnson.