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Combined Infections of Calves with the Nematode Parasites Trichostrongylus Axei and Ostertagia Ostertagi
Br. vet.
J. (1968),
1240
299
COMBINED INFECTIONS OF CALVES WITH THE NEMATODE PARASITES TRICHOSTRONGYLUS AXEl AND OSTERTAGIA OSTERTAGI By J. G. Ross, A. PURCELL, J. R. TODD AND C. Dow Veterinary Research Laboratories, Stormont, Belfast, Northern Ireland
SUMMARY Parasite-free calves were infected at 6-8 weeks of age with either 150,000 T. axei or 150,000 O. ostertagi third-stage larvae, or varying time combinations of 100,000 T. axei and 50,000 O. ostertagi third-stage larvae. All of the calves developed a severe diarrhoea between the second and third week of infection and either died or were slaughtered in extremis by the eighth week. The clinical pathology, gross and histopathology of the infections are described. Differences in serum pepsinogen levels were observed following varying infection patterns and it was possible on gross pathology to distinguish distinctive lesions resulting from differences in percentage of infection of the two parasites.
INTRODUCTION Dual infections of cattle with Trichostrongylus axei and Ostertagia ostertagi are common in Northern Ireland and are the cause of clinical disease and deaths in yearlings in the autumn (Ross, 1965). Sufficient information is available on the clinical pathology, histopathology and parasite development of pure experimental infections with T. axei (Doran, 1955; Leland, Drudge & Wyant, 1958; Ross, Purcell, Dow & Todd, 1967, 1968), and with O. ostertagi (Martin, Thomas & Urquhart, 1957; Ross, 1963; Ross & Dow, 1965; Ross & Todd, 1965), to permit an adequate assessment of combined infections. While both these parasites have been shown to produce emaciation, diarrhoea and death in association with a marked rise in abomasal pH (Ross & Todd, 1965; Jennings, Armour, Lawson & Roberts, 1966; Ross et al., 1968), they differ in the type of lesion they produce in the abomasum and in their developmental site within the abomasal mucosa (Ross & Dow, 1965; Ross et al., 1967). It is of interest and of importance to determine if the parasites are competitive and to what degree dual infections have an additive detrimental effect on the host. MATERIALS AND METHODS Sixteen Ayrshire cross calves were reared parasite-free and at 6-8 weeks of age were given oral infections of third-stage infective larvae of T. axei or O. ostertagi as shown in Table 1.
""8
TABLE I
Initial infection
Calf No.
Interval between infections
Post mortem T. axei Second irifection
Count (thousands)
Percentage take
Post mortem Count (thousands)
o. ostertagi Percentage take
Abomasal
pH
Infection length (weeks)
I;J:j
Fate·
::0 ..... >-l ..... rJl
::r: 2 3 4 5 6 7 8 9 10 II
12 13 14 15 16
150,000 O. ost. 150,000 O. ost. 150,000 T. axei 150,000 T . axei 150,000 T. axei 50,000 O. oslo 50,000 O. ost. 50,000 O. ost. 100,000 T. axei 100,000 T. axei 100,000 T . axei 100,000 T. axei 100,000 T. axei 100,000 T. axei 100,000 T. axei 100,000 T. axei
• Survival
=
3 3 3 0 2 3 3 3 3 3
Nil Nil Nil Nil Nil 100,000 T . axei 100,000 T. axei 100,000 T. axei 50,000 O. ost. 50,000 O. ost. 50,000 O. ost. 50,000 O. ost. 50,000 O. ost. 50,000 O. ost. 50,000 O. ost. 50,000 O. ost.
S ; slaughtered in extremis or died
=
D.
16·5 37·5 15"8 76.1 28·0 26·7 21·4 36.5 25.6 10·2 24.8 5.2 52·6 13·9 36.0 50.8
10 51 18·6 27 21 37 26 10
25 5 53 14 36 51
22·1 23.8 22·5 9.8 10·0 g·1 5·9 19·5 19.8 13·4 1·1
II
25
44 48 45 26 20 18 12 39 40 27 2
8·0 3·5 8·4 8·0 6·0 7·5 7·5 4·5 4·5 9.0 8·5 8·5 8·0
3 6 3 3 8 8 8 8 8 6·5 6 8 8 4 04-
D D S D D S S S S S D D D D D D
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::0 .....
~
1...0
0 C ::0 Z
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s-' ;; ~
"
"
NEMATODE INFECTIONS OF CALVES
301
The calves were weighed at the time of infection and blood samples were collected weekly on which erythrocyte and serological estimates were performed as previously described (Ross & Todd, 1965). At the time of slaughter the abomasum and first foot of the small intestine were removed entire, the pH of the abomasal contents measured and the worms recovered, differentiated, counted and measured as previously indicated (Ross & Todd, 1965). Serum pepsinogen levels were determined as previously described (Ross et al., 1967). Calves in extremis were slaughtered so that abomasal pH could be recorded. Such calves are referred to in the text as having died.
RESULTS
Clinical All calves given 150,000 T. axei or 150,000 O. ostertagi developed a severe diarrhoea between the sixteenth and twenty-first day after infection. Calves given 100,000 T. axei did not develop diarrhoea until 2-10 days after a challenge infection with 50,000 O. ostertagi. Calves given 100,000 T. axei following an earlier infection with 50,000 O. ostertagi developed a mild diarrhoea 1 week after the challenge infection. As diarrhoea developed the calves lost condition and became extremely dehydrated. All of the calves, except NO.1 which died 1 week after an infection of 150,000 O. ostertagi, developed some degree of diarrhoea. Both of the calves infected with 150,000 O. ostertagi died, two of three of the calves given 150,000 T. axei died, and all of the calves given 50,000 O. ostertagi died 2-3 weeks following 100,000 T. axei. Calves given mixed infections or an O. ostertagi infection 1 week following a T. axei infection or an O. ostertagi prior to a T. axei infection survived, although the latter group of calves were very weak as a result of the infections. Details of the results of infections are shown in Table 1. Clinical pathology The major difference in the clinical pathology between the various types of infection was observed in the serum pepsinogen levels. This is illustrated in Fig. 1. Where no calves survived to 8 weeks, data from previous infections have been used (Ross et at., 1968). With a pure T. axei infection a small but steady rise was observed to a maximum serum pepsinogen level of about 2'0 i.u. /I. at the third week. A similar but greater rise was observed in pure O. ostertagi infections to a peak level of around 4'0 i.u. /I. at the third week followed by an irregular fall. Where a T. axei infection was given 3 weeks following an initial O. ostertagi infection, a further sustained rise in the serum pepsinogen level occurred 1 week after the T . axei challenge infection to a peak level of around 4'5 i.u· /I. While this level fell it was, however, maintained at about 3'0 i.u. /I. until 8 weeks after infection. Where an O. ostertagi infection was given 3 weeks after an initial infection of T. axei, the rise initiated by the first infection was maintained to give a peak level of around 5"0 i.u. /I. at the seventh to eighth week.
BRITISH VETERINARY JOURNAL, 124, 7
302
t:s......- - 6
6
£7----6
5
O. ostertag; following T. axe; T. ax(!; following O.ostertag; O. ostertag; only
------ T.ax(!; only
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I
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\
I
c
o
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I
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"CD (I)
o Infection length (weeks) Fig.
I.
Comparative serum pepsinogen levels in pure and mixed infections.
Post-mortem findings Details of worm burdens and abomasal pH values for individual calves are shown in Table I. As previously observed in individual infections with each of the parasites, a rise in abomasal pH was associated with clinical and lethal infections (Ross & Todd, 1965; Ross et at., 1968). There was no evidence to suggest that the existence of infection with one parasite produced retardation in the development of a subsequent infection with the other parasite. There is, however, some indication that in simultaneous infections or where O. ostertagi was superimposed on an existing T. axei infection that a reduced number of O. ostertagi became established. The gross appearance of the abomasal mucosa in the various infections was as follows : Pure O. ostertagi infections. The mucosa was dark red in colour, severely congested and covered with numerous individual and coalesced white nodules. Slight oedema was present and the extent and severity of the lesions varied with the length of infection (Ross & Dow, 1965). Pure T. axei infections. The entire mucosa was a dark purple in colour and severely congested. Large areas were covered with a white/red diphtheritic exudate which gave the mucosa a necrotic "scalded" appearance. White raised plaque lesions were not readily discernible except where the mucosa was scraped and meticulously examined (Ross et at., 1967, 1968).
PLATE I
Fig.
2.
Sec tion of mu cosa in com bined infec tion lesions produced by th e histotrophic phases of both parasites. H & E X 100.
Fig. 3. Fundus of abomasum from calf given simultaneous infection of T . axei and O. ostertagi. The characteristi c yellow mushroom type nodu les a re visible against the background of th e severely conges ted mu cosa.
R oss, Purcell, Todd a nd D ow, B r. vet.
J.
( 1968), 124, 7
NEMATODE INFECTIONS OF CALVES
Simultaneous or week interval mixed infections. The lesions observed in these infections were particularly striking. The mucosa was dark red in colour, wet and covered with a clear mucus. The nodules produced by the O. ostertagi infection in the fundus were dearly visible and covered with coat of yellow diphtheritic material. Where groups of nodules were adjacent this produced a mat of yellow necrotic material. The individual nodules had the appearance of yellow mushrooms on the red mucosal background. The yellow necrotic material was easily removed and revealed a normal white nodule underneath (Fig. 2). O. ostertagi irifection followed by T. axei. The mucosa was congested and dark red in colour. The folds of the fundus were thickened and oedematous and flattened "cobblestone" lesions of O. o~tertagi were visible on and between the T. axei infection. T. axei infection followed by O. ostertagi. On first examination the mucosa appeared similar to the red "scalded" appearance of a pure T. axei infection. However, when the mucus coat was removed distinct nodules could be easily distinguished in the mucosa. The histopathology of the lesions produced by both T. axei and O. ostertagi when given in combined infections was similar to that produced by pure infections. O. ostertagi produced dilation and rupture of the gastric glands while T. axei caused desquamation and necrosis of the epithelium of the gastric pits (Ross & Dow, 1964; Ross et al., 1968) (Fig. 2). DISCUSSION
The results do not suggest that a direct nutritional or site competition exists between the two parasites, although limitation of "living room" which will determine the threshold and lethal level of infection will apply equally to combined as to pure infections (Ross et at., 1968). Previous investigations with O. circumcincta and T. axei mixed infections in sheep also demonstrated a lack of competition between Ostertagia and Trichostrongylus species of parasites (Kates, Wilson & Turner, 1957). Earlier observations have shown that while O. ostertagi fourth-stage larvae develop within the lumen of the gastric glands, T. axei fourth stages develop superficially between the abomasal mucosal cells and the basement membrane, and do not suggest nutritional competition during the histotropic phase of these parasites. There was, however, evidence that where infection with O. ostertagi followed an initial infection of T. axei, particularly within 2 weeks, that the percentage of O. ostertagi infection which became established, was reduced. In the light of lack of evidence for competition in the other mixed infections it must be concluded that the reaction or the mucus coat produced by the initial T. axei infection in some manner interfered with tpe establishment of the subsequent infection, and that this did not indicate a direct nutritional or site competition between the two parasite species. Inhibited development was not a feature of infection with either parasite, and its absence further demonstrated the lack of nutritional or site competition between these parasites.
BRITISH VETERINARY JOURNAL, 124, 7
There is evidence to suggest that O. ostertagi is marginally more pathogenic than T. axei and that an increase in pathogenicity is produced by an O. ostertagi infection following an initial T. axei infection, or by a low level infection superimposed on a high infection. There was, however, considerable variation in the lethal worm burden between calves and the results on this aspect are not conclusive. O. ostertagi damages all depths of the mucosa when it emerges from the gastric glands (Ross & Dow, 1965), T. axei produces sloughing of the upper third of the abomasal mucosa as the immature stages develop between the mucosal cells and the basement membrane (Ross et at., 1968). Both parasites produce extensive damage to the abomasal mucosa, a loss of zymogen and parietal cells in the gastric glands, resulting in a rise in abomasal pH, diarrhoea, and death where infection levels are sufficiently high. The variation in serum pepsinogen levels resulting from the different infections is of particular interest. Within the calf groups in this experiment it was possible to distinguish the predominant species of parasite by these levels, provided the calf had been infected for at least 3 weeks. Diagnosis of infections in the field presents considerable difficulty and the use of serum pepsinogen estimates may be a useful aid. There are, however, many unknown factors concerning the basis of variation in serum pepsinogen levels, and cattle free from infection with either parasite have been observed with high serum pepsinogen levels (Ross & Todd, unpublished observations), so that its interpretation must be made with caution. The appearance of the abomasal mucosa at autopsy is a useful guide to the level of third-stage larvae infection and to the parasite species involved. There is little doubt that varying levels and combinations of infection, as occur in the field, will produce various intermediate lesions from those described here. The predominant O. ostertagi and T. axei lesions have already been described (Ross & Dow, 1965; Ross et at., 1967, 1968). The striking necrotic lesion produced by simultaneous infections by these parasites has not previously been described and is not uncommon in natural field infections. The masking of typical O. ostertagi nodules by the more superficial necrotic T. axei lesion in mixed infections is important in routine post-mortem examinations. It is imperative that the diphtheritic mucus coat associated with infections with T. axei is removed from the abomasal mucosa in order to determine the relative infection levels with these parasites on gross examination. REFERENCES
DORAN, D. j. ( 1955). Am.]. vet. Res., 16,401. JENNINGS, F. W., ARMOUR, j ., LAWSON, D. D. & ROBERTS, R . ( 1966). Am. ]. vet. Res., 27, 12 49. KATES, K. C., WILSON, G. I. & TURNER,j. H. ( 1957). Arum. Husb. Sect., South. Agric. Workers, 4. LELAND, S. E., DRUDGE, j. H. & WYANT, Z. N. (1958).]. Parasitol., 44 (2), 27. MARTIN, W. B., THOMAS, B. A. C. & URQUHART, G. M. (1957). Vet. Rec., fig, 736. Ross,j. G. (1963) . Vet. Rec., 77, 16. Ross, j. G. & Dow, C. (1965). Br. vet. ] ., HU, 228. Ross, j. G. & TODD, j. R. ( 1965)' Br. vet. ]., 121,55. Ross,j. G., PURCELL, A., Dow, C. & TODD,j. R. (1967). Res. vet. Sci., 8, 201. Ross, j . G., PURCELL, A., Dow, C. & TODD, j. R. (1968). Res. vet. Sci., 9, 314. (Accepted for publication 12th December 1967 )
NEMATODE INFECTIONS OF CALVES
30 5
Infections cotnbinees par les netnatodes Trichostrongylus axei et Ostertagia ostertagi chez des veaux (Ross et al.) ResUtne. Des veaux exempts de parasites ont ete infestes, entre 6 et 8 semaines, de larves au
troisieme stade dans les proportions suivantes: soit 150.000 larves de T. axei, soit 150.000 larves de O. ostertagi, soit des combinaisons de 100.000 larves au troisieme stade de T. axei et de 50 . 000 de O. ostertagi, effectuees a des periodes diverses. Dans tous les cas, une violente diarrhee s'est declaree au cours de la deuxieme ou de la troisieme semaine de l'infection; puis les veaux sont morts ou ont ete abattus in extremis a la huitieme semaine. L'expose decrit la pathologie clinique et l'histopathologie de ces infections. On a observe les differences entre les niveaux pepsinogenes du serum, a la suite de diverses formes de developpement des infections, et il a ete possible de distinguer des lesions particulieres resultant de la difference dans les pourcentages d'infection des deux parasites, grace a l'etude de la pathologie. Kotnbinierte Infektion von KaIbern tnit den Netnatode-Parasiten Trichostrongylus axei und Ostertagia ostertagi (Ross et al.) Zusatntnenfassung. Parasitenfreie Kalber wurden im Alter von 6-8 Wochen mit entweder 150.000 T. axei oder 150.000 O. ostertagi Larven im dritten Stadium, oder in verschiedenen Zeitabschnitten mit 100.000 T. axei und 50.000 O. ostertagi Larven im dritten Stadium infiziert.
Aile Kalber entwickelten zwischen del' zweiten und dritten Woche nach der Infektion eine schwere Diarrhoea und starben oder mussten bis zur achten Woche in extremis geschlachtet werden. Die klinische Pathologie, allgemeine und Histopathologie del' Infektionen werden beschrieben. Verschiedene Serum Pepsinogen Grade wurden je nach den veranderten Infektions-Mustern befolgt, und durch die allgemeine Pathologie war es maglich, spezifische Verletzungen wahrzunehmen, die durch die prozentuell unterschiedlichen Infektionen der zwei Parasiten hervorgerufen wurden. Infeccions cotnbinadas de terneros con los parasitos netnatodos Trichostrongylus axei y Ostertagia ostertagi (Ross et al.) ResUtnen. Fueron infectados terneros libres de panisitos, a 6-8 semanas de edad, con 150.000 larvas de T. axei 0 con 150.000 larvas de O. ostertagi, de tercer estadio, 0 bien combinaciones a tiempos varios de 100.000 larvas de T. axei Y 50.000 larvas de O. ostertagi, de tercer estadio.
En todos los animals se produjo grave diarrea entre la segunda Y la tercera semana de la infeccion, Y murieron 0 se llevaron in extremis a la matanza para la octava semana. Se describen la patologia clinica, la patologia gruesa y la histopatologia de las infecciones. Se observaron las diferencias en los niveles de pepsinogeno del suero despues de las diversas estructuras de la infeccion, siendo posible en la patologia gruesa distinguir claras lesiones resultantes de la diferencia en el porcentaje de infeccion de los dos parasitos.
J. (1968),
1240
299
COMBINED INFECTIONS OF CALVES WITH THE NEMATODE PARASITES TRICHOSTRONGYLUS AXEl AND OSTERTAGIA OSTERTAGI By J. G. Ross, A. PURCELL, J. R. TODD AND C. Dow Veterinary Research Laboratories, Stormont, Belfast, Northern Ireland
SUMMARY Parasite-free calves were infected at 6-8 weeks of age with either 150,000 T. axei or 150,000 O. ostertagi third-stage larvae, or varying time combinations of 100,000 T. axei and 50,000 O. ostertagi third-stage larvae. All of the calves developed a severe diarrhoea between the second and third week of infection and either died or were slaughtered in extremis by the eighth week. The clinical pathology, gross and histopathology of the infections are described. Differences in serum pepsinogen levels were observed following varying infection patterns and it was possible on gross pathology to distinguish distinctive lesions resulting from differences in percentage of infection of the two parasites.
INTRODUCTION Dual infections of cattle with Trichostrongylus axei and Ostertagia ostertagi are common in Northern Ireland and are the cause of clinical disease and deaths in yearlings in the autumn (Ross, 1965). Sufficient information is available on the clinical pathology, histopathology and parasite development of pure experimental infections with T. axei (Doran, 1955; Leland, Drudge & Wyant, 1958; Ross, Purcell, Dow & Todd, 1967, 1968), and with O. ostertagi (Martin, Thomas & Urquhart, 1957; Ross, 1963; Ross & Dow, 1965; Ross & Todd, 1965), to permit an adequate assessment of combined infections. While both these parasites have been shown to produce emaciation, diarrhoea and death in association with a marked rise in abomasal pH (Ross & Todd, 1965; Jennings, Armour, Lawson & Roberts, 1966; Ross et al., 1968), they differ in the type of lesion they produce in the abomasum and in their developmental site within the abomasal mucosa (Ross & Dow, 1965; Ross et al., 1967). It is of interest and of importance to determine if the parasites are competitive and to what degree dual infections have an additive detrimental effect on the host. MATERIALS AND METHODS Sixteen Ayrshire cross calves were reared parasite-free and at 6-8 weeks of age were given oral infections of third-stage infective larvae of T. axei or O. ostertagi as shown in Table 1.
""8
TABLE I
Initial infection
Calf No.
Interval between infections
Post mortem T. axei Second irifection
Count (thousands)
Percentage take
Post mortem Count (thousands)
o. ostertagi Percentage take
Abomasal
pH
Infection length (weeks)
I;J:j
Fate·
::0 ..... >-l ..... rJl
::r: 2 3 4 5 6 7 8 9 10 II
12 13 14 15 16
150,000 O. ost. 150,000 O. ost. 150,000 T. axei 150,000 T . axei 150,000 T. axei 50,000 O. oslo 50,000 O. ost. 50,000 O. ost. 100,000 T. axei 100,000 T. axei 100,000 T . axei 100,000 T. axei 100,000 T. axei 100,000 T. axei 100,000 T. axei 100,000 T. axei
• Survival
=
3 3 3 0 2 3 3 3 3 3
Nil Nil Nil Nil Nil 100,000 T . axei 100,000 T. axei 100,000 T. axei 50,000 O. ost. 50,000 O. ost. 50,000 O. ost. 50,000 O. ost. 50,000 O. ost. 50,000 O. ost. 50,000 O. ost. 50,000 O. ost.
S ; slaughtered in extremis or died
=
D.
16·5 37·5 15"8 76.1 28·0 26·7 21·4 36.5 25.6 10·2 24.8 5.2 52·6 13·9 36.0 50.8
10 51 18·6 27 21 37 26 10
25 5 53 14 36 51
22·1 23.8 22·5 9.8 10·0 g·1 5·9 19·5 19.8 13·4 1·1
II
25
44 48 45 26 20 18 12 39 40 27 2
8·0 3·5 8·4 8·0 6·0 7·5 7·5 4·5 4·5 9.0 8·5 8·5 8·0
3 6 3 3 8 8 8 8 8 6·5 6 8 8 4 04-
D D S D D S S S S S D D D D D D
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>-l t>1
::0 .....
~
1...0
0 C ::0 Z
>
s-' ;; ~
"
"
NEMATODE INFECTIONS OF CALVES
301
The calves were weighed at the time of infection and blood samples were collected weekly on which erythrocyte and serological estimates were performed as previously described (Ross & Todd, 1965). At the time of slaughter the abomasum and first foot of the small intestine were removed entire, the pH of the abomasal contents measured and the worms recovered, differentiated, counted and measured as previously indicated (Ross & Todd, 1965). Serum pepsinogen levels were determined as previously described (Ross et al., 1967). Calves in extremis were slaughtered so that abomasal pH could be recorded. Such calves are referred to in the text as having died.
RESULTS
Clinical All calves given 150,000 T. axei or 150,000 O. ostertagi developed a severe diarrhoea between the sixteenth and twenty-first day after infection. Calves given 100,000 T. axei did not develop diarrhoea until 2-10 days after a challenge infection with 50,000 O. ostertagi. Calves given 100,000 T. axei following an earlier infection with 50,000 O. ostertagi developed a mild diarrhoea 1 week after the challenge infection. As diarrhoea developed the calves lost condition and became extremely dehydrated. All of the calves, except NO.1 which died 1 week after an infection of 150,000 O. ostertagi, developed some degree of diarrhoea. Both of the calves infected with 150,000 O. ostertagi died, two of three of the calves given 150,000 T. axei died, and all of the calves given 50,000 O. ostertagi died 2-3 weeks following 100,000 T. axei. Calves given mixed infections or an O. ostertagi infection 1 week following a T. axei infection or an O. ostertagi prior to a T. axei infection survived, although the latter group of calves were very weak as a result of the infections. Details of the results of infections are shown in Table 1. Clinical pathology The major difference in the clinical pathology between the various types of infection was observed in the serum pepsinogen levels. This is illustrated in Fig. 1. Where no calves survived to 8 weeks, data from previous infections have been used (Ross et at., 1968). With a pure T. axei infection a small but steady rise was observed to a maximum serum pepsinogen level of about 2'0 i.u. /I. at the third week. A similar but greater rise was observed in pure O. ostertagi infections to a peak level of around 4'0 i.u. /I. at the third week followed by an irregular fall. Where a T. axei infection was given 3 weeks following an initial O. ostertagi infection, a further sustained rise in the serum pepsinogen level occurred 1 week after the T . axei challenge infection to a peak level of around 4'5 i.u· /I. While this level fell it was, however, maintained at about 3'0 i.u. /I. until 8 weeks after infection. Where an O. ostertagi infection was given 3 weeks after an initial infection of T. axei, the rise initiated by the first infection was maintained to give a peak level of around 5"0 i.u. /I. at the seventh to eighth week.
BRITISH VETERINARY JOURNAL, 124, 7
302
t:s......- - 6
6
£7----6
5
O. ostertag; following T. axe; T. ax(!; following O.ostertag; O. ostertag; only
------ T.ax(!; only
,pr---~, I
4
I I
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I
CD Cl C
\
I
c
o
\
I
3
tn Q.
CD Q.
E
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:::l
"CD (I)
o Infection length (weeks) Fig.
I.
Comparative serum pepsinogen levels in pure and mixed infections.
Post-mortem findings Details of worm burdens and abomasal pH values for individual calves are shown in Table I. As previously observed in individual infections with each of the parasites, a rise in abomasal pH was associated with clinical and lethal infections (Ross & Todd, 1965; Ross et at., 1968). There was no evidence to suggest that the existence of infection with one parasite produced retardation in the development of a subsequent infection with the other parasite. There is, however, some indication that in simultaneous infections or where O. ostertagi was superimposed on an existing T. axei infection that a reduced number of O. ostertagi became established. The gross appearance of the abomasal mucosa in the various infections was as follows : Pure O. ostertagi infections. The mucosa was dark red in colour, severely congested and covered with numerous individual and coalesced white nodules. Slight oedema was present and the extent and severity of the lesions varied with the length of infection (Ross & Dow, 1965). Pure T. axei infections. The entire mucosa was a dark purple in colour and severely congested. Large areas were covered with a white/red diphtheritic exudate which gave the mucosa a necrotic "scalded" appearance. White raised plaque lesions were not readily discernible except where the mucosa was scraped and meticulously examined (Ross et at., 1967, 1968).
PLATE I
Fig.
2.
Sec tion of mu cosa in com bined infec tion lesions produced by th e histotrophic phases of both parasites. H & E X 100.
Fig. 3. Fundus of abomasum from calf given simultaneous infection of T . axei and O. ostertagi. The characteristi c yellow mushroom type nodu les a re visible against the background of th e severely conges ted mu cosa.
R oss, Purcell, Todd a nd D ow, B r. vet.
J.
( 1968), 124, 7
NEMATODE INFECTIONS OF CALVES
Simultaneous or week interval mixed infections. The lesions observed in these infections were particularly striking. The mucosa was dark red in colour, wet and covered with a clear mucus. The nodules produced by the O. ostertagi infection in the fundus were dearly visible and covered with coat of yellow diphtheritic material. Where groups of nodules were adjacent this produced a mat of yellow necrotic material. The individual nodules had the appearance of yellow mushrooms on the red mucosal background. The yellow necrotic material was easily removed and revealed a normal white nodule underneath (Fig. 2). O. ostertagi irifection followed by T. axei. The mucosa was congested and dark red in colour. The folds of the fundus were thickened and oedematous and flattened "cobblestone" lesions of O. o~tertagi were visible on and between the T. axei infection. T. axei infection followed by O. ostertagi. On first examination the mucosa appeared similar to the red "scalded" appearance of a pure T. axei infection. However, when the mucus coat was removed distinct nodules could be easily distinguished in the mucosa. The histopathology of the lesions produced by both T. axei and O. ostertagi when given in combined infections was similar to that produced by pure infections. O. ostertagi produced dilation and rupture of the gastric glands while T. axei caused desquamation and necrosis of the epithelium of the gastric pits (Ross & Dow, 1964; Ross et al., 1968) (Fig. 2). DISCUSSION
The results do not suggest that a direct nutritional or site competition exists between the two parasites, although limitation of "living room" which will determine the threshold and lethal level of infection will apply equally to combined as to pure infections (Ross et at., 1968). Previous investigations with O. circumcincta and T. axei mixed infections in sheep also demonstrated a lack of competition between Ostertagia and Trichostrongylus species of parasites (Kates, Wilson & Turner, 1957). Earlier observations have shown that while O. ostertagi fourth-stage larvae develop within the lumen of the gastric glands, T. axei fourth stages develop superficially between the abomasal mucosal cells and the basement membrane, and do not suggest nutritional competition during the histotropic phase of these parasites. There was, however, evidence that where infection with O. ostertagi followed an initial infection of T. axei, particularly within 2 weeks, that the percentage of O. ostertagi infection which became established, was reduced. In the light of lack of evidence for competition in the other mixed infections it must be concluded that the reaction or the mucus coat produced by the initial T. axei infection in some manner interfered with tpe establishment of the subsequent infection, and that this did not indicate a direct nutritional or site competition between the two parasite species. Inhibited development was not a feature of infection with either parasite, and its absence further demonstrated the lack of nutritional or site competition between these parasites.
BRITISH VETERINARY JOURNAL, 124, 7
There is evidence to suggest that O. ostertagi is marginally more pathogenic than T. axei and that an increase in pathogenicity is produced by an O. ostertagi infection following an initial T. axei infection, or by a low level infection superimposed on a high infection. There was, however, considerable variation in the lethal worm burden between calves and the results on this aspect are not conclusive. O. ostertagi damages all depths of the mucosa when it emerges from the gastric glands (Ross & Dow, 1965), T. axei produces sloughing of the upper third of the abomasal mucosa as the immature stages develop between the mucosal cells and the basement membrane (Ross et at., 1968). Both parasites produce extensive damage to the abomasal mucosa, a loss of zymogen and parietal cells in the gastric glands, resulting in a rise in abomasal pH, diarrhoea, and death where infection levels are sufficiently high. The variation in serum pepsinogen levels resulting from the different infections is of particular interest. Within the calf groups in this experiment it was possible to distinguish the predominant species of parasite by these levels, provided the calf had been infected for at least 3 weeks. Diagnosis of infections in the field presents considerable difficulty and the use of serum pepsinogen estimates may be a useful aid. There are, however, many unknown factors concerning the basis of variation in serum pepsinogen levels, and cattle free from infection with either parasite have been observed with high serum pepsinogen levels (Ross & Todd, unpublished observations), so that its interpretation must be made with caution. The appearance of the abomasal mucosa at autopsy is a useful guide to the level of third-stage larvae infection and to the parasite species involved. There is little doubt that varying levels and combinations of infection, as occur in the field, will produce various intermediate lesions from those described here. The predominant O. ostertagi and T. axei lesions have already been described (Ross & Dow, 1965; Ross et at., 1967, 1968). The striking necrotic lesion produced by simultaneous infections by these parasites has not previously been described and is not uncommon in natural field infections. The masking of typical O. ostertagi nodules by the more superficial necrotic T. axei lesion in mixed infections is important in routine post-mortem examinations. It is imperative that the diphtheritic mucus coat associated with infections with T. axei is removed from the abomasal mucosa in order to determine the relative infection levels with these parasites on gross examination. REFERENCES
DORAN, D. j. ( 1955). Am.]. vet. Res., 16,401. JENNINGS, F. W., ARMOUR, j ., LAWSON, D. D. & ROBERTS, R . ( 1966). Am. ]. vet. Res., 27, 12 49. KATES, K. C., WILSON, G. I. & TURNER,j. H. ( 1957). Arum. Husb. Sect., South. Agric. Workers, 4. LELAND, S. E., DRUDGE, j. H. & WYANT, Z. N. (1958).]. Parasitol., 44 (2), 27. MARTIN, W. B., THOMAS, B. A. C. & URQUHART, G. M. (1957). Vet. Rec., fig, 736. Ross,j. G. (1963) . Vet. Rec., 77, 16. Ross, j. G. & Dow, C. (1965). Br. vet. ] ., HU, 228. Ross, j. G. & TODD, j. R. ( 1965)' Br. vet. ]., 121,55. Ross,j. G., PURCELL, A., Dow, C. & TODD,j. R. (1967). Res. vet. Sci., 8, 201. Ross, j . G., PURCELL, A., Dow, C. & TODD, j. R. (1968). Res. vet. Sci., 9, 314. (Accepted for publication 12th December 1967 )
NEMATODE INFECTIONS OF CALVES
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Infections cotnbinees par les netnatodes Trichostrongylus axei et Ostertagia ostertagi chez des veaux (Ross et al.) ResUtne. Des veaux exempts de parasites ont ete infestes, entre 6 et 8 semaines, de larves au
troisieme stade dans les proportions suivantes: soit 150.000 larves de T. axei, soit 150.000 larves de O. ostertagi, soit des combinaisons de 100.000 larves au troisieme stade de T. axei et de 50 . 000 de O. ostertagi, effectuees a des periodes diverses. Dans tous les cas, une violente diarrhee s'est declaree au cours de la deuxieme ou de la troisieme semaine de l'infection; puis les veaux sont morts ou ont ete abattus in extremis a la huitieme semaine. L'expose decrit la pathologie clinique et l'histopathologie de ces infections. On a observe les differences entre les niveaux pepsinogenes du serum, a la suite de diverses formes de developpement des infections, et il a ete possible de distinguer des lesions particulieres resultant de la difference dans les pourcentages d'infection des deux parasites, grace a l'etude de la pathologie. Kotnbinierte Infektion von KaIbern tnit den Netnatode-Parasiten Trichostrongylus axei und Ostertagia ostertagi (Ross et al.) Zusatntnenfassung. Parasitenfreie Kalber wurden im Alter von 6-8 Wochen mit entweder 150.000 T. axei oder 150.000 O. ostertagi Larven im dritten Stadium, oder in verschiedenen Zeitabschnitten mit 100.000 T. axei und 50.000 O. ostertagi Larven im dritten Stadium infiziert.
Aile Kalber entwickelten zwischen del' zweiten und dritten Woche nach der Infektion eine schwere Diarrhoea und starben oder mussten bis zur achten Woche in extremis geschlachtet werden. Die klinische Pathologie, allgemeine und Histopathologie del' Infektionen werden beschrieben. Verschiedene Serum Pepsinogen Grade wurden je nach den veranderten Infektions-Mustern befolgt, und durch die allgemeine Pathologie war es maglich, spezifische Verletzungen wahrzunehmen, die durch die prozentuell unterschiedlichen Infektionen der zwei Parasiten hervorgerufen wurden. Infeccions cotnbinadas de terneros con los parasitos netnatodos Trichostrongylus axei y Ostertagia ostertagi (Ross et al.) ResUtnen. Fueron infectados terneros libres de panisitos, a 6-8 semanas de edad, con 150.000 larvas de T. axei 0 con 150.000 larvas de O. ostertagi, de tercer estadio, 0 bien combinaciones a tiempos varios de 100.000 larvas de T. axei Y 50.000 larvas de O. ostertagi, de tercer estadio.
En todos los animals se produjo grave diarrea entre la segunda Y la tercera semana de la infeccion, Y murieron 0 se llevaron in extremis a la matanza para la octava semana. Se describen la patologia clinica, la patologia gruesa y la histopatologia de las infecciones. Se observaron las diferencias en los niveles de pepsinogeno del suero despues de las diversas estructuras de la infeccion, siendo posible en la patologia gruesa distinguir claras lesiones resultantes de la diferencia en el porcentaje de infeccion de los dos parasitos.