Epizootiology of rotavirus diarrhoea in the bovine species*

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1 Rev. sci. tech. Off. int. Epiz., 1984, 3 (4), Epizootiology of rotavirus diarrhoea in the bovine species* P.-P. PASTORET**, A. SCHWERS**, C. VANDEN BROECKE***, and J. WÉRENNE*** Summary: Contamination of calves by rotavirus occurs soon after birth. The main source of virus in the surroundings seems to be the faeces of diarrhoeic calves, but it has also been observed with a high frequency in stools of apparently healthy ones. Other animal species may play a role in the dissemination of bovine rotavirus: dogs and cats have been shown to multiply bovine rotavirus asymptomatically after experimental infection, and rotavirus, probably of bovine origin, has been isolated from stools of farm dogs; wild ruminants like the roe-deer also seem to play a role. Many factors affect the pathogenicity of rotavirus and influence the course of the disease: the strain, the dose of virus, the age of the calf at the time of contamination, eventual concomitant infections by other viruses or bacteria... The presence of circulating antibodies is not sufficient to prevent rotavirus diarrhoea in newborn calves: antibodies must be present in the intestinal lumen to protect the animal. Aspecific mechanisms like the production of endogenous interferon also appear to play an important role in the control of infection by the calf. Bovine rotavirus is ubiquitous, and the contamination of calves is impossible to avoid. Moreover, medical prophylaxis is not the definite solution. The main way to prevent diarrhoea is thus to help the calf to overcome the infection. For this purpose, bacterially produced interferon will probably be very useful. INTRODUCTION Rotavirus is one of the major causes of diarrhoea in calves (13, 17, 24, 26, 33). In Belgium, the virus is implicated in up to 30% of the cases of diarrhoea * Presented at the VII International Symposium of the W.A.V.M.I. held in Barcelona, Spain, October ** Department of Virology, Faculty of Veterinary Medicine, University of Liège, 45, rue des Vétérinaires, B-1070 Brussels, Belgium. *** Department of General Chemistry, Faculty of Sciences, Free University of Brussels, 50, avenue Franklin Roosevelt, B-1050 Brussels, Belgium.

2 844 in newborn calves (34, 35, Antoine, personal communication) and provokes important economic losses. It is, therefore, essential to know the mode of transmission of the virus, the way it persists in infected farms and the factors that may influence its pathogenicity. Sources of rotavirus in the surroundings. Rotavirus does not seem to cross the placental barrier (6, 8). This is not suprising since there is still no definite evidence that viraemia occurs after rotavirus infection (20, 59) and specific anti-rotavirus antibodies have never been detected in precolostral calf sera (6, 8), although the bovine foetus is perfectly able to produce an immune response against rotavirus antigens from the 127th day of its developement (39). Contamination of newborn calves occurs, therefore, very soon after birth, as in natural conditions rotavirus excretion has been observed within 48 hours after birth (25). Asymptomatic excretion of rotavirus by adult cows has been described (12, 30, 67), but remains uncommon and therefore does not seem to play a significant role in the dissemination of the virus (7). The main source of rotavirus in the surroundings seems to be the faeces of diarrhoeic calves, that contain large amounts of viral particles (7, 61, 66). Nevertheless, rotavirus has also been observed in the stools of apparently healthy calves (1, 7, 25, 38). In Belgium, using a counterimmunoelectroosmophoresis technique, up to 25 % of the healthy, six week to three month old calves from a selection station excreted rotavirus in their faeces (41), showing that asymptomatic excretion is a common event in older calves. This may be due either to prolonged asymptomatic viral multiplication, or to successive reinfections ; the second hypothesis is the more likely, as re-infection of dogs, cats or calves leads to re-excretion of rotavirus (42, 43, 49). Moreover, rotavirus is highly resistant and contamination through humans, contaminated material or infected areas certainly plays a role in the transmission of the infection (42, 66). Role of other animal species in the transmission of bovine rotavirus. Dogs and cats disseminate bovine rotavirus asymptomatically after experimental infection (42, 43). Viral excretion in these two species may exceed two weeks, and repeated inoculations lead to repeated virus multiplication (42, 43), despite the presence of specific antibodies in cats (43). Dog to dog, cat to cat and cat to dog transmission is effective (42, 43). Moreover, rotavirus, most probably of bovine origin, has been isolated from stools of farm dogs (18), showing that cross-contamination occurs in normal breeding conditions.

3 845 Because of their presence in most of the farms, often in close contact with calves, dogs and cats may play a role in the maintenance of rotavirus infection (44). Other wild ruminants such as the roe-deer (Capreolus capreolus) are frequently contaminated by rotavirus (47) and, being closely related to cattle, are probably able to carry bovine rotavirus. Factors affecting the pathogenicity of bovine rotavirus. Many authors described the existence of several bovine rotavirus strains, differing by their antigenic, biochemical or biological properties (5, 10, 16, 32, 36, 56, 63) and sometimes by their pathogenicity (3, 4, 5). The dose of virus is also an important factor: diarrhoea was observed in piglets only when the amount of rotavirus increased in the surroundings (22) and a dose effect was also suggested for calves (2, 61). Surprisingly, very high doses of cell-culture bovine rotavirus failed to reproduce diarrhoea in colostrumdeprived newborn calves, while lower doses succeeded (40, 45, 46): such paradoxical results could be explained by a phenomenon of interference (60). The age of the animal at the time of infection may play a role, as the susceptibility to rotavirus infection in newborn calves, lambs or piglets decreases as the animal becomes older (2, 21, 52). Differences also appear to exist between virus isolates in their ability to affect animals of different ages (2). The role of concomitant infections by other viruses, bacteria or other agents must also be considered: it is well known that the association between rotavirus and enteropathogenic Escherichia coli increases the pathogenicity of both agents (15, 27, 29, 54, 58). Control of viral multiplication in calves. The presence of circulating anti-rotavirus antibodies of colostral origin does not prevent rotavirus diarrhoea in newborn calves (28, 51): to protect the animal, antibodies must be present in the intestinal lumen (51, 54). This is not surprising since rotavirus multiplies only in the epithelial cells of the gut (24), and, therefore, escapes contact with circulating antibodies, which are thus unable to neutralize it. Actively acquired immunity, as demonstrated by seroconversion, is also not sufficient to protect calves againts reinfections (49). The percentage of animals possessing anti-rotavirus antibodies in a herd is an epidemiological indicator, depending upon management conditions, but is not directly related to the prevalence of calf diarrhoea in the farm (48).

4 846 A mechanism susceptible of playing an important role in the control of rotavirus multiplication is the endogenous interferon response (23, 45, 46). Bovine rotavirus seems to be very susceptible to interferon (11, 14). Newborn calves experimentally infected with bovine rotavirus produce high levels of interferon in the lumen of the gut (20), but also in their plasma (20, 60). In calves inoculated with high doses of bovine rotavirus, circulating interferon appeared very early and no diarrhoea was observed while, in calves inoculated with lower virus dose, interferon production was delayed and preceded by an episode of diarrhoea (60). DISCUSSION Calves are certainly the main source of rotavirus in the environment, but other species like dogs or cats may also play a role in the persistance of infection in a farm. The infection is ubiquitous, the virus fairly resistant and hygienic measures like isolation of the calves or spacing of births may decrease the pressure of infection (7), but are not sufficient to prevent contamination. Attempts to vaccinate have often been unsuccessful (13,2). Moreover, calves can be infected several times (49). Better results have been obtained by prolonged administration of colostrum to calves (51, 55), usually associated with vaccination of cows to obtain higher antibody levels in the colostrum and milk (31, 37, 53, 54, 62). It is, therefore, necessary to study how to help the calves to overcome infection (44). In the absence of drugs selectively active against rotavirus, the treatment of rotavirus diarrhoea remains symptomatic. Bismuth subsalicylate might, however, be useful as it has been shown to inhibit the multiplication of bovine rotavirus in cell cultures (9), and also to absorb the enterotoxin produced by enteropathogenic strains of Escherichia coli (19). In the near future, interferon or interferon inducers will be available. Indeed, human and bovine interferons are now produced by bacteria (64). New interferon inducers, efficient and devoid of toxicity, are also under study (57). Because of the susceptibility of bovine rotavirus to interferon, exogenous bovine or simian interferon, or inducers of endogenous interferon could be given to newborn calves to prevent the onset of diarrhoea (65). Exogenous human interferon has already succeeded in preventing experimental rotavirus diarrhoea in newborn calves (50).

5 847 ACKNOWLEDGEMENTS This work was supported by a grant from the "Institut pour l'encouragement de la Recherche Scientifique dans l'industrie et l'agriculture" (IRSIA). We wish to thank Mrs Maria Maenhoudt for her assistance. * * * EPIZOOTIOLOGIE DE LA DIARRHÉE À ROTAVIRUS CHEZ LES BOVINS. P.-P. Pastoret, A. Schwers, C. Vanden Broecke et J. Wérenne. Résumé : La contamination du veau par le rotavirus se produit le plus souvent dans les heures qui suivent la naissance. Les veaux atteints de diarrhée constituent la principale source de virus dans le milieu, mais des veaux apparemment sains peuvent également l'excréter. D'autres espèces animais jouent probablement un rôle non négligeable dans la dissémination du rotavirus bovin : le chien et le chat multiplient ce virus de manière asymptomatique après infection expérimentale, et du rotavirus vraisemblablement d'origine bovine a été isolé de matières fécales de chiens de ferme ; des ruminants sauvages comme le chevreuil pourraient également jouer un rôle de réservoir. Parmi les facteurs pouvant influencer la pathogénicité du virus, il faut citer la souche virale, la dose de virus, l'âge du veau lors de la contamination, l'infection concomitante par d'autres virus ou d'autres agents pathogènes... La présence d'anticorps circulants d'origine maternelle ne suffit pas à prévenir la diarrhée à rotavirus chez le veau nouveau-né : pour exercer leur effet protecteur, les anticorps doivent se trouver dans la lumière intestinale. Des mécanismes aspécifiques tels que la production d'interféron jouent un rôle important dans le contrôle de l'infection. Puisque le rotavirus bovin est ubiquiste et que la contamination du veau par ce virus semble inévitable, quelles que soient les mesures hygiéniques prises, et en l'absence de vaccins parfaitement efficaces, la lutte contre la diarrhée implique la recherche de moyens permettant d'aider le veau à surmonter l'infection. Il est possible que l'administration d'interféron exogène s'avère extrêmement utile. * * * EPIZOOTIOLOGIA DE LA DIARREA POR ROTAVIRUS EN LOS VACUNOS. P.-P. Pastoret, A. Schwers, C. Vanden Broecke y J. Wérenne. Resumen : Lo más a menudo, la contaminación del ternero por el rotavirus se produce en las horas que siguen al nacimiento. Los terneros atacados de diarrea constituyen la principal fuente de virus en el media, aunque también pueden excretarle terneros aparentemente sanos.

6 848 Probablemente otras especies animales tienen un papel no desestimable en la diseminación del rotavirus bovino : el perro y el gato multiplican el virus de modo asintomático tras la infección experimental ; también se ha aislado rotavirus posiblemente de origen bovino en materias fecales de granja ; asimismo, puden desempeñar un papel de reservorio rumiantes salvajes como el corzo. Entre los factores que pueden influir en la patogenicidad del virus, hay que citar la cepa vírica, la dosis de virus, la edad del ternero en el momento de la contaminación, la infección concomitante por otros virus u otros agentes patógenos. La presencia de anticuerpos circulantes de origen materno no basta para prevenir la diarrea por rotavirus en el ternero recién nacido : para que ejerzan un efecto protector, los anticuerpos deben estar en la luz intestinal. Mecanismos específicos tales como la producción de interferón desempeñan un considerable papel en el control de la infección. Por cuanto el virus bovino es ubiquitario y parece inevitable la contaminación del ternero por el virus, cualesquiera que sean las medidas higiénicas que se adopten, y al no haber vacunas perfectamente eficaces, la lucha contra la diarrea implica la indagación de medios para ayudar al ternero a vencer la infección. Posiblemente resulte de gran utilidad la administración de interferón exógeno. REFERENCES * * * 1. BEGIN M.E., DEA S, DAGENAIS L. and ROY R.S. (1979). Comparison of electron microscopy, counterimmunoelectroosmophoresis and virus isolation in cell culture for the detection of bovine rotavirus. Proc. 2nd Int. Symp. on Neonatal Diarrhea, Saskatoon, Canada, Oct. 2-5, (1978), BRIDGER J.C. (1980). Rotavirus: the present situation in farm animals. Vet. Annu., 20, CARPIO M., BELLAMY J.E.C. and BABIUK L.A. (1981). Comparative virulence of different bovine rotavirus isolates. Can. J. Comp. Med., 45, CASTRUCCIG., FERRARI M., FRIGERI F., CILLI V., DONELLI G., ANGELILLO G. and BRUGGI M. (1983 a). A study of cytopathic rotavirus strains isolated from calves with acute enteritis. Comp. Immunol. Microbiol, infect. Dis., 6, CASTRUCCI G., FERRARI M., FRIGERI F., CILLI V., CALEFFI F., ALDROVANDI V., RAMPICHINI L. and TANGUCCI F. (1983 b). Experimental infection and cross protection tests in calves with cytopathic strains of bovine rotavirus. Comp. Immunol. Microbiol. infect. Dis., 6, DAGENAIS L., LANSIVAL B., PASTORET P.-P., MASSIP A. and KAECKENBEECK A. (1980 a). Absence de rotavirus dans le meconium de veaux. Ann. Méd. Vét., 124, 303.

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