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CAE - Caprin artritt-encefalitt virusinfeksjon hos geit

Disease Recordings in a Goat Herd before and after Control of Caprine Arthritis-Encephalitis Virus and Corynebacterium pseudotuberculosis Infection. K. Nord1)* and L.O. Eik2)

Summary

Disease registrations in a goat herd before and after the implementation of a control programme for caprine arthritis-encephalitis virus and Corynebacterium pseudotuberculosis infection revealed a great improvement in the health of the herd as a result of the scheme, apart from a high incidence of mastitis in both the infected and seronegative groups. CAE, caseous lymphadenitis, ectoparasites and respiratory infections were not observed in the seronegative group, and birth weights of kids were increased.

Key words

Goat: Caprine arthritis-encephalitis virus; Corynebacterium pseudotuberculosis; Control;

Clinical findings; Pathological findings; Birth weights

Introduction

Like other lentiviruses, caprine arthritis-encephalitis virus (CAEV) causes persistent infection, although most CAEV-infected goats remain clinically healthy. Signs of disease are associated with progressive inflammation in one or more organ or tissue systems such as joints, bursae, brain, spinal cord, lungs and udder (Bulgin 1990; Dawson 1987). While some studies indicate that increased culling may be necessary and that birth weights may fall (Greenwood 1995; Mockenhaupt & Bauer 1987), other studies have failed to reveal any differences in body condition between antibody positive and negative goats (Elliot & Mason 1985).

Signs of caseous lymphadenitis (CLA). caused by Corynebacterium pseudotuberculosis (C. pseudotuberculosis), include suppurative inflammation in one or more lymph nodes (Brown & Olander 1987). In cases with systemic involvement, chronic pneumonia, pyelonephritis, ataxia and chronic wasting may be present (Blood 1989).

A control programme was designed to eliminate both infections, and is described in detail in another report (Nord et al., to be published). The main purpose of this study was to compare clinicopathological findings and birth weights to obtain an indication of the overall health benefits gained by the introduction of the rather strict control measures.

Materials and methods

Animals and herd management The selected dairy goat herd comprised 113 goats of the Norwegian breed. Animals above six months of age were defined as adults. In 1992, all adult goats were examined for antibodies against CAEV and C. pseudotuberculosis. All goats were regarded as infected, and were slaughtered two years after implementing the control programme. In the control scheme, which was established in 1993, kids were removed from the infected goats at birth, avoiding any contact between dam and kid. The kids were fed cow's colostrum and milk and kept completely segregated from the infected group. A seronegative group was established, based on the removed kids and their offspring. Goats in the seronegative group were allowed to kid naturally and to mother their kids. The kids were tested for antibodies against CAEV before their 14th day of life, and thereafter every sixth month (Nord et al., to be published). Animals with positive or indeterminate CAEV-antibody test results were culled. All goats were tested for antibodies against C. pseudotuberculosis 1ree times during 1995, the third year of the control programme (Nord et al, to be published).

A group of 29 kids (Group A) which were born in 1993 and raised according to the control scheme was selected for closer study, as was another group of nine kids (Group B) which were born in 1995 and mothered by their seronegative dams

In 1993, a group of 29 kids (Group C), not included in the control scheme, was exposed to CAEV and CLA by being nursed within the infected herd by their seropositive dams.

Clinicopathological examination

Animals were routinely observed for clinical signs each day. Birth weights were recorded for 33 kids born in 1995 of 23 seronegative dams, and for 25 of the kids in Group C representing 18 seropositive dams. The animals were examined more closely clinically at four to six months of age, and thereafter twice a year, including general assessment of condition and gait, inspection and palpation of joints and udder, auscultation of the chest, and inspection and palpation for subcutaneous abscesses or enlargement of lymph nodes. Milk examination, including the bromthymol test, was carried out. Animals were otherwise clinically examined if signs of illness were observed. Cumulative incidences of clinical mastitis in the infected and the seronegative group were based on recordings of abnormalities of secretion, and in size, firmness and temperature of the mammary glands during one year, each affected animal only registered once.

All severely ill animals together with two clinically healthy adult goats from each group, as well as further 19 goats with moderate signs in the infected group, were killed andautopsied. Gross examination of the other goats in both groups was performed using routine procedures during the slaughtering process. Histopathological examination of affected organs was carried out on formalin-fixed, hematoxyline and eosine-stained sections.

The kids in Group A were examined post mortem (p.m.) only in case of severe illness.

The kids in Groups B and C were killed and examined p.m. at four to six months of age.

Laboratory examinations of milk

Milk samples were taken once, about six weeks after kidding, from all lactating goats in both the infected and the seronegative group for routine laboratory bacteriological mastitis diagnosis (Anonymus 1987, International Dairy Federation 1981). Schalm's Test indicating somatic cell count (Schalm et al. 1971) was performed on each milk sample. Diagnosis of bacterial mastitis was based on positive bacteriological findings combined with a Schalm's Test result of three or above (International Dairy Federation 1987).

Serological examinations

Sera were examined for antibodies against CAEV by an ELISA (Rimstad et al. 1994), and for antibodies against C. pseudotuberculosis using a haemolysis inhibition test (HIT) (Holstad 1986a) as described in more detail by Nord et al. (to be published).

Data analysis

The chi square test was used to examine the differences in cumulative incidences of clinical mastitis in the infected and seronegative group. Prevalences of bacterial mastitis about six weeks after kidding in infected and seronegative lactating goats aged two years or younger were compared using the Fisher exact test. Confidence intervals (95%) for relative risks (RR) were calculated in Epi Info, Version 6 (Dean 1994)

Mean birth weights and total birth weights (kg) of kids were compared between seropositive and seronegative dams using the Standard Least Squares Model in the JMP software (SAS 1995) for MS-Windows, controlling for parity (uniparous or multiparous), sex (male, female) and birth-type (single, twins, triplets).

Results

Clinicopathological findings

Clinical findings in adult goats in the infected group during the 1993 one-year period are summarised in Table I a.

table1

Signs consistent with CAE were found in altogether 46 cases, stiffness of gait, lameness, and swelling of joints and bursae, particularly in the carpal area, being predominant. Otherwise ataxia, progressive paresis, opisthotonus or head tilt also occurred. Subcutaneous abscesses or enlarged lymph nodes were found in 37 adults. Although frequently observed, sterile abscesses at or near to the site for vaccination against Mycobacterium pseudotuberculosis were not recorded (Holstad 1986b). Ectoparasites such as lice and keds were frequently observed in spite of regular injections of Ivermectin once a year during the dry period. Clinical mastitis was recorded in altogether 30 goats, of which eight were aged two years or younger.

Pathological diagnoses for 32 CAEV- and CLA-infected goats (Table 2) were in agreement with the clinical diagnoses.

table2

Affected periarticular tissues were thickened and fibrous. Cultures were made from abscesses or enlarged lymph nodes in 15 of the 32 affected animals, five yielding C. pseudotuberculosis and one Actinomyces pyogenes, while the remaining nine were negative. Of the seven goats showing respiratory signs, five had abscesses in the lungs, C. pseudotuberculosis being isolated in three cases, while the other two were bacteriologically negative. Pasteurella haemolytica was isolated from two animals without abscesses. Small fibrous nodules in the lung parenchyma, containing live or dead lung worms, were found in most animals.

Histological lesions in the goats which suffered from paresis consisted of multiple perivascular foci of lymphocytes and macrophages in the white matter of the brain and in the cervical and lumbosacral segments of the spinal cord. Examination of affected joints revealed hypertrophy of the synovial villi, sub-synovial mononuclear cell infiltration, hyperplasia, and focal areas of necrosis. The lungs of 22 of the 32 goats examined showed mononuclear cell infiltration and hyperplasia, septal fibrosis, alveolar epithelisation, and proteinaceous fluid in the alveolar lumina. A non-purulent mastitis was found histopathologically in eight of the 32 animals, manifesting itself as a diffuse accumulation of lymphocytes around ducts and within glandular interstitium, and an increase in connective tissue. All these histological lesions were consistent with CAE.

No CAE-like signs, abscesses due to C. pseudotuberculosis or respiratory signs were observed in the seronegative group (Table l b).

table1b

The five cases of arthritis registered developed during the first weeks of life, and bacteria were found in the synovia. No ectoparasites were found. Pathological diagnoses for the seronegative group are not given separately, as they hardly differed from the clinical diagnoses. Lung changes due to lung worms were rarely seen. However, altogether 15 goats died from diarrhoea, mainly due to coccidiosis and Clostridium species, while six died as the result of accidents or transportation stress. During one year, 22 cases of clinical mastitis were recorded (Table 1 b).

Cumulative incidences of mastitis calculated as relative risks were not found to differ between the infected and seronegative group: RR = 1.12 (0.59 < RR < 2.16), p = 0.7 Table 3.

table3

Differences in prevalences of bacterial mastitis between the infected and seronegative lactating goats were calculated for staphylococcal mastitis: RR = 1.84 (0.59 < RR < 5.72), p = 0.28, Table 4. and for mastitis with coagulase-negative Staphylococcus sp.: RR = 5.9 (0.56 < RR < 62.4), p = 0. 16. No statistically significant differences were found.

table4

In the kids exposed to CAEV and CLA (Group C), the predominent clinical and pathological findings were emaciation and impaired growth associated with a Mycoplasma-like bronchointerstitial pneumonia Table 5a.

table5a

In only three out of 26 kids was purulent pneumonia involving Pasteurella haemolytica infection found. One out of seven females had a non-purulent, CAE-like mastitis (Table 5a). Three kids died before the end of the study period. Two of these developed septicaemia, while the third developed progressive ataxia, opistothonus, head tilt and tremor at the age of about three and a half months. Although this kid was negative for antibodies against CAEV, it had a non-purulent myelitis of brain and spinal cord with multiple perivascular foci of lymphocytes and macrophages in the white matter. consistent with a diagnosis of CAE.

The kids in the seronegative group were predominantly clinically sound, Table 5b.

table5b

Three kids in Group A which had been fed pooled cow's colostrum died from haemolytic anaemia. Necropsy revealed no pathological lesions in any of the kids in Group B.

The mean birth weight of kids from seropositive goats (3.1 kg) was lower than that of kids from seronegative goats (3.5 kg), When correcting for the effect of parity, sex and birth-type by using least squares means, the birth weights were 3.2 kg and 3.6 kg, respectively, revealing statistically significant differences (p = 0.003), Table 6.

table6

A similar statistical analysis for total birth weights per dam revealed similar significant differences, seropositive goats having lower least squares mean of total birth weight (3.0 kg) than seronegative goats (3.7 kg) (p--0.0008) (Table 6).

Serological findings

Before the control programme was introduced, the herd prevalences of antibodies against CAEV and C. pseudotuberculosis were 97% and 94%, respectively. Of 229 goats examined for antibodies against CAEV over a three-Year period with the control programme in operation, altogether six were seropositive, while for ten the result was indeterminate (Nord et al, to be pub].). All goats were negative for antibodies against C. pseudotuberculosis.

Of the 38 kids in Groups A and B which were raised according to the control scheme, one was positive for antibodies against CAEV before the 14th day of life, and was culled. The others were seronegative.

Of 26 kids in Group C which were nursed by infected dams, 19 had antibodies against CAEV and seven had indeterminate results at the age of four to six months.

Discussion

As suggested by the clinical and pathological findings, CAE was recorded as a disease problem in the infected herd, causing premature culling and several cases of arthritis. In the control programme group, no signs of CAE were registered. The few cases of arthritis found in the seronegative group were all found to be due to bacteria. Likewise, CLA was common in the infected herd, causing disease and condemnation of meat. In the seronegative group, the absence of signs of CLA was in agreement with the serological findings.

The incidence of adult goats suffering from pneumonia was reduced from about 18% to 0. This may have been due not only to the absence of CAE and CLA, but partly also to increased resistance to other diseases. Nevertheless, the absence or decrease in incidence of other diseases was probably mainly due to the eradication or reduction of pathogenic organisms in consequence of the control programme. The high incidence of ectoparasites in the infected goats might have been due to inadequate treatment, as Ivermectin was injected only once a year. The eradication of ectoparasites in the seronegative goats was also most likely a result of the control programme. Similarly, lung worms were found in most of the adult goats in the original herd, but only in a few cases in the seronegative group. This might partly have been due to the use of different pastures before and during the control programme.

The non-purulent inflammatory changes in the udders might have been partly caused by CAEV, especially when they occurred in young infected kids or in nulliparous goats.

However, the incidence of acute and chronic mastitis did not decrease as a result of the control programme, and was most likely influenced by the poor milking procedures registered in the herd. Factors predisposing to mastitis might disguise any possible effect of CAEV-infection.

The major health problem in young kids prior to the introduction of the control programme was pneumonia. Lung lesions found at p.m. were similar to those caused by infection with Mycoplasma sp. However, as culture and serologic testing for Mycoplasma sp. was not available, this diagnosis was not confirmed. Nevertheless, the control programme seemed to have cleared the herd of this respiratory infection. In young kids, the incidence of respiratory signs and pulmonary lesions was reduced from about 100% to 0.

The most practical and safe source of immunoglobulins was considered to be cow's colostrum (Bertolini 1995; Ellis et a]. 1983). However, three kids which were fed pooled cow's colostrum died from anaemia at about one week of age. Some cows produce colostrum containing antibodies against kids' erythrocytes, inducing haemolysis (Winter & Clarkson 1992). As the risk of the presence of such antibodies is greater in pooled cow's milk, feeding routines were changed to feeding milk from one cow at a time, male kids being test-fed beforehand. No further deaths from anaemia subsequently occurred.

Statistical analyses revealed significantly increased mean birth weights and total birth weights in seronegative goats, as found by (Greenwood 1995) for CAEV-antibody negative animals. As birth weights were compared for different years, differences might be influenced by heredity, feeding, management, age at parturition, and time of birth. Differences in birth weights might also have been caused by the overall health benefits, as other diseases were eradicated as well. Nevertheless, the increased birth weights seemed to some extent to be due to the strict eradication programme.

When designing a programme to control CAEV-infection, there seem to be considerable health benefits to be gained if the program also includes the control of other infectious diseases. As horizontal transmission of the virus seems to be of more importance than previously assumed (Adams et al. 1983; Rowe et al. 1992; Nord, to be published), a rather strict control programme is probably necessary anyway to ensure eradication of the CAEV-infection. The incorporation of other important infections such as caseous lymphadenitis and respiratory infections seems to be possible without much extra burden.

Acknowledgements

Our sincere thanks go to A.Valle and K. Eikanger, Department of Animal Science, Agricultural University of Norway, for providing assistance and performing health recordings. We are grateful to Dr. G. Gunnes, Department of Pathology, Norwegian College of Veterinary Medicine, for pathological examinations. Thanks are also due to dr. G. Holstad, National Veterinary Institute. Norway, for clinical and serological examinations for C. pseudotuberculosis. to Dr. A. Storset, Norwegian College of Veterinary Medicine, for sampling the infected animals and to District Veterinary Officer LG. Nørstebø for clinical examinations and sampling. We are also grateful to Dr. R. Bjerke Larssen, Norwegian College of Veterinary Medicine, for assistance concerning statistical analyses, and to Dr. S. Waage, Central Veterinary laboratory, Norway, for performing examinations of milk.

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Sammendrag

Sykdomsregistreringer i en geitebesetning før og etter et bekjempelsesprogram for caprin artritt-encefalitt virus infeksjon og byllesjuke

Sykdomsregistreringer i en geitebesetning før og etter et bekjempelsesprogram for caprin artritt-encefalitt virus infeksjon og byllesjuke viste store generelle helseforbedringer som et resultat av opplegget, bortsett fra høy prevalens og kumulativ insidens av mastitt både i den infiserte og seronegative flokken. CAE, byllesjuke, ektoparasitter og smittsomme respirasjonslidelser ble ikke påvist i den seronegative flokken. Fødselsvektene hos kje var høyere etter bekjempelsen.

1)Norwegian College of Veterinary Medicine, Department of Large Animal Clinical Sciences, P.O.Box 8146 Dep., N 0033 Oslo, Norway

2)Agricultural University of Norway, Department of Animal Science, P.O. Box 5025, N 1432 Aas, Norway

*Corresponding author