The spread of Corynebacterium pseudotuberculosis infection to unvaccinated and vaccinated sheep

SUMMARY The decrease in the prevalence of Corynebacterium pseudotuberculosis after two generations of vaccination against the disease it causes, was used to estimate the rate of control of caseous lymphadenitis (CLA). Three groups of 150 sheep, of which 50 in each group were artificially infected with C pseudotuberculosis and 100 in each group were uninfected sheep, were run separately for 40 months and shorn 5 times to promote the spread of CLA. One lot of 50 infected sheep and 2 lots of 100 uninfected sheep were vaccinated against CLA. The rate of spread of CLA was recorded. Sheep vaccinated against CLA and naturally exposed to infection had a 74% lower infection rate than unvaccinated sheep. Sheep vaccinated against CLA and exposed to only vaccinated infected sheep had a 97% lower infection rate. Unvaccinated sheep had a 76% infection rate, with 77% of the transmission occurring at the 4th and 5th shearings, without any discharging CLA abscesses being observed. This study supports the view that in Australian wool producing flocks, CLA spreads mainly from sheep with discharging lung abscesses to sheep with shearing cuts. Vaccinated sheep infected with CLA have 96% fewer lung abscesses compared with unvaccinated infected sheep and are therefore less likely to spread this disease to other sheep .     

Epidemiological features of Morel's disease in goats

Morel's disease caused by Staphylococcus aureus subsp. anaerobius was diagnosed for the first time in Poland in October 2006 in a goat flock. A second infected flock was found two months later. The course of the disease in both flocks was observed for 15-17 months. Clinical manifestation was confined to abscesses located near major superficial lymph nodes, mostly: superficial cervical, subiliac, parotid and mandibular. At necropsy no other lesions were found. The incubation period was estimated at 3 weeks. Clinical signs were seen both in young and adult goats and up to 7 abscesses in one animal were noted. Abscesses tended to persist for 1 to 5 months, then rupture and heal completely. The initial high in-flock point prevalence in both flocks (93.6% and 84.4%) dropped to approximately 10-30% during next 3-4 months. Until the end of the observation period the in-flock point prevalence remained at this level and only single abscesses were observed, mainly in young animals. No influence of the concurrent caprine arthritis encephalitis virus (CAEV) infection on the clinical course of Morel's disease was noticed. It is to be concluded that the clinical course of Morel's disease in a goat flock resembles caseous lymphadenitis (CLA). However, in Morel's disease abscesses occur more frequently in young goats and are located near, not inside, the lymph nodes, as in the case with CLA. Also, the incubation period of Morel's disease seems to be shorter (3 weeks versus 2-6 months in CLA).     

A serological investigation of caseous lymphadenitis in four flocks of sheep

A double antibody sandwich ELISA developed by ID-DLO, Lelystad to detect Corynebacterium pseudotuberculosis infection was used on 329 sheep from four pedigree Suffolk flocks in which clinical cases of caseous lymphadenitis (CLA) had occurred. At subsequent necropsy, typical CLA lesions were seen in 133 sheep, and the diagnosis was confirmed on culture. Lesions were most commonly seen in lungs (n = 46), parotid lymph nodes (n = 44), prescapular lymph nodes (n = 38) and mediastinal lymph nodes (n = 31). The sensitivity of the ELISA test for detecting culture-positive sheep was 0.88, while the specificity of the test was 0.55. The antibody ELISA detected 87.5 per cent of sheep that had CLA lesions restricted to internal organs only. It was concluded that the ELISA test has a valuable role in detecting sheep with both clinical and subclinical CLA.     

The role of Corynebacterium pseudotuberculosis lung lesions in the transmission of this bacterium to other sheep

SUMMARY: :Five groups of 5 shorn and 5 unshorn caseous lymphadenitis (CLA)-free Merino wether weaners were each placed in feedlot pens with 6 Merino ewes, 2 or more of which had CLA lung lesions but no discharging superficial lesions. The sheep were kept together for 5 months.
Twenty-eight per cent of the shorn weaners and 20% of the unshorn weaners developed antibodies to Corynebacterium pseudotuberculosis. At slaughter, 8% of the shorn weaners and 12% of the unshorn weaners had CLA lesions in either lungs, lymph nodes or both. In the absence of contact with CLA-infected ewes, a control group of 5 shorn and 5 unshorn weaners failed to develop antibodies to C. pseudotuberculosis or CLA lesions in the same period. This showed that sheep with CLA abscesses in the lungs but no discharging superficial abscesses were a source of C. pseudotuberculosis infection to other sheep. Aust Vet J. 64: 261–263     

Effects of housing on the incidence of visna/maedi virus infection in sheep flocks

The incidence of seroconversion to visna/maedi virus (VMV) infection and its relationship with management and sheep building structure was investigated in 15 dairy sheep flocks in Spain during 3–7 years. Incidence rates were 0.09 per sheep-year at risk in semi-intensive Latxa flocks and 0.44 per sheep-year at risk in intensive Assaf flocks and was greatest for the one year old Assaf replacement flock. Separate multivariable models developed for replacement and adult flocks indicated that in both cases seroconversion was strongly associated to direct contact exposure to infected sheep and to being born to a seropositive dam. The latter effect was independent of the mode of rearing preweaning and the risk of seroconversion was similar for sheep fed colostrum and milk from a seropositive or a seronegative dam. These results are further evidence of the efficiency of horizontal VMV transmission by close contact between sheep and also suggest a inheritable component of susceptibility and resistance to infection. In contrast, indirect aerogenous contact with seropositive sheep was not associated with seroconversion as evidenced in replacement sheep housed in separate pens in the same building as adult infected sheep for one year. Consequently, VMV may not be efficiently airborne over short distances and this is important for control of infection. Moreover, there was no relationship between seroconversion and shed open areas. The latter could be related to having examined few flocks in which high infection prevalence dominated the transmission process while ventilation, may depend on a variety of unrecorded factors whose relationship to infection needs to be further investigated.     

Toxoplasmosis in Sheep: Epidemiological Studies in Flocks with Reproductive Loss from Toxoplasmosis

The epidemiology of toxoplasmosis was studied in 51 flocks with reproductive loss from the infection. Overt toxoplasmosis was diagnosed on 2–4 neighbouring farms on 6 occasions, involving a total of 15 flocks. In 14 of the 51 flocks the frequency of abortion was highest in a definite part or age group of the flock.Evidence was found that the source of infection may be confined to a particular part of an area or of a farm. There was apparently no transmission of Toxoplasma gondii from sheep with overt or latent toxoplasmosis to susceptible sheep. There were good reasons to believe that the parasite might have been transmitted via the silage in 1 of the flocks.     

Epizootiological survey of parainfluenza-3, reovirus-3, respiratory syncytial and infectious bovine rhinotracheitis viral antibodies in sheep and goat flocks in Quebec.

A serological survey was conducted in an attempt to detect antibodies against bovine respiratory viruses in sheep and goats from seven geographical areas of Quebec. Sera from 10% of the animals in 182 sheep flocks and 40 goat flocks were collected and specific antibodies against parainfluenza-3, reovirus type 3, respiratory syncytial and infectious bovine rhinotracheitis viruses were detected by hemagglutination-inhibition tests for the former viruses and complement fixation and seroneutralization assays for the latter viruses. Results showed prevalence rates of serological reaction to parainfluenza-3, reovirus type 3 and respiratory syncytial viruses of 28, 72 and 35% in sheep and 26, 64 and 36% in goats, respectively. No antibodies in infectious bovine rhinotracheitis virus were detected in sheep or goats tested. Prevalence rates varied according to the geographical area. No relationships were detected between age, sex, breed, size of flock and prevalence rates of different antibodies except that parainfluenza-3 antibodies were more common in large goat flocks and in sheep flocks with total confinement housing. A relationship between presence of clinical signs in the flocks and prevalence rates of antibodies was only demonstrated for parainfluenza-3 infection in goat flocks.     

Performance of a whole blood interferon-gamma assay for detection and eradication of caseous lymphadenitis in sheep

Caseous lymphadenitis (CLA), a chronic bacterial disease of sheep and goats caused by Corynebacterium pseudotuberculosis, could be controlled by eradication of infected carriers. This study aimed at validation of a whole blood interferon-gamma (IFN-gamma) enzyme immunoassay (EIA) (Bovigam, Pfizer) in naturally infected sheep for use in eradication of infection from a flock. This assay used formalin-inactivated whole bacterial cells as antigen. The sensitivity of the whole cell assay was improved by increasing both the volume of blood and the number of bacterial cells. The assay was validated in experimentally infected sheep and in a flock of known-negative sheep, as well as in a naturally infected flock, a proportion of which was vaccinated with a commercial CLA vaccine. An optical density (540nm) (OD) cut-off of 0.09 was effective in classifying animals as test positive or negative in the naturally infected flock, although there was variation in OD between visits, notably with weakly reacting animals. The test had a sensitivity of 91% and a specificity of 98%. Postmortem data supported the results in test-negative animals. Visit-to-visit variation in IFN-gamma EIA OD in the naturally infected flock as well as CLA disease status was used to develop an algorithm for the eradication of CLA from a known infected flock. The whole blood IFN-gamma assay shows promise for eradication of caseous lymphadenitis from sheep flocks.     

Epidemiological study on Mycoplasma synoviae infection in layers

Mycoplasma synoviae infection occurs worldwide in commercial poultry flocks and may result in severe economic losses. The prevalence of this mycoplasma in standard layers older than 60 weeks was studied in a French department and the characteristics of infected or free flocks were compared. The genomic profiles of isolates from 36 infected flocks were studied by pulsed-field gel electrophoresis and random amplified polymorphic DNA methods in order to investigate possible routes of transmission. The minimum inhibitory concentrations of antibiotics were determined. Results showed that infection was more frequent in multi-age farms. Egg production and mortality of infected flocks were respectively lower and higher than in non-infected flocks but the differences were not statistically significant. The genomic profiles of isolates were quite homogeneous, a feature which does not facilitate the understanding of routes of transmission. All isolates were susceptible to tetracyclines, macrolides (except erythromycin), spectinomycin and fluoroquinolones.     

The effect of antibody to caseous lymphadenitis in ewes on the efficacy of vaccination in lambs

The effect of maternal antibody to the toxin of Corynebacterium pseudotuberculosis, produced by caseous lymphadenitis (CLA) in ewes or by vaccinating ewes before lambing, on the efficacy of vaccination against CLA in their lambs was examined. Lambs were allocated to treatments according to either the vaccination history of their dam or level of CLA toxin antibody of their dam. They were vaccinated twice using 2 different inoculation regimes and then artificially infected with CLA organisms. The number of lambs with CLA lesions was assessed at slaughter. In one experiment high levels of CLA toxin antibody activity in ewes were associated with decreased efficacy of CLA vaccination in their lambs, when lambs were vaccinated at 2 and 8 weeks or 8 and 14 weeks of age. In a second experiment the efficacy of lamb vaccination at 8 and 12 weeks, but not at 14 and 18 weeks of age, was decreased. In sheep flocks with a high prevalence of CLA, vaccinating lambs against CLA at less than 10 weeks of age may not produce optimum protection against CLA in lambs. There was no difference in infection rate between lambs from vaccinated and unvaccinated ewes. However, vaccination of lambs at 2 and 8 wks was less effective that vaccination at 8 and 14 weeks, probably due to reduced immunocompetence in young lambs. In sheep flocks where significant numbers of lambs receive their primary vaccination at less than 3 weeks of age vaccination programmes to control CLA in lambs may be less effective.     

The association of sub-clinical paratuberculosis with the fertility of Greek dairy ewes and goats varies with parity

Our cross-sectional study investigated the association of sub-clinical Mycobacterium avium subsp. paratuberculosis (MAP) infection with failing to produce a live offspring the season of lambing/kidding (November 2001 to January 2002) before testing (in April-May 2002), in four dairy-sheep and/or goat flocks in Greece (369 animals >or=1.5-year-old). From each selected animal 10 ml of blood and 10 g of feces from the rectum were obtained. The harvested sera were tested for antibodies to MAP with a commercial ELISA test kit; the feces were cultured on Herrold's egg-yolk medium supplemented with mycobactin J and antibiotics. An animal was considered sub-clinically infected when found either seropositive or culture positive. The true prevalence of sub-clinically infected animals, adjusted for the sensitivity and specificity of the parallel testing, was 14% (0.1-28%) and 35.9% (9.2-62.7%) in sheep and goats, respectively. The association of fertility of sheep and goats with sub-clinical paratuberculosis was investigated in random-effects logistic models. Sub-clinically infected animals (compared to uninfected) had OR for live offspring the previous year of 5.4 for parity <4, OR=0.05 for parity >6, and a non-significant OR for the middle parity category.     

Prevalence of caseous lymphadenitis and usage of caseous lymphadenitis vaccines in sheep flocks

OBJECTIVE: To estimate the prevalence of caseous lymphadenitis (CLA), determine the current usage of vaccines against CLA and to measure the effectiveness of these vaccines on sheep farms. DESIGN AND POPULATION: A survey was undertaken on 223 sheep flocks in New South Wales, Victoria and Western Australia. METHOD: The prevalence of CLA was measured by conventional inspection techniques at abattoirs in lines of sheep that could be traced back to a farm. Managers of the flocks were sent a questionnaire about their vaccine practices, management practices and knowledge of CLA. RESULTS: The average prevalence of CLA in adult sheep in these flocks was 26% and varied from 20% in Western Australia to 29% in New South Wales. About 43% of sheep producers used CLA vaccines; only 12% used them as recommended. Awareness of CLA was highest in Western Australia. More producers would use CLA vaccine if they knew the prevalence of CLA in their flock and producers obtained most information about CLA from vaccine resellers. CONCLUSIONS: Only 10 to 15% of producers are currently achieving effective CLA control through the use of recommended CLA vaccination programs. In Western Australian flocks more than 25% of effectively vaccinated ewes will be sent to abattoirs in the 2 to 3 years after this study. However, large decreases in the prevalence of CLA can be achieved by about 70% of producers by either making adjustments to their vaccination programs or buying a vaccine with a CLA component. Two or three key facts on effective CLA vaccination could be made available at the point of sale of vaccines and from abattoirs that reported the prevalence of CLA to farmers.     

Post-shearing management affects the seroincidence of Corynebacterium pseudotuberculosis infection in sheep flocks

Associations between the incidence of caseous lymphadenitis (CLA) in sheep and post-shearing management and environmental factors were examined in a prospective study. CLA incidence was measured in 126 groups of 1- and 2-year-old sheep in 70 Western Australian flocks selected from the prevalence of cull-for-age ewes with CLA lesions at abattoirs. CLA incidence was assessed using a CLA toxin ELISA. Dichotomous and polychotomous stepwise logistic regression methods were compared in examining the effects of management and environment on CLA incidence. Shower dipping sheep for ectoparasite control after shearing increased the odds of high CLA incidence by five to six times and keeping sheep under cover for 1 h or more after shearing increased the odds of being in high CLA incidence categories three-fold. The seroprevalence of existing CLA infection within each age group affected incidence more than did the overall slaughter-based flock estimate. This suggests that CLA spreads mostly within groups of sheep shorn together.     

Serum antibodies to bovine coronavirus in Swedish sheep.

Altogether 218 sheep sera from 40 flocks in different parts of Sweden were screened for antibodies to bovine coronavirus (BCV). Nineteen per cent of the sera were positive and there was a significantly higher frequency (p < 0.05) of at least one positive sample in flocks with more than 100 adult sheep than in smaller flocks. There was also a significantly higher frequency (p < 0.001) of positive samples from sheep older than 4 years than from younger ones. Only a weak relationship between BCV positivity (2 or more positive samples, p < 0.05) and cattle contact was demonstrated in this study. Possible transmission routes and other factors that could have affected the result are discussed. In light of our finding that all 5 sheep experimentally exposed to BCV through contact with infectious cow faeces seroconverted, we conclude that the antibodies found in Swedish sheep are probably the result of BCV infections directly or indirectly transmitted from cattle.     

Transmission and control implications of seroconversion to Maedi-Visna virus in Basque dairy-sheep flocks

A retrospective analysis of seroconversion to Maedi-Visna virus (MVV) was carried out for 10 infected semi-intensively reared dairy-sheep flocks that were tested annually between 1994 and 1999. Four of the flocks raised replacement lambs artificially with bovine colostrum and milk replacement to avoid lactogenic MVV infection but did not prevent aerosol contact between replacements and other sheep in the flock. Flock culling percentages ranged between 14 and 25% and in eight flocks the number of sheep that seroconverted was similar to or lower than the number of sheep culled—suggesting that incidence could be reduced by culling seropositive sheep without increasing average culling percentages. Random-effects logistic regression indicated that seroconversion was associated positively with increasing contact with infected sheep and with lifetime MV-serological status of the dam (used as a proxy measure of genetic susceptibility), but not with mode of rearing pre-weaning (artificially or with a seropositive or seronegative dam). Our results indicate that when conditions allow efficient horizontal transmission, there is no evidence that lactogenic infection increases the risk of MV infection and that there is an important inheritable component of disease resistance or susceptibility.     

Assessment of the genetic risk and impact of lateral transmission in a valine-associated scrapie outbreak in sheep

OBJECTIVE: To characterize an outbreak of valine-associated scrapie, assess the relative risk of scrapie infection in relation to allele frequency at codon 136, and investigate lateral transmission of infection in a sheep flock within the United States. ANIMALS: 1,006 sheep. PROCEDURE: To determine genotypes, blood or semen samples were assessed via commercial testing; in 190 slaughtered sheep, scrapie status was determined via immunohistochemical evaluation of tissues. Scrapie-positive sheep born to scrapie-negative dams and sheep infected after 1 year of age were identified to assess lateral transmission. RESULTS: Genotypes were determined for codon 171 (164 sheep) or codons 136 and 171 (842 sheep). Forty-four of 160 slaughtered sheep of known genotype were scrapie positive. In these sheep, the presence of at least 1 valine allele at codon 136 (V136) was highly correlated with scrapie-positive status. Lateral transmission was the probable source of infection for 4 scrapie-positive sheep born to scrapie-negative dams and for 11 sheep in which scrapie was diagnosed at > 50 months of age. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the outbreak of scrapie was associated with a relatively high frequency of V136 in the flock, introduction of a valine-dependent scrapie strain, and the occurrence of lateral transmission. Genotyping of sheep may assist management decisions following diagnosis of scrapie in a sheep with at least 1 V136. It may be prudent to remove sheep of the diploid genotype AVQR (at codons 136 and 171) from infected flocks.     

Monte Carlo simulation of surveillance strategies for scrapie in Norwegian sheep

Our aim was to compare the efficiency of different surveillance strategies for detecting scrapie-infected sheep flocks in the Norwegian population using simulation modelling.The dynamic Monte Carlo simulation model has the flock as the unit. The input parameters include properties of the sheep population (number of flocks, flock size, age distribution, reasons for culling, breeds, prion protein-allele distribution); properties of scrapie (genotype-dependent infection rate and incubation periods, and age- and genotype-dependent prevalence of scrapie); properties of the surveillance strategy (selection of sheep for examination, period in which infected sheep are detectable, and properties of the diagnostic tests). For simplification, the prion protein-alleles were grouped into three allele groups: VRQ, ARR, and ARQ' (ARQ' represents ARQ, ARH and AHQ).Through either abattoir surveillance or surveillance of fallen stock, 70% of the detected sheep (compared to 33% in the underlying population). The model output was sensitive to the susceptibility of infection for the genotype ARQ'/ARQ'. The effect was large for abattoir surveillance (increased susceptibility increased the efficiency of abattoir surveillance).     

Reaction of goats to infection with infectious bovine rhinotracheitis virus

Intranasal exposure of goats to infectious bovine rhinotracheitis virus resulted in mild respiratory disease and virus reisolation from nasal secretions. No disease was produced in goats exposed to the same virus by the genital or ocular routes. There was serological evidence of contact transmission of infection from infected goats to cattle. Virus recrudescence was not detected in goats treated with dexamethasone two months after virus inoculation.     

Pseudotuber culosis in man: Possible epidemiological role of the cats

Human infection by Malassez and Vignal's bacillus (Yersinia pseudotuberculosis) can take many clinical aspects, the most frequent of which is mesenteric adenitis with pseudo-appendicular syndrome, but occasionally also appearing as a tumor of the right lower abdominal quadrant.

In a subsequent stage this mesenteric adenitis is often accompanied by erythema nodosum. There also exist some septicemia-like forms, which have become more and more frequent of late, always appearing on a particular terrain (predisposed persons).

These various forms all correspond to contamination via the digestive route. Other, more exceptional modes of contamination may result in much rarer forms, such as ocular or pulmonary forms.

Diagnosis is based on: (a) demonstrating the presence of Yersinia pseudotuberculosis, (b) serodiagnosis, (c) a positive intradermal reaction, (d) the characteristic aspect of lymph node lesions.

Pseudotuberculosis is extremely frequent in animals. Many species, most of them rodents or birds, can serve as healthy carriers. This is how cats, through their access to this natural “reservoir”, get contaminated and thus act as a “conveyor belt” in transmitting the disease to man.     

Introduction and spread of thermophilic campylobacters in broiler flocks.

Campylobacteriosis is the most commonly reported infectious cause of human gastroenteritis in developed countries and broiler chickens are considered to be the major food-borne source of the infection. The control of the infection in man depends upon its control in broiler flocks but the epidemiology in poultry is poorly understood. Up to 50 per cent of broiler flocks may be infected and most of the birds in an infected flock carry the organisms until slaughter. Vertical transmission through the egg appears unlikely but there are many other potential sources of the infection for the chicks; direct contact with infected animals or birds has been proposed and there is also evidence for indirect transmission through drinking water or insect vectors. It is suggested that the cross-sectional studies discussed in this review should be followed by well designed case-control studies to test the aetiological hypotheses put forward.