Application of different methods for the diagnosis of paratuberculosis in a dairy cattle herd in Argentina

Paratuberculosis (Ptbc) has a high prevalence in Argentina, that affects dairy and beef cattle. The culture is the gold standard to the diagnosis of the disease. Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis), the aetiological agent, is difficult to isolate and grow in culture. In this study, 24 randomly selected cows of the Fresian breed from a dairy herd with a history of Ptbc were used to evaluate the performance of different diagnostic techniques. These animals did not show clinical signs of the disease. However, another animal from this herd presented evidence of clinical disease at the moment of the present study. This animal was necropsied and one strain of M. paratuberculosis was isolated from faeces, lymph nodes and intestine. Serum for indirect absorbed enzyme-linked immunosorbent assay (ELISA) and agar gel immunodiffusion (AGID) tests and whole blood samples to perform gamma interferon (gammaIFN) release assays were obtained from each animal. Faeces and milk samples to carry out bacteriological cultures, PCR identification of M. paratuberculosis, and direct examinations of smears with Ziehl-Neelsen's (ZN) stain were also collected. Tuberculin test with bovine purified protein derivative (PPD) in the caudal fold was performed. The results showed that 10 out of 24 animals (41.6%) were positive to ELISA. Eight strains of M. paratuberculosis were isolated, six from faeces, two from milk. Five of the animals that excreted the bacteria through faeces were ELISA-positive, whereas the excreters through milk were negative to ELISA. No positive samples by AGID were obtained in clinical asymptomatic animals. Seven samples gave positive gammaIFN results with avian PPD, but only two of these animals were confirmed with culture. Direct PCR, to detect IS900 (M. paratuberculosis) in faeces and milk samples, was negative, but PCR using material taken from faecal and milk cultures gave positive results before visualizing the colonies. No sample was positive by PCR directed to IS6110 (M. tuberculosis complex). There was not always agreement between isolations and ZN in the studied samples. In conclusion, the absorbed ELISA was useful to detect positive animals and excreters through faeces but not through milk. PCR applied to cultures with incipient development before the visualization of colonies was effective to specifically determine the presence of M. paratuberculosis. The gammaIFN test was not able to detect the most positive animals confirmed by culture. The importance of using ELISA and cultures is emphasized by this study but it is necessary to continue with the gammaIFN test development for early detection of the disease.     

Modelling of prevalence development in a paratuberculosis control program in a dairy herd

A modelling approach to calculate the success of a paratuberculosis control programme in dairy herds is presented. The essential parameters of the model are the prevalence at the beginning of the programme, diagnostic sensitivity and specificity of the tests used, discipline in culling test-positive animals, turnover in the herd, percentage of replacement with own stock and paratuberculosis prevalence in animals bought into the herd from outside, and a general hygiene-based factor. Diagnostic measures and time schedule used in the modelling approach are given by the paratuberculosis-control-programme of the local board for infectious disease control in food animals in the state of Lower Saxony. It was found by the model-calculations that in case of a high initial prevalence the anticipated six-year duration of the control programme is justified in order to ensure a lasting improvement of herd health. If hygienic measures are strictly obeyed and all test positive animals are culled a clear reduction on paratuberculosis prevalence can be achieved within the first year. According to the model in the second and third year the prevalence will increase again despite ongoing diagnostic measures in order to decrease again continuously with the beginning of the fourth year. Given an initial prevalence of 10%, 20% or 30% the prevalence after six years is calculated to be at 3%, 5% or 8% when all measures are followed as given in the control programme. The presented programme seems to be appropriate to predict prevalence development in paratuberculosis infected dairy herds if the herds are managed according to the guidelines of the "Tierseuchenkasse Niedersachsen", the local board for infectious disease control in food animals in the state of Lower Saxony, Germany. It becomes apparent that within six years a high decrease of the prevalence in the herds, but not a complete eradication of disease can be achieved by consistently complying with the rules given in these guidelines.     

A stochastic model simulating paratuberculosis in a dairy herd

Paratuberculosis (PTB) causes severe economic losses to farmers and the infection has very complex effects (many indirect) on the production of a dairy herd. These indirect effects have not or only briefly been described by earlier PTB-simulation models, and therefore they were included in a new model called PTB-Simherd. Our aim was to develop the basis for a decision-support tool which can predict herd-specific production-related effects from introduction of different control strategies against PTB. The PTB-Simherd is a dynamic, stochastic, and mechanistic Monte-Carlo model simulating a dairy herd including young stock. Paratuberculosis and relevant control strategies against this infection were built into an existing herd simulation model. The model simulates epidemiological and production related consequences of PTB and control strategies against it in the herd. It also reflects indirect effects of PTB and control strategies through effects on replacements and herd demographics. Every animal in the herd is specified with biological parameters (including PTB state and test results) and it is updated in weekly time-steps. Management is specified at herd level with 353 parameters of which 78 are related to PTB. To demonstrate the basic characteristics of the model, scenarios with varying infection risks (sensitivity analyses) plus scenarios with seven different control strategies in two herds with good and poor reproduction were simulated for 10 years. Breaking of infection routes turned out to be the only strategy predicted to reduce the true prevalence of PTB in a herd. Supplementing this strategy with test-&-cull strategies had limited effect on prevalence and using test-&-cull alone just delayed the increase in prevalence. The effects of different PTB-control strategies on the production (especially sale/purchase of heifers, feed consumption and prevalences of other diseases) were predicted to be affected by other conditions like heat-detection success, replacement% and herd demographics--which were again affected by PTB infection of the herd. These links and indirect effects of control strategies thus seem important to include when modeling and predicting effects of PTB control in dairy herds.     

Within-herd contact structure and transmission of Mycobacterium avium subspecies paratuberculosis in a persistently infected dairy cattle herd

Within-herd transmission of pathogens occurs either by direct or by indirect contact between susceptible and infected animals. In dairy herds that are structured into groups, the way in which animals encounter each other and share an environment can affect pathogen transmission. Dairy cattle are heterogeneous in terms of susceptibility and infectivity with respect to Mycobacterium avium subspecies paratuberculosis (Map) transmission. It is mainly young animals that are susceptible and adults that are infectious. Both vertical and horizontal transmission through the ingestion of Map shed into the environment by adults and transiently infected calves can occur. Our objective was to assess the effect of contact structure on Map transmission in persistently infected dairy herds and to examine the effect of isolating calves from other calves or from adults before weaning. We developed a stochastic compartmental model of Map transmission in a closed dairy herd. The model reflects the Map infection process and herd management characteristics. Indirect transmission via the environment was modelled explicitly. Six infection states (susceptible, resistant, transiently infectious, latently infected, subclinically infected, and clinically affected) and two contaminated farm area environments (whole farm and calf area) were modelled. Calves were housed in hutches, individual indoor pens, or group indoor pens. Two different levels of exposure of calves to a farm environment contaminated by adults were possible: no exposure and indirect exposure through fomites. Three herd sizes were studied. We found that contacts between calves before weaning did not influence Map transmission in a herd, whereas the level of exposure of calves to an environment contaminated by adults and the starting age of exposure of calves to adults were pivotal. Early culling of clinically affected adults led to a lower prevalence of infectious adults over time. The results were independent of herd size. Despite the many transmission routes that are known, the best control approach is to limit the exposure of calves to adult faeces through the systematic separation of adults and calves in combination with hygiene measures. Reducing contact between calves does not appear effective.     

Contagious impetigo in a dairy cattle herd

Abstract Impetigo and fürunculosis appeared in a dairy cattle herd in association with intensive showering of the lactating cows during the summer months. Heifers and dry cows in the same herd, as well as those in a neighbouring herd in the same village, which was not showered and served as a comparison herd, remained unaffected. Skin lésions declined with the termination of showering. Only six animals [three cows (7.3%) and three first-calving cows (20%)] had to be treated parenterally with antibiotics. Resumen En un rebafio de vacas de leche aparecieron cuadros de impetigo y fürunculosis asociados a las duchas frecuentes aplicadas durante los meses de verano a las vacas lactantes. Las novillas y vacas secas en el mismo rebaño, asi como las de un rebaño vecino de la misma localidad y que no recibian duchas fueron usadas como rebaño de comparación, no se vieron afectadas. Las lesiones cutáneas remitieron al dejar de aplicar las duchas. Tan solo en seis animales [tres vacas (7, 3%) y tres vacas en primer parto (20%)] fue necesario aplicar una terapia parenteral con antibióticos. [Yeruham, I., Elad, D., Perl, S., Nyska, A., Vishinsky, Y. Contagious impetigo in a dairy cattle herd (Impetigo contagioso en un rebaño de vacas de leche). Veterinary Dermatology 1996; 7 : 239–242.] Résumé Impétigo et füronculose se sont manifestés dans un troupeau laitier, en relation avec un douchage intensif des vaches allaitantes pendant les mois d'été. Les jeunes et les vaches taries du même troupeau, ainsi que celles d'un troupeau voisin du même village, non douchées et servant d'élément de comparaison, restèrent inaffectés. Les lésions cutanées ont régressé dês la cessation des douchages. Seuls six animaux (trois vaches-7, 3%-et trois vaches primipares-20%-) durent etre traités par antibiothérapie parentérale. [Yeruham, I., Elad, D., Perl, S., Nyska, A., Vishinsky, Y. Contagious impetigo in a dairy cattle herd (Impétigo contagieux dans un troupeau de vaches laitières). Veterinary Dermatology 1996; 7 : 239–242.] Zusammenfassung Eine Impetigo und Furunkulose trat bei einer Milchviehherde in Verbindung mit intensivem Abduschen bei den laktierenden Kühen während der Sommermonate auf. Färsen und trockenstehende Kühe in der selben Herde sowie die einer Nachbarherde im selben Ort, die nicht abgeduscht wurden und als Vergleichsgruppe dienten, blieben unverändert. Die Hautveränderungen reduzierten sich mit Beendigung des Abduschens. Nur sechs Tiere (drei Kühe (7, 3%) und drei Kalbinnen (20%)) mußten parenteral mit Antibiotika behandelt werden. [Yeruham, I., Elad, D., Perl, S., Nyska, A., Vishinsky, Y. Contagious impetigo in a dairy cattle herd (Ansteckende Impetigo bei einer Milchviehherde). Veterinary Dermatology 1996; 7 : 239–242.]     

Diagnosis of paratuberculosis in a dairy herd native to Brazil

Paratuberculosis (PTB) in Brazil has previously only been reported in imported animals and is officially considered as an exotic disease. A dairy herd, which had no imported animals, presented clinically suspect animals and was investigated for paratuberculosis using faecal culture, histopathology, indirect ELISA and the agar gel immunodiffusion test. Infection with Mycobacterium avium subsp. paratuberculosis (Map) was confirmed by culture of faeces from five cows with clinical symptoms of PTB and in 7/24 randomly selected asymptomatic cows from the same herd. Two cows with clinical symptoms were necropsied and their tissues were positive for Map by culture and histopathology. Twelve asymptomatic, randomly selected cows were positive on ELISA. The results confirmed the presence of PTB in this dairy herd and for the first time demonstrated the disease in a herd of native-bred cattle in Brazil.     

Eradication of paratuberculosis in dairy herds: determination of the initial herd prevalence and modelling of prevalence development

A prerequisite for the success of any eradication programme is the accurate determination of the initial herd prevalence as well as a herd-specific prediction of prevalence development. This prerequisite is not currently given for the eradication of paratuberculosis in infected herds. In the work presented a method to predict the initial paratuberculosis prevalence in infected herds is presented; it is based on the formation of two groups (ELISA-positive and negative) and the determination of generally applicable factors (positive predictive value [ppvn] of the ELISA and sensitivity of fecal culture in the ELISA-negative group [senF]). The ppvn of the ELISA was determined to be 0.6 based on the cultural examination of the ileocaecal lymph node of 64 ELISA-positive animals; the value for senF was set to be 0.64 based on the cultural examination of feces and ileocaecal lymph nodes of 40 ELISA-negative animals. To calculate the initial herd prevalence the number of animals in each of the groups was multiplied with the ppvn of the ELISA or with the reciprocal value of senF (1.5). The values were added and divided by the size of the herd. The practicability of this model was examined on nine herds with a total of 708 animals. The development of herd prevalence was modelled based on the examination scheme given in the paratuberculosis control programme of the "Nieders?chsische Tierseuchenkasse" (local board for infectious disease control in food animals in the state of Lower Saxony, Germany). For the calculation a yearly turnover-rate of 33% with restocking from within the herd and a possibility of paratuberculosis diagnosis only in animals two years and older were assumed. The development of herd prevalence is exemplarily presented for four herds with different initial prevalences.     

Neosporosis-like abortions in a herd of dairy cattle

Twenty-nine cows from a 240-cow drylot Holstein dairy in north-central New Mexico aborted over a period of approximately 5 months. Nine aborted fetuses were necropsied, and all but 1 of the fetuses were between 5 and 7 months of gestation. Microscopic examination of fetal tissues revealed focal necrotizing encephalitis and nonsuppurative myocarditis in 7 of the 9 fetuses. Additional lesions observed in some fetuses were focal hepatic necrosis, nonsuppurative myositis, focal necrotizing placentitis, focal nonsuppurative pneumonia, and focal nonsuppurative nephritis. A few groups of Neospora caninum-like protozoan organisms were observed adjacent to necrotic foci in the brain of 2 fetuses and in the kidney of a third fetus. No other cause of abortion was detected.     

Economic losses caused by paratuberculosis in a dairy herd: case report

The impact of clinical paratuberculosis in a 500 cow Jersey x Holstein dairy herd of loose housing system was followed up for three years. There was an increasing fall in annual milk production, namely 49, 474, and 1030 litres per cow, a decrease in the average age from 63.9 to 57.0 months, and of feed conversion from 60 to 39%. The effect of certain management deficiencies, existing throughout the study, is discussed.     

Factors affecting the herd level of antibodies against Mycobacterium avium subspecies paratuberculosis in dairy cattle

A case-control study was made of Norwegian dairy herds with high and low herd levels of antibodies against Mycobacterium avium subspecies paratuberculosis. A high proportion of the herds had a considerable number of seropositive cows, and environmental and management factors were examined for possible associations with the high serological levels of antibodies. The most important appeared to be: geographical location, red deer (Cervus elaphus) gaining access to the pastures for cattle, the observation of wild birds in the feed storage, and herds sharing common pasture with other herds of cattle. However, diagnostic tests showed that none of the animals in the case herds was infected with M a paratuberculosis.     

Salmonella Typhimurium persistence in a Hunter Valley dairy herd

OBJECTIVE: An epidemiological study was undertaken at a Hunter Valley dairy with persistent Salmonella Typhimurium infection. The aim of the study was to identify cattle currently or previously infected with Salmonella, possible sources of the organism, patterns of spread, and husbandry practices that could be improved. METHODOLOGY: Faecal samples, feed, water and environmental samples were cultured for Salmonella and blood samples were tested for antibodies against Salmonella (Dublin and Typhimurium). A questionnaire was designed to identify possible risk factors associated with Salmonella excretion. RESULTS: S Typhimurium was apparently introduced from an old to a new dairy through manure spread as fertiliser. Salmonella apparently persisted in the effluent pond, and the following year clinical cases occurred after pasture, irrigated with water from the pond, was grazed by dry cows, and adult cattle became clinically ill with salmonellosis. The disease spread to other cows and calves. Poor design of calf pens assisted spread of Salmonella from sick to healthy calves. In addition, there was suspected transmission to the dairy farmer's 9-month-old daughter. Salmonellosis on a farm is a potential zoonotic risk to farm workers and their families. There is also the risk that cull cows may carry Salmonella to the abattoir and subsequently into the human food chain. Methods of waste management, and the design of calf pens, were identified as major risk factors that could be improved to minimise the spread of salmonellosis on this property.     

Identification and control of paratuberculosis in a large goat herd

Mycobacterium paratuberculosis infection was detected in 2 goats in 1974 and in 5 goats in 1975; 5 of which were from a single herd. The magnitude of the subsequent epizootic in the goat herd was not recognized until 1977, when results of bacteriologic culture of fecal and tissue specimens, antibody determinations (agar-gel immuno-diffusion test), and histopathologic studies became available. By 1984, paratuberculosis had been diagnosed in 124 goats. Nearly all the goats were being used in antiserum production and had been given Freund complete adjuvant and human antigens. From 1974 to 1986, herd size varied from 100 to 300. The yearly incidence of paratuberculosis decreased from 13.2% (27 of 204 goats) in 1977 to 0% in 108 goats in 1985. The prevalence was higher in does. In goats that arrived on the farm in 1975 and before, 49 of 121 (40.5%) does developed paratuberculosis vs 41 of 120 (34.2%) wethers. In goats arriving on the farm in 1976 and after, 25 of 274 (8.5%) does and 9 of 216 (4.1%) wethers developed paratuberculosis. The average incubation period was approximately 4 years from arrival on the farm in every year except 1978, regardless of whether the goat was born on the farm or was purchased elsewhere.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transmission parameters of Mycobacterium avium subspecies paratuberculosis infections in a dairy herd going through a control program

A Johne's disease control program, including stringent management practices and a test-and-cull program (whole-herd fecal-samples taken twice a year), was implemented on a medium-sized Pennsylvania dairy farm that was suffering losses from clinical Johne's disease. The data that emerged from the control program, combined with birthdates, culling dates, lactation information and pedigrees, yielded an extensive longitudinal dataset. The dataset was processed through SAS 9.1 for statistical analysis; herd-level disease dynamics and dam-to-daughter transmission parameters were calculated. After the implementation of the program in 1984, prevalence dropped dramatically from 60% to less than 20% in 1989. After an apparent prevalence peak (25%) in 1991 due to improved test sensitivity, prevalence maintained a plateau of 10% from 1996 to 2000. After the implementation of the program, 9.5% of the offspring from test-negative dams and 26.8% of the offspring from known-infected dams became infected with Mycobacterium avium subspecies paratuberculosis (Map) (χ² = 14.7; p = 0.0001). Calves born shortly following the calving of an infected dam and calves growing up with a future high shedder were more likely to be infected compared to calves without this risk profile. It was concluded that, after the implementation of the control program, the most important causes of infections of susceptible calves were their own dams or infected animals which had calved recently.     

A herd level analysis of a Corynebacterium pseudotuberculosis outbreak in a dairy cattle herd

Corynebacterium pseudotuberculosis infection in an Israeli dairy cattle herd is described. The disease was characterized by ulcerative granulomatous lesions, which occurred in an epidemic form. Thirty-two cows and two heifers were affected, the ratio of the number affected to number at risk being 17.5 : 1 and 9.5 : 1, respectively. The culling rate was 50% of the affected animals. Most of the affected animals were cows (91.2%), with one first-calving cow (2.9%) and two heifers (5.9%) also affected. The infection occurred during the summer to autumn months (August-December), and lasted 118 days. The incubation period is about 2 months. The disease appeared in two clinical forms - cutaneous and mastitic - or as a mixed form. C. pseudotuberculosis organisms that were isolated from the ulcerative granulomatous lesions and from milk samples failed to reduce nitrate. A decrease in milk production (4%) and an increase in the bulk-milk somatic cell count from a herd mean of 240 x 10(3) mL(-1) to 460 x 10(3) mL(-1) were noted during the morbidity period. The organism was isolated from milk samples of eight animals (25%). Clinical, epizootiological and microbiological aspects of the infection are described.     

Eradication of Prototheca zopfii infection in a dairy cattle herd

Protothecosis is a severe form of mastitis in dairy cows caused by colorless algae of the genus Prototheca. Since P. zopfii is highly resistant to all known chemotherapeutics, infected cows must be removed from the herd. Eradication measures are difficult since many chronically infected cows may become intermittent shedders. Therefore, cultural methods are insufficient for control measures. In order to eradicate Prototheca zopfii-mastitis in dairy cattle herds, two isotype specific indirect ELISA for detection of IgA and IgG1 in whey were used in a dairy herd highly affected with protothecal mastitis. All cows (n = 313) were tested four times in intervals of six months. Milk specimens were examined in parallel by cultivation and serologically using two indirect ELISA systems for specific IgA and IgG1 in whey. Cows tested Prototheca positive were consequently separated from the herd and slaughtered. At the first examination, 15.6% of the animals were found positive by culture, and 23.3% were positive in at least one of the ELISA systems. Within two years, protothecal prevalence and incidence decreased to zero indicating that the eradication strategy used was successful. In summary, serological identification of P. zopfii-infected lactating cows is an useful tool to eradicate protothecal bovine mastitis in infected herds.     

Evaluation of serum and milk ELISAs for paratuberculosis in Danish dairy cattle

A milk and a serum ELISA for detection of antibodies against Mycobacterium avium ssp. paratuberculosis (MAP) were evaluated against the complement-fixation test (CFT) and culture of faecal samples from 580 cows collected between August 1996 and December 1996. Milk and serum were obtained concurrently from six dairy herds infected with MAP and from two dairy herds without history of infection with MAP.

A cut-off value of 7 OD% was used in the ELISAs. At this cut-off value, all six culture-positive herds were positive in the serum ELISA but one was negative in the milk ELISA. All six culture-positive herds were positive in the CFT. In the two culture-negative herds, the serum and the milk ELISA deemed all serum samples negative at this cut-off value, whereas four serum samples from one of these herds were positive in the CFT. The highest cut-off value enabling the milk ELISA to record all six culture-positive herds as positive was 4 OD%. The highest cut-off value enabling the serum ELISA to record all six culture-positive herds as positive was 17 OD%. Individual-sample relative sensitivities of the ELISAs ranged from 49 to 64% and relative specificities were 80–96% at the cut-off values of 4, 7 and 17 OD%.