Zoonotic risks of pathogens from dairy cattle and their milk-borne transmission.

Dairy products are major sources of high-quality protein and bioavailable nutrients and dairy production contributes to local, regional and national-level economies. Consumption of raw milk and raw milk products does, however, carry a zoonotic risk, as does direct contact with cattle by farm husbandry staff and other employees. This review will mainly focus on the latter, and deal with it from the standpoint of a well-developed dairy industry, using the example of the Netherlands. With regard to dairy cattle, the main bacterial pathogens are Salmonella spp., Listeria monocytogenes and Leptospira hardjo as well as Brucella abortus and Chlamydia abortus. The main viral pathogens associated with dairy are Rift Valley fever virus, rabies virus, cowpox virus and vaccinia virus. The main parasitological infections are Echinococcus granulosis, Cryptosporidium parvum and Giardia duodenalis, however, the last mentioned have mainly swimming pools as sources of human infection. Finally ectoparasites such as lice and mites and Trichophyton verrucosum may affect employees. Some pathogens may cause health problems due to contamination. Bacterial pathogens of importance that may contaminate milk are Campylolobacter jejuni, Escherichia coli, Mycobacterium avium subsp. paratuberculosis, Leptospira hardjo and Salmonella typhimurium. Excretion of zoonotic viruses in milk is negligible in the Netherlands, and the endoparasite, Toxocara vitulorum is mainly found in suckling and fattening calves, whilst the risk in dairy cattle is limited. Excretion of transmissible spongiform encephalopathies (TSEs) or mycoses in milk are not expected and are, therefore, not of importance here.Being aware of the risks and working according to hygiene standards can substantially limit zoonotic risks for employees. Additionally, diseased employees are advised to limit their contact with cattle and to indicate that they work with cattle when consulting a physician. To prevent zoonotic risks through excretion of pathogens in milk, standard hygiene measures are necessary. Further, using only pasteurised milk for consumption and/or processing of milk can considerably limit the risks. If these measures are not possible, well-constructed monitoring can be followed. Monitoring programmes already exist for pathogens such as for Salmonella spp., Leptospira hardjo and Mycobacterium avium subsp. paratuberculosis. For others, like Campylobacter jejuni and E. coli, programmes are not available yet as far as we know.

Evaluation of test characteristics of 2 ELISA tests applied to bulk tank milk and claw-trimming records for herd-level diagnosis of bovine digital dermatitis using latent class analysis.

Bovine digital dermatitis (DD) is an infectious claw disease with a negative effect on animal welfare and production. Treponema spp. is the main causative agent, and infected animals produce specific antibodies. Our aim was to estimate sensitivity (Se) and specificity (Sp) of 2 ELISA research tests, Medicago's ELISA test and GD Animal Health's in-house ELISA test, for detection of DD-associated Treponema antibodies in bulk tank milk. We used bulk tank milk samples from 154 Norwegian dairy cattle herds, 96 from an expected high-prevalence region and 58 from a low-prevalence region. Both tests were evaluated separately against herd-level (aggregated) claw-trimming records extracted from the Norwegian Dairy Herd Recording System using latent class models in a Bayesian analysis. Cutoff values were selected using an explorative approach, and both noninformative priors for all parameters and informative ß priors for distribution of Se and Sp of claw trimming were explored. The estimated (median) true herd-level prevalence of digital dermatitis varied between 24 and 30% in the high-prevalence region and between 3 and 6% in the low-prevalence region. For Medicago's ELISA test, an Se (95% posterior credible interval) of 0.57 (0.32; 0.94) could be achieved without compromising Sp, and for GD Animal Health's in-house ELISA test, an Se of 0.60 (0.37; 0.92) was achieved. Our study showed that both ELISA tests can detect antibodies against DD-associated Treponema spp. in bulk tank milk. However, neither of the 2 ELISA tests produced satisfactory sensitivity without compromising specificity. Based on these results, inspection at claw trimming in a chute is necessary for surveillance and control of DD at the herd level in Norway, although these ELISA tests of bulk tank milk might be a useful supplement.

A proposed structural approach to improve cow-claw health on Dutch dairy farms.

Despite extensive research leading to an improved understanding of the risk factors and pathogenesis of infectious and non-infectious disorders, claw health has not structurally improved in recent decades. Several studies have shown that claw disorders harm milk production, fertility and longevity of the dairy cows and job satisfaction of the farmer. This is enough reason to structurally improve claw health on dairy farms. The focus should be on a rapid curative intervention when lameness occurs and above all the prevention of claw problems. Most claw disorder diagnoses are nowadays made during regular claw trimming by the professional trimmer or the dairy farmer. Registration of the detected disorders during claw trimming is not always done consistently, so the estimated prevalence (number of cows with a claw disorder) is in most cases an underestimation of the real prevalence. The quality of these records often makes it difficult for consultants to formulate appropriate claw health advice. To be able to give good advice on claw health, insight into the prevalence of the various hoof disorders on a farm is a key condition. However, good quality advice alone is not a guarantee for an improved claw health situation on a farm. Research has shown that in addition to high quality substantiated advice, the communication style between the consultant and the dairy farmer is essential for the interpretation and motivation of the dairy farmer to implement the advice. In this paper a 7-point plan is presented as a guidance for herd advisors who want to support dairy farmers to improve claw health.

An Evaluation of a Parenteral Antibiotic Treatment of Cattle with Non-Healing Claw Horn Lesions.

Non-healing claw horn disorders are a serious problem in dairy herds because of the long duration of the disorder and the chronic pain derived from it, seriously affecting animal welfare and causing decreased production and premature culling from the herd. In a clinical trial, 40 cows in 13 herds (12 dairy herds and 1 herd with cow-calf operations) with toe necrosis (TN, 27x) or a non-healing white line disorder (NHWLD, 13x) were treated topically with an unguent-containing zinc sulphate and acetyl acid in combination with a parenteral injection of tilmycosin. An evaluation was conducted 3 months after treatment using locomotion scoring (LS), a clinical observation of the lesion, and the lactation value (the lactation value is the Net Profit of the individual animal divided by the average Net Profit of the entire herd. The mean is 100, so >100 is related to better production (combination of kg milk, %fat, and protein)) (LV) before and after treatment. The mean LS improved significantly from 4.0 (SD: 0.2) before treatment to 1.2 (SD: 0.4) 3 months after treatment (p < 0.001). The clinical presentation showed that all of the cows were cured from horn shoe infection (both TN and NHWLD). The LVs of the treated cows increased significantly from 111.2 (SD: 12.2) to 116.8 (SD: 15.1; p = 0.003).

An In-House ELISA for Treponema Antibodies in Bulk Milk as Part of a Monitoring Tool for Claw Health in Dairy Herds.

Digital dermatitis (DD) is a painful inflammation at the coronary band of the claws, a major cause of lameness in cattle and associated with infections with several Treponema spp. Clinical inspection of the feet is the best way to diagnose DD, but this is laborious and stressful for cattle. A simple diagnostic tool was developed to monitor DD prevalence at the herd level. An antibody ELISA based on antigens from four different Treponema spp. has been developed and validated in two field studies. In one study, bulk milk and individual milk samples of seven dairy herds, of which clinical claw scores were obtained, were tested. In the second study, bulk milk was tested from 110 herds of which clinical scores were obtained. A weak correlation between clinical scores of cows and the ELISA results in individual milk samples was observed. The ELISA response in bulk milk was higher in herds with higher mean clinical scores. Using the ELISA results in bulk milk, herds with a low or high proportion of cattle with DD lesions could be distinguished. This ELISA is useful to obtain insight into the DD status at the herd level, and is nowadays being used in a claw health monitoring program for dairy cattle in the Netherlands.

Simulating the mechanics behind sub-optimal mobility and the associated economic losses in dairy production.

Hoof disorders and sub-optimal mobility (SOM) are economically important health issues in dairy farming. Although the dynamics of hoof disorders have an important effect on cow mobility, they have not been considered in previous simulation models that estimate the economic loss of SOM. Furthermore, these models do not consider the varying severities of SOM. The objective of this study was to develop a novel bio-economic simulation model to simulate the dynamics of 8 hoof disorders: digital dermatitis (DD), interdigital hyperplasia (HYP), interdigital dermatitis/heel-horn erosion (IDHE), interdigital phlegmon (IP), overgrown hoof (OH), sole haemorrhage (SH), sole ulcer (SU) and white-line disease (WLD), their role in SOM, and estimate the economic loss of SOM in a herd of 125 dairy cows. A Reed-Frost model was used for DD and a Greenwood model for the other 7 hoof disorders. Economic analysis was conducted per mobility score according to a 5-point mobility scoring method (1 = perfect mobility; 5 = severely impaired mobility) by comparing a scenario with SOM and one without SOM. Parameters used in the model were based on literature and expert opinion and deemed credible during model validation rounds. Results showed that the mean cumulative incidence for maximum mobility scores 2-5 SOM episodes were respectively 34, 16, 7 and <1 episodes per 100 cows per pasture period and 39, 19, 8, <1 episodes per 100 cows per housing period. The mean total annual economic loss due to SOM resulting from the hoof disorders under study was €15,342: €122 per cow per year. The economic analysis uncovered direct economic losses that could be directly linked to SOM episodes and indirect economic losses that could not be directly linked to SOM episodes but arose due to the presence of SOM. The mean total annual direct economic loss for maximum mobility score 2-5 SOM episodes was €1129, €3098, €4354 and €480, respectively. The mean total annual indirect economic loss varied considerably between the 5th and 95th percentiles: €-6174 and €19,499, and had a mean of €6281. This loss was composed of additional indirect culling due to SOM (∼65%) and changes in the overall herd milk production (∼35%) because of additional younger replacement heifers entering the herd due to increased culling rates. The bio-economic model presented novel results with respect to indirect economic losses arising due to SOM. The results can be used to stimulate farmer awareness and promote better SOM management.

Longitudinal study of the immune response and memory following natural bovine respiratory syncytial virus infections in cattle of different age.

Human and bovine respiratory syncytial virus (HRSV and BRSV) are closely genetically related and cause respiratory disease in their respective host. Whereas HRSV vaccines are still under development, a multitude of BRSV vaccines are used to reduce clinical signs. To enable the design of vaccination protocols to entirely stop virus circulation, we aimed to investigate the duration, character and efficacy of the immune responses induced by natural infections. The systemic humoral immunity was monitored every two months during two years in 33 dairy cattle in different age cohorts following a natural BRSV outbreak, and again in selected individuals before and after a second outbreak, four years later. Local humoral and systemic cellular responses were also monitored, although less extensively. Based on clinical observations and economic losses linked to decreased milk production, the outbreaks were classified as moderate. Following the first outbreak, most but not all animals developed neutralising antibody responses, BRSV-specific IgG1, IgG2 and HRSV F- and HRSV N-reactive responses that lasted at least two years, and in some cases at least four years. In contrast, no systemic T cell responses were detected and only weak IgA responses were detected in some animals. Seronegative sentinels remained negative, inferring that no new infections occurred between the outbreaks. During the second outbreak, reinfections with clinical signs and virus shedding occurred, but the signs were milder, and the virus shedding was significantly lower than in naïve animals. Whereas the primary infection induced similar antibody titres against the prefusion and the post fusion form of the BRSV F protein, memory responses were significantly stronger against prefusion F. In conclusion, even if natural infections induce a long-lasting immunity, it would probably be necessary to boost memory responses between outbreaks, to stop the circulation of the virus and limit the potential role of previously infected adult cattle in the chain of BRSV transmission.

Levels of trace elements and potential toxic elements in bovine livers: A trend analysis from 2007 to 2018.

Trace elements and potential toxic elements were analyzed in bovine livers submitted for autopsy in the Netherlands during the years 2007 to 2018. The age of each animal was recorded. In total, 1544 livers were analyzed for cadmium, cobalt, chromium, copper, iron, molybdenum, nickel, lead, selenium and zinc. Less than 2% of the liver samples were from veal calves. Young animals had significantly higher concentrations of iron and zinc in their livers compared to animals older than one year, while older animals had significantly higher levels of cadmium and molybdenum in their livers. Animals aged 1 to 2 years had the lowest copper and selenium levels. There was a tendency for lower chromium and nickel levels during the last years of the testing period, while copper showed an increase. Lead intoxication was only seen in the youngest group of cattle, while copper intoxication, defined as a liver copper of more than 1000 mg/kg dry matter, occurred in older animals, mainly in animals of 3 to 4 years old. This trend analysis of trace elements in bovine livers of cattle over time in recent years, and the relation of liver element concentrations with age of the animal, provides insight in the uptake and storage of these elements by cattle in The Netherlands. Possible reasons for observed trends and age-related patterns are discussed.

Clinical course of digital dermatitis lesions in an endemically infected herd without preventive herd strategies.

Lactating Holstein-Friesian dairy cows in four separately housed groups in a herd with endemic digital dermatitis (DD) were monitored weekly for 4 weeks in December 2004 for the presence of and transition between five stages (M0-M4) of DD. Cows were also monitored for the presence of heel horn erosion (HHE) and interdigital hyperplasia. Prior to the study, two groups had been housed indoors on a high or low energy ration, one group had been grazed and one was a dry cow group. All cows received the same ration during the period of investigation. 'Active infection' was defined as transition from M0, M1, M3 or M4 to M2 and 'resolving M2 lesions' were defined as transition from M2 to another stage. M2 lesions were diagnosed on 106 occasions in the hind claws of 49 (36%) of 138 dairy cows; both hind claws were affected in nine cases (18%). M2 lesions were more often painful on palpation than other stages; 94% of M2 lesions were located plantar-medially near the interdigital cleft and 71% had a diameter of 2-4 cm. More M1 lesions than other stages were found within the interdigital space. When interdigital hyperplasia was present, claws were always concurrently affected by DD. The baseline incidence for 'active infection' was 6% per week, increasing to 11% when HHE was present, 14% when cows were previously housed indoors and fed a high energy ration and 16% when cows were 60-120 days in lactation. Topical treatment with chlortetracycline resulted in resolution from M2 of 79% per week. There were no significant effects of group, stage of lactation, parity or HHE on resolution of M2 lesions.

[Reintroduction of E. granulosus by import of cows in the Netherlands]. / Herintroductie van echinococcose via runderimport in Nederland.

Since East European countries joined the EU, the import of both dairy and beef cows from these countries increased considerably. Based on the identification and registration system it turned out that in the period from May until December 2007 about 200 cows per month were imported from Romania. These animals were either slaughtered immediately or in autumn. In autumn, cysts were noticed both in slaughtered cows during meat inspection and in deceased animals (originated from Romania) during postmortem investigation performed by the Animal Health Service. Because cysts were strongly reminiscent of Echinococcus granulosus hydatid cysts, samples were sent to the authorized laboratory (National Reference Laboratory of Parasitology), where the reintroduction of this potentially zoonotic parasitic infection has been confirmed. The risks of reintroduction of E. granulosus in the Netherlands are described.

[Infectious bovine rhinotracheitis outbreak on a mostly BHV-1 free farm can result in great damage]. / Infectieuze boviene rhinotracheïtisuitbraak op een nagenoeg BHV1-vrij bedrijfkan tot grote problemen leiden.

In a suckler herd with 110 cows (without young stock born in 2003) 5 cows died within 10 days, 6 calves were born dead prematurely and 5 calves were born alive but prematurely. The diagnosis BHV1-infection was based on clinical symptoms and confirmed with PCR. The clinical signs, diagnostic methods, therapy, risk-analysis and prevention are discussed.

The dynamics of digital dermatitis in populations of dairy cattle: model-based estimates of transition rates and implications for control.

Five groups of dairy cows affected by digital dermatitis were subjected to five different footbath strategies and evaluated at regular 3-weekly intervals. A standard protocol was used to record five different stages of disease from early (M1), acute ulcerative (M2), healing (M3) and chronic lesions (M4) in addition to the negative stage of disease (M0). The effect of the footbathing was evaluated using mathematical modelling for the transmission dynamics of infections and summarized using the reproduction ratio R(0). Sensitivity analysis for a range of parameters in the mathematical model showed that the speed of detecting acute lesions and the efficiency with which those lesions were treated were the key parameters which determined whether lesions became more severe or whether they healed.

The effect of an acidified, ionized copper sulphate solution on digital dermatitis in dairy cows.

Digital dermatitis (DD) is the most important infectious claw disorder in dairy cattle and herd-based foot bathing with antibacterials, such as 4% formalin, is often used to prevent it. However, there is a lack of long-term studies of the effectiveness of such regimes and in this study the preventive and curative effect of 4% formalin was compared with that of an acidified, ionized copper sulphate solution over a 4-month period on a commercial 120-cow dairy farm. The cows were walked through a split-leg footbath where left claws were treated with an acidified copper solution twice daily for 5 days/week, while right claws were treated with 4% formalin twice daily for 1 day/every second week. Hind claws were scored for the presence and severity of DD in a trimming chute at the start of the study and every 4 weeks throughout the study period. At the start of the study 21/110 cows had ulcerative DD lesions with 10 on the left hind foot, 8 on the right and 3 on both. These lesions, as well as any new lesions which arose during the study, were treated with chlortetracycline spray. During the study 440 observations were made and seven new DD lesions were recorded on left feet (copper treated) and 20 on right feet (formalin treated). Based on survival analysis, the risk of developing a new ulcerative DD lesion on copper-treated (left hind) feet was almost three times less (RR=0.37, 95% CI 0.16-0.91) than formalin-treated (right hind) feet. Cure rates of DD lesions were not different between copper and formalin.

Prevalence, prediction and risk factors of enteropathogens in normal and non-normal faeces of young Dutch dairy calves.

Between January and April 2007, 424 calves under 22 days of age from 108 Dutch dairy herds were sampled to estimate the prevalence of non-normal faeces ('custard-like'-yellowish-coloured with custard consistency or diarrhoea: watery-like faeces) and the shedding of enteropathogens Escherichia coli K99 (E. coli), Coronavirus, Cryptosporidium parvum (C. parvum), Rotavirus and Clostridium perfringens (Cl. perfringens). In addition, information was collected on animal characteristics and herd-management practices. The probability of detecting each one of five enteropathogens given a calf with 'custard-like' faeces or diarrhoea was estimated using Bayes' rule and was based on the predicted probabilities from a multinominal model including each of five enteropathogens as independent variables. In addition, putative risk factors for the presence of each of five enteropathogens were analysed using logistic regression models with random herd effects. Fifty-seven percent of calves had faeces of normal colour (brownish) and consistency (firm), 23.8% (95%CI: 19.8-28.2%) had 'custard-like' faeces and 19.1% (95%CI: 15.5-23.2%) had diarrhoea. E. coli was the least detected enteropathogen (2.6% (95%CI: 1.3-4.6%) of calves, 9% (95%CI: 5-16%) of herds) and Cl. perfringens was most detected (54.0% (95%CI: 49.1-58.8%) of calves, 85% (95%CI: 77-91%) of herds). E. coli and Coronavirus were detected incidentally in only one or two calves per herd, whereas C. parvum and Cl. perfringens were frequently detected in up to four calves per herd. For calves with 'custard-like' faeces, the probability of detecting Rotavirus from a calf in its first week of age was 0.31 whereas for a calf in its second week, there was a 0.66 probability of detecting C. parvum. The probabilities of detecting E. coli, Rotavirus and C. parvum in calves with diarrhoea in their first week of age were 0.10, 0.20 and 0.43, respectively. In calves with diarrhoea between 1 and 2 weeks of age, the probability of detecting enteropathogens was 0.43 for C. parvum. None of the tested enteropathogens were related to 'custard-like' faeces or diarrhoea in the third week of age. Putative risk factors for E. coli, Coronavirus and C. parvum included the presence of peer-calves shedding Coronavirus, C. parvum or Rotavirus, respectively. Additionally, managerial risk factors such as non-optimal hygienic housing (for Coronavirus) and the routine use of antibiotics for diarrhoeic calves (for C. parvum) were found. No animal or managerial factors were associated with shedding of Cl. perfringens.