Investigation, management and control of a maedi outbreak in Norway in 2019-2020.

BACKGROUND: Visna-maedi is a notifiable disease in Norway, and eliminating the disease is a national goal. The import of sheep into Norway is very limited, and strict regulations apply to the movement of small ruminants between flocks and within defined geographical regions. Several outbreaks have occurred in the last 50 years, and the most recent before 2019 occurred in Trøndelag county in Central Norway in 2002. A national surveillance programme for small ruminant lentivirus infection exists since 2003. RESULTS: In 2019, the national surveillance programme detected seropositive animals for small ruminant lentivirus in a sheep flock in Trøndelag. Based on the result of polymerase chain reaction analysis and histopathological findings, the Norwegian Food Safety Authority concluded the diagnosis of maedi. Further investigations detected maedi in eight additional sheep flocks in the same county. The flocks were placed under restrictions, and the authorities also imposed restrictions on 82 contact flocks. Sequencing of partial gag genes indicated that the virus in the current outbreak was related to the small ruminant lentivirus detected in the same area between 2002 and 2005. CONCLUSIONS: The outbreak investigation shows the need for sensitive and specific diagnostic methods, and an improved and more targeted surveillance strategy. It also demonstrates the risk of disease spreading between flocks through animal movements, and highlights the importance of biosecurity and structured livestock trade. In addition to allowing livestock trade only from flocks documented free from maedi, it may be necessary to monitor sheep flocks over many years, when aiming to eliminate maedi from the Norwegian sheep population.

Excretion of Eimeria spp. oocysts in young lambs following iron supplementation.

BACKGROUND: Iron is an essential nutrient, and iron supplementation has been shown to reduce the incidence of abomasal bloat in lambs. Additionally, iron deficiency is linked to pica, which may increase uptake of Eimeria oocysts. Coccidiosis in sheep, caused by Eimeria spp., is an important infection, leading to reduced welfare and economic losses. The aims of our study were to investigate: (1) the use of iron supplementation in Norwegian sheep flocks using a questionnaire survey, and (2) whether iron supplementation reduced excretion of Eimeria oocysts and increased the growth rates of young lambs. RESULTS: A questionnaire regarding the use of iron supplementation, sent to all members of the Norwegian Sheep Recording System (n = 4993), showed that 152/1823 farmers iron-supplemented lambs, either orally (56.7%) or by injection (43.3%). The main purpose of supplementation was to prevent abomasal bloat (38.4%), coccidiosis (9.3%), or both (27.8%). In the field study, 102 twin lambs from five flocks were included: one twin (treated) received 600 mg of gleptoferron subcutaneously within 3 days of birth, whereas the control was given saline. McMaster analysis of individual faecal samples obtained at weekly intervals (n = 4 per lamb, starting at turnout) showed no significant difference in oocyst excretion between treatment groups at any sampling, except for one flock 14 days after turnout. Mean growth rates, measured at iron injection, 21 days after turnout, and in the autumn, differed significantly between treated and untreated lambs from iron injection to 21 days after turnout, however, no difference in growth rates was observed in the overall period from iron injection to autumn. Blood analysis suggested that the controls were at risk of developing iron deficiency anaemia during the housed period, but signs of anaemia were not observed. CONCLUSION: Iron supplementation of lambs was used by 8.3% of the farmers responding to the questionnaire, mainly with the intention to prevent abomasal bloat, coccidiosis, or both. The field trial results indicate that iron supplementation of young lambs do not reduce oocyst excretion and only induced a transitory increase in weight gain. However further studies, including more flocks and possibly repeated iron injections, would provide more definitive information.

A financial cost-benefit analysis of eradicating virulent footrot.

In 2008, virulent footrot was detected in sheep in south-west Norway. Footrot is caused by Dichelobacter nodosus, and the outbreak was linked to live sheep imported from Denmark in 2005. A large-scale program for eradicating the disease was implemented as a joint industry and governmental driven eradication project in the years 2008-2014, and continued with surveillance and control measures by the Norwegian Food Safety Authority from 2015. The cost of the eradication program including surveillance and control measures until 2032 was assumed to reach approximately €10.8 million (NOK 90 million). A financial cost-benefit analysis, comparing costs in the eradication program with costs in two simulated scenarios, was carried out. In the scenarios, designated ModerateSpread (baseline) and SlowSpread, it was assumed that the sheep farmers would undertake some voluntary measures on their own that would slow the spread of the disease. The program obtained a positive NPV after approximately 12 years. In a stochastic analysis, the probabilities of a positive NPV were estimated to 1.000 and to 0.648 after 15 years and to 0.378 and 0.016 after ten years, for the ModerateSpread and SlowSpread scenarios respectively. A rapid start-up of the program soon after the detection of the disease was considered crucial for the economic success as the disease would have become more widespread and probably raised the costs considerably at a later start-up.

The potential spread of severe footrot in Norway if no elimination programme had been initiated: a simulation model.

When severe footrot was detected in Norway in 2008, a surveillance programme was initiated and followed by an elimination programme. By 2013 the disease had spread to two of 19 counties and a total of 119 (1%) sheep flocks had been diagnosed with severe footrot. A simulation model was developed to estimate the potential spread of severe footrot in Norway and to estimate the relative importance of the different spreading routes. The model parameters were based on the rate of spread of the first 38 diagnosed cases and the management and climatic factors particular for Norway. The model showed that by 2013, severe footrot would have spread to six counties and infected 16% of the sheep flocks if no elimination programme had been initiated. If this is compared with the 1% of flocks that were diagnosed in Norway by 2013, there seems to be a large effect of the implemented footrot elimination programme. By 2035, it was estimated that severe footrot would have spread to 16 counties and 64% of the sheep flocks. Such an extensive spread would probably impose a large negative impact on the sheep industry and welfare of the sheep. The most effective way to curb the spread of severe footrot was by decreasing the within county infection rate. This could be achieved by decreasing the contact between flocks or by decreasing the environmental load of D. nodosus, for example by footbathing sheep, culling diseased sheep or eliminating severe footrot in the flock.

A recently introduced Dichelobacter nodosus strain caused an outbreak of footrot in Norway.

BACKGROUND: In 2008, an outbreak of ovine footrot occurred in Norway. Dichelobacter nodosus isolates collected between 2008 and 2011 have been characterised. Isolates defined as virulent by the gelatin gel test (GG-test) were only found in sheep in Rogaland County, where the severe cases of footrot were registered. The majority (96%) of the virulent isolates belonged to serogroup A. It is suspected that they represent a newly introduced strain, and the aim of the present study was to investigate whether they are genetically similar. Sixty-one virulent isolates from sheep and 116 benign isolates from sheep, cattle and goats were included. Four GG-test virulent isolates from Danish sheep were also included. All isolates were genotyped by pulsed-field gel electrophoresis (PFGE) and by PCR for pgr variant determination. RESULTS: The Norwegian virulent isolates were assigned to 8 pulsotypes (PTs), while the benign isolates were assigned to 66 PTs. Thirty-seven (68.5%) of the 54, virulent, serogroup A isolates belonged to the same PT, and included isolates from 2008 through 2011. Isolates belonging to this PT were defined as the outbreak strain. The remaining virulent serogroup A isolates belonged to 4 PTs differing by ≤3 bands from the outbreak strain. Two virulent, Danish, serogroup A isolates differed by 2 bands from the Norwegian outbreak strain. All but 3 (95%) of the virulent isolates had the pgrA variant while 85% of the benign isolates had the pgrB variant. CONCLUSION: This study provides evidence that the footrot outbreak in Norway in 2008 most likely was caused by new introduction and local spread of one virulent D. nodosus strain.

Cross-infection of virulent Dichelobacter nodosus between sheep and co-grazing cattle.

Dichelobacter nodosus is the main aetiological agent of ovine footrot and the bacterium has also been associated with interdigital dermatitis is cattle. The aim of this study was to investigate possible cross-infection of virulent D. nodosus between sheep and co-grazing cattle. Five farms, where sheep previously diagnosed with virulent D. nodosus were co-grazing with cattle for different periods of time, were included. The study sample consisted of 200 cows and 50 sheep. All cows were examined for the presence of interdigital dermatitis, and ten ewes, preferably with symptoms of footrot, had the footrot scores recorded. On each farm, the same ten ewes and ten cows were chosen for bacterial analyses. Swabs were analysed for D. nodosus by PCR and culturing. D. nodosus isolates were virulence-tested and assigned to serogroups by fimA variant determination. Biopsies were evaluated histopathologically and analysed by fluorescent in situ hybridization for D. nodosus, Treponema spp. and Fusobacterium necrophorum. D. nodosus defined as virulent by the gelatin gel test were isolated from 16 sheep from four farms and from five cows from two of the same farms. All five cows had interdigital dermatitis. Two of the cows stayed infected for at least eight months. By pulsed-field gel electrophoresis (PFGE), the isolates from the five cows were found to be genetically indistinguishable or closely related to isolates from sheep from the same farm. This indicates that cross-infection between sheep and cows have occurred.

A longitudinal study of the risks for introduction of severe footrot into sheep flocks in the south west of Norway.

In 2008, ovine footrot was detected in Norway for the first time since 1948. By December 2012 it had spread to 99 flocks, all in the county of Rogaland in the south west of Norway, and 42% of which were located in the municipality of Rennesøy in Rogaland. The aim of this study was to investigate risk factors for contracting severe footrot in flocks of sheep. A flock was considered positive for severe footrot based on positive virulence test or by clinical signs in addition to a positive PCR test. A retrospective longitudinal study was performed with a questionnaire as the main data source. All sheep farmers (107) in the municipality of Rennesøy were selected for inclusion in the study. The questions focused on direct and indirect contacts between sheep in different sheep flocks and general information about the farm. The questions covered the years 2007-2011. Data were analysed using discrete time survival modelling. A total of 81 (76%) farmers responded to the questionnaire including 29 of 41 (71%) farmers with flocks positive for severe footrot. Factors that increased the risk of a flock becoming positive for severe footrot in the final multivariable survival model were sheep that trespassed boundary fences and came into contact with a flock positive for severe footrot (odds ratio 11.5, 95% confidence interval 4.1-32.2) and at least one flock with severe footrot within 0-1km radius of a farm (odds ratio 8.6, 95% confidence interval 2.3-32.6). This study highlights the importance of upgrading and maintaining boundary fences and encouraging farmers to avoid direct and indirect contact between nearby flocks.

Prevalence of gastrointestinal helminths, lungworms and liver fluke in sheep and goats in Norway.

The present study describes the occurrence of various gastrointestinal helminths, lungworms and liver flukes in Norwegian sheep and goats as assessed from faecal samples and post mortem examinations performed between 2007 and 2010. Faecal samples for gastrointestinal nematode egg counts were collected from 77 sheep flocks and 30 dairy goat flocks from three geographical regions in Norway. Additionally, thirty-two lambs and 16 adult goats were euthanized for necropsy examination and for identification of adult gastrointestinal nematodes and tapeworms, lungworms and liver flukes. The survey showed that there was a higher mean excretion of trichostrongyle eggs in sheep than in goats at the individual level (392 EPG vs. 154 EPG, p<0.001). For both host species, the mean prevalence and intensity of excreted trichostrongyle eggs were significantly higher in the southern coastal region compared with the inland and northern regions (p<0.001). Third stage larvae of Trichostrongylus/Teladorsagia, Haemonchus and Nematodirus type were the most prevalent ones in the coprocultures from sheep, whereas larvae of Trichostrongylus/Teladorsagia and Nematodirus type dominated in goats. The most prevalent gastrointestinal nematode species found at necropsy was Teladorsagia circumcincta (75.0 and 81.2% respectively in sheep and goats), while the largest mean worm burdens were recorded for Haemonchus contortus in sheep (724±623) and T. circumcincta in goats (377±529). Other gastrointestinal nematode species were present at low prevalence or in low numbers. Fasciola hepatica was only found in necropsied sheep from the coastal region with a prevalence of 18.8%. The lungworm Mullerius capillaris was found from all regions in necropsied goats (31.2%) and from coastal area in sheep (3.1%). The present study indicates that H. contortus and Nematodirus battus have a wider geographical distribution to the north than expected, and describes to our knowledge the northernmost occurrence of H. contortus in the Nordic countries.

Characterisation of Dichelobacter nodosus isolates from Norway.

An outbreak of ovine footrot in Norway in 2008, the first reported since 1948, prompted action to investigate Norwegian isolates of Dichelobacter nodosus. A total of 579 isolates from 124 different farms were characterised. These included 519 isolates from sheep, 52 isolates from cattle and 8 isolates from goats. The potential virulence of the isolates was assessed by the gelatin gel test (GG-test) and the elastin agar test, that test the heat stability and elastase activity of bacterial proteases, respectively. The isolates were also tested for the presence of intA by PCR, and allocated to serogroups by differentiation of fimA variants using multiplex PCR or sequencing. Thirty of the isolates were also serogrouped by slide agglutination. Three hundred and five isolates were defined as virulent by the GG-test. All these were from sheep from 52 farms located in the county of Rogaland in the south west of Norway. All isolates from cattle and goats were defined as benign by the GG-test. IntA was only detected in 6 (2.0%) of the virulent isolates. All serogroups except D and F were detected. Three hundred and seventy-two (64.3%) of the isolates belonged to serogroup A, and 96% of the virulent isolates belonged to this serogroup. On the grounds that virulent isolates were only found in one county, and that the majority belonged to the same serogroup (A), it is believed that a virulent D. nodosus strain was introduced to Norway relatively recently and that so far it has only spread locally.

Prevalence of anthelmintic resistance in gastrointestinal nematodes of sheep and goats in Norway.

In the period of 2008­2009, the efficacies of the benzimidazole (BZ) albendazole and the macrocyclic lactone (ML) ivermectin against gastrointestinal nematodes (GIN) of small ruminants were evaluated by means of the fecal egg count reduction (FECR) test and by post-treatment identification of surviving third stage (L3) larvae after coproculture. Sheep (n=28) and goat (n=28) flocks from three areas of Norway were randomly selected to assess the prevalence of anthelmintic resistance (AR), whereas only lambs from non-randomly selected sheep flocks (n=32) with a farm management that could select for AR were investigated the second year. Only flocks with a mean excretion of nematode eggs per gram feces (EPG) ≥ 150 at time of treatment were included in the survey. In total, 48 (80%) and 13 (46.4%) of the selected sheep and goat flocks, respectively, fulfilled the inclusion criteria. The proportions of flocks classified as resistant (i.e., FECR <95% and with a lower 95% confidence interval of <90%) for the BZ drug albendazole were 10.5% and 31.0% in the randomly and non-randomly selected sheep flocks, respectively. When restricting the area to Rogaland County, eight flocks out of ten (80%) non-randomly selected sheep flocks showed BZ resistance. The efficacy of ML was 100% in all surveyed sheep and goat flocks. In post-treatment coprocultures from the non-randomly selected flocks, the main nematode genera were Teladorsagia/Trichostrongylus in five flocks, Haemonchus in two flocks, and a mixture of these genera in the remaining two flocks. In the goat flocks, the pre-treatment infection levels of GIN were low compared to what was found in the sheep flocks. Still, in one flock, AR against BZ in Teladorsagia/Trichostrongylus was found. New strategies and recommendations to face the emerging AR situation in Rogaland County in order to limit the spread of resistant nematodes within and into other areas are urgently needed.

Worm control practice against gastro-intestinal parasites in Norwegian sheep and goat flocks.

BACKGROUND: Anthelmintic treatment is the most common way of controlling nematode infections in ruminants. However, several countries have reported anthelmintic resistance (AR), representing a limitation for sustainable small ruminant production. The knowledge regarding worm control management represents a baseline to develop a guideline for preventing AR. The aim of the present study was therefore to improve our knowledge about the worm control practices in small ruminant flocks in Norway. METHODS: A questionnaire survey regarding worm control practices was performed in small ruminant flocks in Norway. Flocks were selected from the three main areas of small ruminant farming, i.e. the coastal, inland and northern areas. A total of 825 questionnaires, comprising 587 sheep flocks (return rate of 51.3%) and 238 goat flocks (52.6%) were included. RESULTS: The results indicated that visual appraisal of individual weight was the most common means of estimating the anthelmintic dose used in sheep (78.6%) and goat (85.1%) flocks. The mean yearly drenching rate in lambs and ewes were 2.5 ± 1.7 and 1.9 ± 1.1, respectively, whereas it was 1.0 (once a year) in goats. However, these figures were higher in sheep in the coastal area with a rate of 3.4 and 2.2 in lambs and ewes, respectively. Benzimidazoles were the predominant anthelmintic class used in sheep flocks (64.9% in 2007), whereas benzimidazoles and macrocyclic lactones were both equally used in dairy goat flocks. In the period of 2005-2007, 46.3% of the sheep flocks never changed the anthelmintic class. The dose and move strategy was practiced in 33.2% of the sheep flocks. CONCLUSIONS: The present study showed that inaccurate weight calculation gives a risk of under-dosing in over 90% of the sheep and goat flocks in Norway. Taken together with a high treatment frequency in lambs, a lack of anthelmintic class rotation and the common use of a dose-and-move strategy, a real danger for development of anthelmintic resistance (AR) seems to exist in Norwegian sheep and goat flocks. This risk seems particularly high in coastal areas where high treatment frequencies in lambs were recorded.

Individual animal risk factors for clinical mastitis in meat sheep in Norway.

An m:n matched case-control study was conducted to identify risk factors for ovine clinical mastitis (CM). Data were from a national sheep registry and only ewes that lambed in the spring of 2004 were included. Eligible cases (n = 2857) and controls (n = 76,716) from 1056 flocks of meat sheep were matched on flock and conditional logistic regression was used for analysis of the data. CM risk was associated with age of the ewe and whether or not assistance at lambing was needed owing to dystocia; however, the effects of both these factors were modified by the number of lambs born. In ewes with 1 lamb, increasing age was associated with increased odds of CM (OR = 1.2 for each 1-year increase), while only a slight numerical increase in the odds was observed in ewes with >1 lamb. Dystocia was associated with increased odds of CM in ewes with 1 lamb (OR = 1.7) or 2 lambs (OR = 1.4), while no association was observed in ewes with > 2 lambs. The odds of CM increased markedly with increasing number of lambs born to the ewe. For example, odds for 2-year-old ewes without dystocia were 6.7 times greater for those with > 3 lambs than for those with 1 lamb. Compared with ewes of old Norwegian breeds, ewes of other breeds were more likely to experience CM (OR = 1.7). Ewes treated for CM at least once during the preceding 3 years had 4.0 times greater odds of CM compared with ewes without a CM history. It is likely that the effect estimates from this study, which are adjusted for breed and unaffected by inter-flock variations, are valid also for other meat sheep populations.

Norwegian farmers' vigilance in reporting sheep showing scrapie-associated signs.

BACKGROUND: Scrapie is a chronic neurodegenerative disease affecting small ruminants and belongs to the transmissible spongiform encephalopathies. Scrapie is considered a serious animal disease and it has been notifiable in Norway since 1965. The clinical signs of scrapie might be vague and the farmers, if familiar with the signs of scrapie, are often in the best position for detecting scrapie suspects. In 2002, an anonymous questionnaire survey was conducted in order to assess Norwegian sheep farmers' vigilance of scrapie. RESULTS: Although the potential detection of a scrapie-positive animal would lead to the destruction of the sheep flock concerned, almost all the farmers (97 %) expressed their willingness to report scrapie suspects. This was most certainly dependent on the Government taking the economic responsibility for the control programme as nearly all the farmers responded that this was an important condition. Listeriosis is relatively common disease in Norwegian sheep and a differential diagnosis for scrapie. In a multinomial logistic regression the reporting behaviour for non-recovering listeriosis cases, used as a measurement of willingness to report scrapie, was examined. The reporting of non-recovering listeriosis cases increased as the knowledge of scrapie-associated signs increased, and the reporting behaviour was dependent on both economic and non-economic values. CONCLUSION: The results indicate that in 2002 almost all sheep farmers showed willingness to report any scrapie suspects. Nevertheless there is an underreporting of scrapie suspects and the farmers' awareness and hence their vigilance of scrapie could be improved. Furthermore, the results suggest that to ensure the farmers' compliance to control programmes for serious infectious diseases, the farmers' concerns of non-economic as well as economic values should be considered.

Hematologic evaluation of normal and anemic lambs with the Technicon H*1 using EDTA or heparin as anticoagulants.

A study was performed to evaluate blood from young lambs using the Technicon H*1 hematology analyzer, with emphasis on RBC parameters, comparison of tripotassium EDTA and heparin, and the effects of storage on heparinized blood. Blood samples from lambs 2 days to 18 weeks of age were analyzed within 6 hours, revealing a high precision, except for WBC counts in heparinized blood. The HCT values estimated by the H*1 correlated well (r(2)=.90) with those obtained by the microhemotocrit method. Mean hematologic values obtained for heparinized blood differed by up to 4% from values obtained from blood collected into EDTA. WBC counts decreased 8.5% in heparinized blood stored at 4 degrees C for 1 day, but differences observed in RBC counts were