M. Elvander

Severe respiratory disease in dairy cows caused by infection with bovine respiratory syncytial virus

Outbreaks of severe respiratory disease caused by bovine respiratory syncytial virus (BRSV) were recorded in dairy herds throughout Sweden in 1988 and subsequently. The virus was demonstrated in nasopharyngeal swab material from animals in the acute stage of the disease by culture, the polymerase chain reaction (PcR) and by immunofluorescence. Serological data from the herds investigated showed that the cows had seroconverted to BRSV rather than to bovine coronavirus, bovine viral diarrhoea virus or parainfluenza-3 virus. It was predominantly dairy herds in isolated areas that contracted a severe primary BRSV infection, often after the purchase of new animals. A nationwide survey for BRSV antibodies in bulk milk samples showed the highest prevalence, of 84 to 89 per cent, in the southernmost regions of Sweden and the lowest prevalence, of 41 to 51 per cent, in the north of the country. The prevalence of BRSV was highest in areas with the highest populations of cattle.

Causes of Stillbirth and Time of Death in Swedish Holstein Calves Examined Post Mortem

This study was initiated due to the observation of increasing and rather high levels of stillbirths, especially in first-calving Swedish Holstein cows (10.3%, 2002). Seventy-six Swedish Holstein calves born to heifers at 41 different farms were post mortem examined in order to investigate possible reasons for stillbirth and at what time in relation to full-term gestation they had occurred. The definition of a stillborn calf was dead at birth or within 24 h after birth after at least 260 days of gestation. Eight calves were considered as having died already in uterus. Slightly less than half of the examined calves (46.1%) were classified as having died due to a difficult calving. Four calves (5.3%) had different kinds of malformations (heart defects, enlarged thymus, urine bladder defect). Approximately one third of the calves (31.6%) were clinically normal at full-term with no signs of malformation and born with no indication of difficulties at parturition or any other reason that could explain the stillbirth. The numbers of male and female calves were rather equally distributed within the groups. A wide variation in post mortem weights was seen in all groups, although a number of the calves in the group of clinically normal calves with unexplained reason of death were rather small and, compared with e.g. those calves categorised as having died due to a difficult calving, their average birth weight was 6 kg lower (39.9 ± 1.7 kg vs. 45.9 ± 1.5 kg, p ≤ 0.01). It was concluded that the cause of stillbirth with a non-infectious aetiology is likely to be multifactorial and difficult calving may explain only about half of the stillbirths. As much as one third of the calves seemed clinically normal with no obvious reason for death. This is a target group of calves that warrants a more thorough investigation in further studies.SammanfattningObduktionsstudie av dödfödda SLB-kalvar - dödsorsaker och dödstidpunkt.Andelen dödfödda kalvar har ökat och den genomsnittliga frekvensen hos förstakalvande SLB är nu 10.3% (2002). Detta utgjorde bakgrunden till att denna studie initierades där 76 dödfödda SLB-kalvar från förstakalvare i 41 olika besättningar obducerades med syfte att fastställa dödsorsak samt tidpunkt i förhållande till födseln. Definitionen av en dödfödd kalv var att den efter fullgången dräktighet (minst 260 dagar) var död vid födseln eller inom 24 timmar efter födseln. Åtta kalvar (10,5%) bedömdes ha dött redan i livmodern. Knappt hälften av kalvarna (46,1%) bedömdes ha dött på grund av svår kalvning. Fyra kalvar (5,3%) hade olika typer av missbildningar (2 hjärtmissbildningar, 1 förstorad thymus, 1 urinblåsedefekt). Nära en tredjedel av kalvarna (31,6%) var fullt utvecklade och utan några tecken på missbildningar, kalvningssvårigheter eller andra or saker som kunde förklara dödfödseln. Fördelningen av tjur- resp. kvigkalvar inom de olika kategorierna var i stort sett lika. Variationen i födelsevikter var stor inom alla kategorier, men den genomsnittliga födelsevikten var ca 6 kilo lägre för den tredjedel kalvar som föddes fullt utvecklade med oförklarad dödsorsak. Det konkluderades att orsaken till dödfödslar (med en icke-infektiös sjukdomshistoria) är multifaktoriell och att svåra kalvningar bara förklarar cirka hälften av dödfödslarna. Att det hos en så stor andel som en tredjedel av kalvarna tycks finnas någon form av oförklarat vitalitetsproblem gör att orsakerna till dödsfallen för denna grupp av kalvar behöver studeras ytterligare i framtida studier.

Possible means of introduction of bluetongue virus serotype 8 (BTV-8) to Sweden in August 2008: comparison of results from two models for atmospheric transport of the Culicoides vector.

In September 2008, bluetongue virus serotype 8 (BTV-8) infection was detected for the first time in Sweden, in a dairy herd on the west coast. Two different previously published operational atmospheric dispersion models indicate that midges from infected regions in Europe are likely to have reached Sweden by atmospheric transport during an estimated infection window. Both models indicated that the likely dates for the incursion of midges were overnight on August 6 to 7 and August 14 to 15; however, the less constrained model indicated a number of additional possible dates. The distribution of infected herds detected by active surveillance coincides with the regions that were indicated by the models to have been reached by midges from regions in Denmark and Germany with infected herds. It is likely that several points of introduction of infected midges occurred, possibly on different occasions. No alternative routes for introduction of the infection to Sweden were identified, supporting the theory that BTV-8 was introduced by infected midges carried by the wind.

Anthrax outbreak in a Swedish beef cattle herd - 1st case in 27 years: Case report

After 27 years with no detected cases, an outbreak of anthrax occurred in a beef cattle herd in the south of Sweden. The outbreak was unusual as it occurred in winter, in animals not exposed to meat-and-bone meal, in a non-endemic country.The affected herd consisted of 90 animals, including calves and young stock. The animals were kept in a barn on deep straw bedding and fed only roughage. Seven animals died during 10 days, with no typical previous clinical signs except fever. The carcasses were reportedly normal in appearance, particularly as regards rigor mortis, bleeding and coagulation of the blood. Subsequently, three more animals died and anthrax was suspected at necropsy and confirmed by culture and PCR on blood samples.The isolated strain was susceptible to tetracycline, ciprofloxacin and ampicillin. Subtyping by MLVA showed the strain to cluster with isolates in the A lineage of Bacillus anthracis.Environmental samples from the holding were all negative except for two soil samples taken from a spot where infected carcasses had been kept until they were picked up for transport.The most likely source of the infection was concluded to be contaminated roughage, although this could not be substantiated by laboratory analysis. The suspected feed was mixed with soil and dust and originated from fields where flooding occurred the previous year, followed by a dry summer with a very low water level in the river allowing for the harvesting on soil usually not exposed. In the early 1900s, animal carcasses are said to have been dumped in this river during anthrax outbreaks and it is most likely that some anthrax spores could remain in the area.The case indicates that untypical cases in non-endemic areas may be missed to a larger extent than previously thought. Field tests allowing a preliminary risk assessment of animal carcasses would be helpful for increased sensitivity of detection and prevention of further exposure to the causative agent.

Infection with bluetongue virus serotype 8 in Sweden in 2008

On September 6, 2008, bluetongue was detected for the first time in Sweden. Intensified active surveillance in cattle and vector surveillance, prompted by the situation in northern Europe, preceded the detection. A vaccination campaign and intensive surveillance activities were initiated nationally, but with a focus on the southern part of the country. Measures included both active and passive surveillance by serology and PCR in ruminants, along with vector surveillance. The investigations revealed that the infection occurred over a large area of southern Sweden during September and October 2008, despite comparatively low vector activity, an apparently low viral load and no clinical disease. Transplacental infection was detected in one case.

Risk of introduction of BSE into Sweden by import of cattle from the United Kingdom

All cattle of United Kingdom origin imported to Sweden since 1980 were traced (n=94) and the probability that none of these imported cattle had clinical signs of bovine spongiform encephalopathy (BSE) at the year of slaughter (death) was calculated. If BSE had been introduced by live-animal imports, the consequences of such an event also was evaluated. The potential of the recently introduced surveillance system of high-risk cattle to detect such an event also was evaluated. We found that BSE most probably has not been introduced to Sweden by live-animal imports. We also found that, if this event had occurred and assuming a worst-case scenario that the animal was not prevented from being rendered, the rendering system (during certain periods) would not have prevented further spread of infection. Finally, we found that the BSE surveillance of high-risk cattle has not been in place long enough to verify that this event has not occurred (as of December 2001).

Strong protection induced by an experimental DIVA subunit vaccine against bluetongue virus serotype 8 in cattle

Bluetongue virus (BTV) infections in ruminants pose a permanent agricultural threat since new serotypes are constantly emerging in new locations. Clinical disease is mainly observed in sheep, but cattle were unusually affected during an outbreak of BTV seroype 8 (BTV-8) in Europe. We previously developed an experimental vaccine based on recombinant viral protein 2 (VP2) of BTV-8 and non-structural proteins 1 (NS1) and NS2 of BTV-2, mixed with an immunostimulating complex (ISCOM)-matrix adjuvant. We demonstrated that bovine immune responses induced by this vaccine were as good or superior to those induced by a classic commercial inactivated vaccine. In this study, we evaluated the protective efficacy of the experimental vaccine in cattle and, based on the detection of VP7 antibodies, assessed its DIVA compliancy following virus challenge. Two groups of BTV-seronegative calves were subcutaneously immunized twice at a 3-week interval with the subunit vaccine (n=6) or with adjuvant alone (n=6). Following BTV-8 challenge 3 weeks after second immunization, controls developed viremia and fever associated with other mild clinical signs of bluetongue disease, whereas vaccinated animals were clinically and virologically protected. The vaccine-induced protection was likely mediated by high virus-neutralizing antibody titers directed against VP2 and perhaps by cellular responses to NS1 and NS2. T lymphocyte responses were cross-reactive between BTV-2 and BTV-8, suggesting that NS1 and NS2 may provide the basis of an adaptable vaccine that can be varied by using VP2 of different serotypes. The detection of different levels of VP7 antibodies in vaccinated animals and controls after challenge suggested a compliancy between the vaccine and the DIVA companion test. This BTV subunit vaccine is a promising candidate that should be further evaluated and developed to protect against different serotypes.

Immunological diagnosis of encephalitozoonosis from post-mortem specimens

Abstract Antibody to Encephalitozoon cuniculi for immunopathological diagnosis was obtained from organs and fluids from rabbit carcasses. By the use of the india-ink immunoreaction antibodies to E. cuniculi were detected in lungs, kidneys and pleural fluid of seropositive animals. Mean values of the antibody titres in the lungs were 1 10 to 1 2 of that in serum. Antibody titres from other organs were inconsistent. No titres were found in organs or fluids from seronegative rabbits.

Risk assessment as a tool for improving external biosecurity at farm level

BackgroundBiosecurity routines at herd level may reduce the probability of introduction of disease into the herd, but some measures may be regarded as expensive and cumbersome for the farmers. Custom-made measures based on individual farm characteristics may aid in improving the actual application of on-farm biosecurity.The aim of the study was to provide a tool for calculating the effects of different biosecurity measures and strategies on the individual farm level.A simple model was developed to assess the risk of disease introduction and the need for biosecurity measures in individual farms. To illustrate the general applicability of the tool, it was applied to theoretical examples of Swedish cattle and pig farms and diseases endemic in those animal species in the EU, in two scenarios with different between-farm contact patterns.ResultsThe model illustrated that the most important factors affecting the risk, and the effect of biosecurity measures such as quarantine routines and protective clothing, were the frequency of between-farm contacts and prevalence of the disease. The risk of introduction as well as the effect of biosecurity measures differed between farm types and disease transmission routes. Adapting contact patterns to mitigate a specific disease risk was as important as biosecurity measures for some farm types, but the largest effect was seen when combining biosecurity measures with more planned contact patterns.ConclusionsThe risk assessment model proved useful for illustrating the risk of introduction of endemic diseases and the mitigating effect of different biosecurity measures on farm level. Model outputs could be used to justify prioritisation of measures or adapting contact patterns. The theoretic exercise of adjusting model inputs and comparing outputs may help veterinary advisors to understand farm-specific risks and motivate farmers to improve biosecurity in their individual farm, as it can be tailored to each farmer’s needs and preferences.

Detection of IgM responses to bovine respiratory syncytial virus by indirect ELISA following experimental infection and reinfection of calves: abolition of false positive and false negative results by pre-treatment of sera with protein-G agarose.

Abstract The IgM responses in three panels of sera generated by infection and reinfection of calves with bovine respiratory syncytial virus (BRSV) were measured by indirect ELISA (I-ELISA). The effect of depleting serum IgG by pre-treatment with protein G agarose (PGA) was evaluated. Following primary infection a weak IgM response was detected in the untreated sera of 3 out of 4 calves with maternally derived antibody (MDA). Both the magnitude and duration of the specific IgM responses in these calves were increased by pre-treatment with PGA. In addition, the fourth infected calf tested gave a single positive IgM result following PGA treatment. Transient or persistent IgM responses which were abolished by pre-treatment of sera with PGA were detected in 4/8 calves following reinfection. These were considered to be false positive results, consistent with the influence of IgM rheumatoid factor (IgM-RF). One of these calves and two additional calves showed transient increases in IgM which were resistant to PGA treatment. These were considered to represent specific IgM responses to reinfection. The results indicate the ability of PGA treatment to eliminate both false positive and false negative results and emphasise the necessity for controlling the influence of IgM-RF in IgM-specific indirect ELISAs.