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VLA Quarterly - Schmallenberg Recognised in UK

28 July 2012

As well as cases of Schmallenberg virus (SBV) continuing to be found in the UK, there was an increase in the rate of undiagnosed bovine abortion, possibly associated with increased submissions arising from increased awareness of SBV, according to the Veterinary Laboratory Agency's quarterly report (January to March 2012).

Schmallenberg virus (SBV)

Between August and October 2011, outbreaks of disease in adult cattle that included mild to moderate fever, reduced milk yield, loss of appetite, loss of body condition and diarrhoea were reported in both the Netherlands and Germany. Later, abortions and stillbirths associated with foetal abnormalities, affecting sheep, cattle and goats, were identified in a number of European countries.

A new virus was identified as the cause of both conditions, and the virus was named ‘Schmallenberg virus’ (SBV) after the German town where the virus was first identified. AHVLA and SAC implemented enhanced surveillance for foetal abnormalities caused by SBV and, in January 2012, the first cases of SBV-associated disease in Great Britain were identified by AHVLA by PCR test in sheep in the south east of England. In early February 2012, the AHVLA reported the first PCR-positive cattle sample in Great Britain, in a sample from a farm in West Sussex. By the end of March 2012, SBV infection had been identified by PCR test on 25 cattle holdings in England, across the counties of Cornwall, Devon, East Sussex, Essex, Kent, Norfolk, Suffolk, Surrey, West Sussex and Wiltshire.

All of these counties were at risk of infected midge incursion from mainland Europe during the summer and autumn of 2011. SBV is an Orthobunyavirus; viruses in this genus are typically primarily spread by biting insect vectors, such as midges and mosquitoes.

At the end of the first quarter of 2012, the total number of cattle holdings in Great Britain from which animals or samples had been submitted and tested PCR-positive for SBV remained relatively low (25), however this is likely to be a significant under-representation as there is no statutory requirement to report suspected cases of SBV-associated disease; some reports of suspected SBV disease are telephone reports only; and the PCR test does not identify all cases of SBV.

A Europe-wide assessment has concluded that SBV is unlikely to cause illness in people. http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/EmergingInfections/SchmallenbergVirus/e mergSchmallenbergQandA/

Analysis of Diagnosis Not Reached (DNR) submissions

Overview

During the period January to March 2012, 25% of diagnostic cattle submissions to AHVLA and SAC remained undiagnosed and this is consistent with figures from previous years.

Abortion

An increase in cattle presenting with abortion was reported in the first quarter of 2012. During this period, 53% of cattle presenting with abortion remained undiagnosed compared with 47% in previous years. The figures were statistically significant for data from AHVLA, which covers England and Wales, where the percentage of undiagnosed abortions matched the figures for Great Britain. The increase was greatest in January and decreased to statistically insignificant levels in March. This is shown in Figure 3.

It is possible that the increase in DNR proportion for the presenting sign abortion was related to increased awareness of SBV, and increased interest in investigating sporadic bovine abortions. The diagnostic rate for laboratory investigation of bovine abortion can be low, partly because some cases have a non-infectious aetiology. It is possible that sporadic cases may be more likely to have a noninfectious aetiology. Monitoring of the DNR rate for abortion in cattle will continue over the next quarter.

UNUSUAL DIAGNOSES

E. coli type O4.K infection

An ongoing problem, since October 2011, of diarrhoea in calves in the first two weeks of life in a dairy unit was investigated. Several calves had died. Examination of faeces samples and a carcase submitted for necropsy revealed E. coli type O4.K. This E. coli serotype has an association with a cytotoxic necrotising factor and is associated with bacteraemia, diarrhoea and dysentery in young farm animals. It was also ascertained that there was poor colostral transfer of immunity which probably made the calves more susceptible to the infection.

Toxocara vitulorum

Toxocara vitulorum eggs were identified in the faeces of a young calf in a 150-cow beef suckler herd in the East Midlands, following an episode of diarrhoea. Further sampling identified the parasite’s eggs in one other calf that showed no unusual clinical signs. There was no evidence of a link with other Bos species that are known to be associated with T. vitulorum such as bison or buffalo, or of importation of animals, but the herd had a history of regular buying in of stock from a variety of sources, which could have provided an entry route. Cryptosporidium was also isolated from the calf with diarrhoea, and it was thought that this was the likely cause of the clinical signs rather than T. vitulorum. T vitulorum has a very different epidemiological pattern to the more usual endemic nematode parasites of British cattle, and necessitates specific control measures once it has become established in a herd. Scanning surveillance by AHVLA has detected occasional cases of this parasite in cattle since 2007.

Congenital abnormalities

The enhanced surveillance for SBV conducted during the first quarter of 2012 inevitably resulted in an increased number of submissions of malformed newborn calves. A number of other foetal abnormalities (not associated with SBV infection) were diagnosed during the quarter, including Schistosomus reflexus, microphthalmos, ‘spina bifida’ and Arnold-Chiari malformation.

CHANGES IN DISEASE PATTERNS AND RISK FACTORS

Fasciolosis

Percentage of Scanning Surveillance Submissions in Which Fasciolosis was Diagnosed in Quater 1

The percentage of submissions in which fasciolosis was diagnosed was significantly higher for Scotland than for England and Wales in this quarter. The same trend was seen in the last quarter of 2011. 2011 was the wettest year since 1910 in Scotland. The heavy rainfall and mild temperatures continued in parts of Scotland in January 2012, with 150% of the average in the north, but with greater variation and below average rainfall in the south east and Scottish Borders. Wet and mild weather favours the life cycle of the liver fluke and survival of infective metacercariae on pasture. AHVLA and SAC will continue to highlight liver fluke disease, and the best means of long term control which is planning fluke control as part of a herd health plan.

Infectious Bovine Rhinotracheitis

Incidents of IBR in Cattle as % of Diagnosable Submissions in Quater 1

There was a non-statistically significant reduction in the number of diagnoses of IBR in England and Wales, but not in Scotland, compared to the same quarter in 2011. Many laboratories reported outbreaks of IBR with the primary presentation of conjunctivitis in dairy cows and heifers and in growing suckler cattle. Conjunctivitis is a recognised sign of IBR but is more commonly seen in association with upper respiratory tract signs.

HORIZON-SCANNING

Schmallenberg virus (SBV)

It is possible that SBV will successfully overwinter in Great Britain. If this is the case, it is possible that cases of acute SBV-associated disease will occur during the summer. Some acute clinical signs of SBV infection may be observed in cattle e.g. milk drop, fever and diarrhoea, particularly along the edge of the risk area and most likely in adult dairy cattle.

July 2012

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