Didier Calavas

Comparison of French natural scrapie isolates with bovine spongiform encephalopathy and experimental scrapie infected sheep

We compared the glycoform pattern of the abnormal prion protein (PrP(Sc)) detected by immunoblotting in 21 sheep with natural scrapie, from 21 different outbreaks identified in France since 1996, with a bovine spongiform encephalopathy (BSE)-infected sheep. All the natural scrapie isolates had a higher molecular mass of the unglycosylated PrP(Sc) than in BSE-infected sheep. In the latter case, this molecular mass appeared identical to that found in the CH 1641 experimental scrapie strain (type C pattern), whereas in natural scrapie cases it was similar to that found in the SSBP/1 experimental scrapie strains. These results suggest that all French natural scrapie isolates studied so far would belong, as SSBP/1, to the group of scrapie cases with type A electrophoretic pattern.

Review on the epidemiology and dynamics of BSE epidemics

The paper describes how the comprehensive surveillance of bovine spongiform encephalopathy (BSE) and studies carried out on these data has enhanced our knowledge of the epidemiology of BSE. Around 7, 000 BSE cases were detected through the screening of about 50 million cattle with rapid tests in Europe. It confirmed that the clinical surveillance had a poor capacity to detect cases, and also showed the discrepancy of this passive surveillance efficiency between regions and production types (dairy/beef). Other risk factors for BSE were being in a dairy herd (three times more than beef), having a young age at first calving (for dairy cattle), being autumn-born (dairy and beef), and being in a herd with a very high milk yield. These findings focus the risk on the feeding regimen of calves/heifers. Several epidemiological studies across countries suggest that the feedborne source related to meat and bone meal (MBM) is the only substantiated route of infection - even after the feed ban -, while it is not possible to exclude maternal transmission or milk replacers as a source of some infections. In most European countries, the average age of the cases is increasing over time and the prevalence decreasing, which reflects the effectiveness of control measures. Consistent results on the trend of the epidemic were obtained using back-calculation modelling, the R(0) approach and Age-Period-Cohort models. Furthermore, active surveillance also resulted in the finding of atypical cases. These are distinct from previously found BSE and classified in two different forms based on biochemical characteristics; their prevalence is very low (36 cases up to 1st September 2007), affected animals were old and some of them displayed clinical signs. The origin and possibility of natural transmission is unknown.

Atypical Bovine Spongiform Encephalopathies, France, 2001–2007

In France, through exhaustive active surveillance, ≈17.1 million adult cattle were tested for bovine spongiform encephalopathy from July 2001 through July 2007; ≈3.6 million were >8 years of age. Our retrospective Western blot study of all 645 confirmed cases found that 7 were H-type and 6 were L-type.

Distribution and antimicrobial resistance of clinical and subclinical mastitis pathogens in dairy cows in Rhône-Alpes, France.

The goal of this study was to estimate the distribution of pathogens, as well as their antimicrobial resistance pattern, in cows affected by clinical or subclinical mastitis in the Rhône-Alpes region of France. A total of 1770 samples were taken between January 2007 and March 2008, leading to the identification of 1631 bacterial isolates. Streptococcus uberis (22.1%), Escherichia coli (16%), and coagulase-positive staphylococci (15.8%) were identified as the major causative agents of clinical mastitis, whereas coagulase-positive staphylococci (30.2%), coagulase-negative staphylococci (13.7%), and Streptococcus dysgalactiae (9.3%) were predominantly implicated in subclinical mastitis. Yet, in both types of mastitis, about 20% of all cases were due to a large number of different bacterial species that were isolated at a low frequency (<5%), which cannot be considered as minor (e.g., Klebsiella spp.) or noncontagious (e.g., Corynebacterium spp.). The overall proportion of antibiotic resistance was low, except for penicillin G in staphylococci, as well as for macrolides and tetracycline in streptococci. Yet, these resistance proportions were much lower than those reported in human medicine. Besides providing up-to-date information on mastitis in France, this survey also indicates the prudent use of antibiotics by veterinarians. As a result, this study suggests that the risk of transmission of resistant bacteria from milk or milk products to human is very limited, even in case of consumption of raw milk. However, it also confirms the fact that attention must be maintained to avoid any emergence of such resistant bacteria.

Epidemiology, molecular virology and diagnostics of Schmallenberg virus, an emerging orthobunyavirus in Europe

After the unexpected emergence of Bluetongue virus serotype 8 (BTV-8) in northern Europe in 2006, another arbovirus, Schmallenberg virus (SBV), emerged in Europe in 2011 causing a new economically important disease in ruminants. The virus, belonging to the Orthobunyavirus genus in the Bunyaviridae family, was first detected in Germany, in The Netherlands and in Belgium in 2011 and soon after in the United Kingdom, France, Italy, Luxembourg, Spain, Denmark and Switzerland. This review describes the current knowledge on the emergence, epidemiology, clinical signs, molecular virology and diagnosis of SBV infection.

Mycoplasmoses of ruminants in France: recent data from the national surveillance network

BackgroundRuminant mycoplasmoses are important diseases worldwide and several are listed by the World Organization for Animal Health to be of major economic significance. In France the distribution of mycoplasmal species isolated from clinical samples collected from diseased animals upon veterinary request, is monitored by a network known as VIGIMYC (for VIGIlance to MYCoplasmoses of ruminants). The veterinary diagnostic laboratories collaborating with VIGIMYC are responsible for isolating the mycoplasmas while identification of the isolates is centralized by the French Food Safety Agency (AFSSA) in Lyon. The VIGIMYC framework can also be used for specific surveys and one example, on the prevalence of M. bovis in bovine respiratory diseases, is presented here.ResultsBetween 2003 and 2008, 34 laboratories were involved in the network and 1904 mycoplasma isolates, originating from the main ruminant-breeding areas, were identified. For cattle, the high prevalence of M. bovis in bronchopneumonia, notably in young animals, was confirmed by VIGIMYC and an associated specific survey, whereas the non-emergence of species such as M. alkalescens and M. canis was also demonstrated. The etiological agent of bovine contagious pleuropneumonia was never isolated. The principal mycoplasmosis in goats was contagious agalactia with M. mycoides subsp. capri as main agent. Ovine mycoplasmoses, most of which were associated with pneumonia in lambs, were infrequently reported. One exception was ovine contagious agalactia (due to M. agalactiae) that has recently re-emerged in the Pyrénées where it had been endemic for years and was also reported in Corsica, which was previously considered free.ConclusionsAlthough VIGIMYC is a passive network and somewhat biased as regards sample collection and processing, it has provided, in this study, an overview of the main mycoplasmoses of ruminants in France. The French epidemiological situation is compared to those existing elsewhere in the world.

Molecular analysis of the protease-resistant prion protein in scrapie and bovine spongiform encephalopathy transmitted to ovine transgenic and wild-type mice.

ABSTRACT The existence of different strains of infectious agents involved in scrapie, a transmissible spongiform encephalopathy (TSE) of sheep and goats, remains poorly explained. These strains can, however, be differentiated by characteristics of the disease in mice and also by the molecular features of the protease-resistant prion protein (PrPres) that accumulates into the infected tissues. For further analysis, we first transmitted the disease from brain samples of TSE-infected sheep to ovine transgenic [Tg(OvPrP4)] and to wild-type (C57BL/6) mice. We show that, as in sheep, molecular differences of PrPres detected by Western blotting can differentiate, in both ovine transgenic and wild-type mice, infection by the bovine spongiform encephalopathy (BSE) agent from most scrapie sources. Similarities of an experimental scrapie isolate (CH1641) with BSE were also likewise found following transmission in ovine transgenic mice. Secondly, we transmitted the disease to ovine transgenic mice by inoculation of brain samples of wild-type mice infected with different experimental scrapie strains (C506M3, 87V, 79A, and Chandler) or with BSE. Features of these strains in ovine transgenic mice were reminiscent of those previously described for wild-type mice, by both ratios and by molecular masses of the different PrPres glycoforms. Moreover, these studies revealed the diversity of scrapie strains and their differences with BSE according to labeling by a monoclonal antibody (P4). These data, in an experimental model expressing the prion protein of the host of natural scrapie, further suggest a genuine diversity of TSE infectious agents and emphasize its linkage to the molecular features of the abnormal prion protein.

Preliminary estimate of Schmallenberg virus infection impact in sheep flocks – France

Schmallenberg virus (SBV) infection is an emerging livestock disease caused by a novel Orthobunyavirus which was first identified in Germany in November 2011. Non-specific clinical signs such as fever, decreased milk production and diarrhoea are associated with the acute infection in cattle, while late abortions and birth defects in newborns can be associated with the infection of pregnant cows, ewes and goats (Hoffmann and others 2012, Van den Brom and others 2012). As of March 30, 2012, since the first identification of congenital forms of SBV virus infection in The Netherlands in December 2011, about 3000 confirmed outbreaks have been reported in eight European countries (Belgium, France, Germany, Italy, Luxembourg, The Netherlands, Spain, UK) (French National Surveillance Platform for Animal Health 2012). However, little is known about SBV virus infection, especially with regard to its clinical impact in the affected herds. SBV emergence is closely monitored in France. Farmers are urged to contact their veterinarian when encountering cases of ruminant neonates or fetuses stillborn, malformed or showing nervous disorders. A brain sample is collected on any newborn suspected of congenital SBV until a first confirmation of the infection is obtained for the herd. An SBV diagnostic test is performed in state diagnostic laboratories, using real-time quantitative reverse transcription PCR (RT-qPCR). The first cases of SBV virus infection were …

Serological prevalence of Mycoplasma bovis infection in suckling beef cattle in France.

The prevalence of Mycoplasma bovis infection in France was assessed by means of a serological survey of suckling beef cattle, using an ELISA. The survey included 824 randomly selected herds in eight French counties and a total of 32,197 animals more than one year old. In each county, the number of herds tested was determined statistically on the basis of the hypothesis that about 40 per cent of herds are infected. The proportion of herds containing at least one infected animal ranged from 28 to 90 per cent depending on the county. Among the 32,197 sera tested, the animal infection rate ranged between 2 per cent and 13 per cent. In infected herds, the average number of positive animals per herd was between 10 and 20 per cent, and the infection was unevenly distributed among the areas tested.

Why do farmers and veterinarians not report all bovine abortions, as requested by the clinical brucellosis surveillance system in France?

BackgroundSince 2005, France has been officially free of brucellosis, an infectious disease that causes abortion in cattle and can be transmitted from cattle to humans. Recent animal and human cases have drawn attention to the need to prevent infection of humans and animals from any primary outbreaks. In order to detect any new outbreaks as soon as possible, a clinical surveillance system requires farmers and veterinarians to report each abortion and to test the aborting cow for brucellosis. However, under-reporting limits the sensitivity of this system. Our objective was to identify the barriers and motivations influencing field actors in their decision to report or not to report bovine abortions. We used a qualitative approach with semi-structured interviews of 12 cattle farmers and their eight veterinarians.ResultsOur analysis showed that four main themes influence the decision-making process of farmers and veterinarians: 1) the perceived risk of brucellosis and other abortive diseases; 2) the definition of a suspected case of brucellosis and other abortive diseases adopted by field actors, which is less sensitive than the mandatory definition; 3) the cost-benefit analysis conducted by actors, taking into account regulatory and health aspects, economic and financial losses, technical and practical factors; 4) the level of cooperation within the socio-technical network. We discussed how early detection may be improved by revising the definition of abortion, extending the time frame for notification and generalising the differential diagnosis of the causes of abortion.ConclusionsIn contrast to quantitative approaches, qualitative studies can identify the factors (including unknown factors) influencing the decision-making process of field actors and reveal why they take those factors into consideration. Our qualitative study sheds light on the factors underlying the poor sensitivity of clinical brucellosis surveillance system for cattle in France, and suggests that early detection may be improved by considering actors’ perceptions. We believe our findings may provide further insight into ways of improving other clinical surveillance systems and thus reduce the risk of disease.