Seasonal differences in cytokine expression in the skin of Shetland ponies suffering from insect bite hypersensitivity.

Insect bite hypersensitivity (IBH) in horses is a seasonal, IgE-mediated, pruritic skin disorder primarily caused by Culicoides spp. We hypothesize that a mixed Th2/Th1-type immune status, off season, alters into Th2-dominated immune reactivity in the skin of IBH-affected ponies in the IBH season. To study these immune response patterns Culicoides-specific IgE levels, skin histopathology and cytokine and transcription factor mRNA expression (IL4, IL10, IL13, IFNγ, FoxP3 and CD3(ζ)) in lesional and non-lesional skin of ponies affected by IBH in the IBH season were compared with those of the same animals off season and those in skin of healthy ponies in both seasons. The present study revealed a significantly higher histopathology score in lesional skin of affected ponies than in non-lesional skin and skin of healthy ponies in the IBH season. Culicoides obsoletus-specific IgE serum levels of ponies with IBH were significantly higher than those in healthy ponies in both seasons. Interestingly, C. obsoletus-specific IgE serum levels within each group were the same in the IBH season and off season. The expression of IL4, IL13 and IFNγ mRNA in skin biopsies in the IBH season showed a significant increase compared to off season in both skin derived from healthy control ponies (n=14) as well as in lesional and in non-lesional skin from IBH-affected animals (n=17). This apparently general up-regulation of cytokine expression during the IBH season directly correlated with an increased CD3(ζ) mRNA expression in the skin, indicating an overall increased T cell influx during the summer months. The only significant difference observed between lesional skin from IBH-affected animals as compared to skin from healthy control animals in the IBH season was a lower expression of IL13/CD3(ζ) in the affected animals. FoxP3 and IL10 levels were unaffected, except for a lower expression of FoxP3 in healthy control skin in the IBH season as compared to off season, In addition, the increased level of C. obsoletus-specific IgE did not correlate with higher histological scores in LE skin. In summary, our data indicate a general immune activation in the skin of both healthy and IBH-affected ponies during the IBH season that potentially obscures the Culicoides-specific immune reaction pattern, even in lesional skin of IBH-affected animals.

Tracing systems used during the epidemic of classical swine fever in the Netherlands, 1997-1998.

Any outbreak of an animal disease classified as a List A disease by the Office International des Epizooties, such as classical swine fever (CSF), has severe consequences for animal welfare, livestock production, exports of animals and animal products and the environment. Experience shows that early detection and response to a suspected disease outbreak will maximise the effectiveness of the emergency response actions and minimise the social, economic and environmental costs associated with the outbreak. The development and implementation of measures designed to minimise the risk of diseases entering a country or region has been the predominant animal health management strategy in most countries. However, even the strongest preventive management systems do not guarantee that outbreaks of animal diseases will not occur. Tracing, a procedure that begins with a known infected individual, herd or flock, and which traces all possible locational and interactive exposures in both directions, back towards the source and forward to contacts, is the backbone of disease emergency management. The authors provide an introduction to, and general overview of, tracking and tracing systems used during a recent epidemic of CSF in the Netherlands from 1997 to 1998.

Transmission of classical swine fever virus by artificial insemination during the 1997-1998 epidemic in The Netherlands: a descriptive epidemiological study.

In the course of the 1997-1998 CSF epidemic in the Netherlands, two semen collection centres (SCC) became infected. As an eradication strategy for an acute crisis situation, it was concluded that all semen of the boars at the SCCs collected and distributed in the risk period of 28 January to 7 March 1997 was potentially contaminated (suspect semen). As a consequence, a total of 1,680 pig herds, mainly located in the southern part of the Netherlands, were officially declared CSF suspect. The purpose of this study was to investigate whether infection of farms through contaminated semen played a significant role in the CSF epidemic. A total of 123 CSFV infected herds were identified, that had received suspect semen from one or both of the infected SCCs. In 87 out of these 123 infected herds, infection by way of artificial insemination (AI) could be excluded either according to the insemination information or the infection pattern observed. In only 21 herds, infection by way of AI was regarded as possible according to the insemination information and infection pattern. Owing to missing information, no conclusion could be drawn about the possibility of infection of 15 farms by way of AI. Thus, we conclude that at most 36 farms may have been infected through AI during the CSF epidemic in the Netherlands.

The 1997-1998 epidemic of classical swine fever in the Netherlands.

In 1997, the pig husbandry in the Netherlands was struck by a severe epidemic of classical swine fever (CSF). During this epidemic 429 CSF-infected herds were depopulated and approximately 1300 herds were slaughtered pre-emptively. In addition millions of pigs of herds not CSF-infected were killed for welfare reasons (over crowding or overweight). In this paper, we describe the course of the epidemic and the measures that were taken to control it. The first outbreak was detected on 4 February 1997 in the pig dense south-eastern part of the Netherlands. We estimate that CSF virus (CSFV) had already been present in the country by that time for 5-7 weeks and that the virus had been introduced into approximately 39 herds before the eradication campaign started. This campaign consisted of stamping-out infected herds, movement restrictions and efforts to diagnose infected herds as soon as possible. However, despite these measures the rate at which new outbreaks were detected continued to rise. The epidemic faded out only upon the implementation of additional measures such as rapid pre-emptive slaughter of herds in contact with or located near infected herds, increased hygienic measures, biweekly screening of all herds by veterinary practitioners, and reduction of the transportation movements for welfare reasons. The last infected herd was depopulated on 6 March 1998.

The involvement of the agriculture industry and government in animal disease emergencies and the funding of compensation in western Europe.

In Western Europe, the control and eradication of contagious animal diseases have always been subject to government legislation. In the event of an outbreak, the principal policy is 'stamping-out' (depopulation) of the infected herd. The owner of the herd is usually awarded financial compensation. The authors provide an overview of the involvement of the agriculture industry and government in animal disease emergencies and the funding of compensation in Western Europe. In particular, developments within the European Union are described, as illustrated by a case study in the Netherlands. The economic consequences of a widespread epidemic of classical swine fever (hog cholera) in the Netherlands in 1997 are described. Evaluation of the epidemic demonstrated that special emphasis needs to be placed on factors such as the high-risk period, animal movement, the attitude of farmers towards risk and the structure of compensation. Epidemic disease insurance schemes are considered to be a possible alternative in alleviating certain financial losses caused by disease outbreaks.

Classical swine fever in The Netherlands 1997-1998: a description of organisation and measures to eradicate the disease.

The central and regional organisation of the campaign to eradicate the CSF epidemic in The Netherlands in 1997/1998 is described. The main instruments used in the campaign were based on stamping-out and movement restrictions specified by the European Union. Additional instruments were used for the first time, namely, pre-emptive culling of contact and neighbouring farms, compartmentalisation of transport, monthly serological screening in established surveillance areas and supervised repopulation of all farms in the former surveillance zone. Two other measures, the killing of very young piglets and a breeding ban were introduced to reduce production in established surveillance zones. Several factors complicated the eradication campaign, for instance, the late detection of the first infection; artificial insemination as a source of infection; the organisation of pig farming in The Netherlands, with its highly concentrated production and dependence on the transport of stock from one unit to another; insufficient rendering capacity; decreasing sensitivity of clinical inspection; and extremely high costs.

The classical swine fever epidemic 1997-1998 in The Netherlands: descriptive epidemiology.

The objective of this paper is to describe the severe epidemic of classical swine fever (CSF) in The Netherlands in 1997-1998 under a policy of non-vaccination, intensive surveillance, pre-emptive slaughter and stamping out in an area which has one of the highest pig and herd densities in Europe. The primary outbreak was detected on 4 February 1997 on a mixed sow and finishing pig herd. A total of 429 outbreaks was observed during the epidemic, and approximately 700,000 pigs from these herds were slaughtered. Among these outbreaks were two artificial insemination centres, which resulted in a CSF-suspect declaration of 1680 pig herds (mainly located in the southern part of The Netherlands). The time between introduction of CSF virus (CSFV) into the country and diagnosis of CSF in the primary outbreak was estimated to be approximately 6 weeks. It is presumed that CSFV was spread from The Netherlands to Italy and Spain via shipment of infected piglets in the beginning of February 1997, before the establishment of a total stand-still of transportation. In June 1997, CSFV is presumed to be introduced into Belgium from The Netherlands. Pre-emptive slaughter of herds that had been in contact with infected herds or were located in close vicinity of infected herds, was carried out around the first two outbreaks. However, this policy was not further exercised till mid-April 1997, when pre-emptive slaughter became a standard operational procedure for the rest of the epidemic. In total, 1286 pig herds were pre-emptively slaughtered. (approximately 1.1 million pigs). A total of 44 outbreaks (10%) was detected via pre-emptive slaughter. When there were clinical signs, the observed symptoms in infected herds were mainly atypical: fever, apathy, ataxia or a combination of these signs. In 322 out of 429 outbreaks (75%), detection was bases on clinical signs observed: 32% was detected by the farmer, 25% by the veterinary practitioner, 10% of the outbreaks by tracing teams and 8% by screening teams of the veterinary authorities. In 76% of the outbreaks detected by clinical signs, the farmer reported to have seen clinical symptoms for less than 1 week before diagnosis, in 22% for 1-4 weeks before diagnosis, and in 4 herds (1%) the farmer reported to have seen clinical symptoms for more than 4 weeks before diagnosis. Transportation lorries played a major role in the transmission of CSFV before the primary outbreak was diagnosed. It is estimated that approximately 39 herds were already infected before the first measures of the eradication campaign came into force. After the first measures to stop the spread of CSFV had been implemented, the distribution of the most likely routes of transmission markedly changed. In most outbreaks, a neighbourhood infection was indicated. Basically, there were two reasons for this catastrophe. Firstly, there was the extent of the period between introduction of the virus in the region and detection of the first outbreak. As a result, CSFV had opportunities to spread from one herd to another during this period. Secondly, the measures initially taken did not prove sufficient in the swine- and herd-dense region involved.

Quantification of the transmission of classical swine fever virus between herds during the 1997-1998 epidemic in The Netherlands.

In this study, we describe a method to quantify the transmission of Classical Swine Fever Virus (CSFV) between herds from data collected during the 1997-1998 epidemic in The Netherlands. From the contacts between infected herds and the serological findings shortly before depopulation, we estimated the week of virus introduction and the length of the period over which the herd emitted virus for each CSFV-infected herd. From these data, we estimated the infection-rate parameter beta (the average number of herds infected by one infectious herd during one week) and the herd reproduction ratio, Rh (the average total number of secondary outbreaks caused by one infectious herd, i.e. in its entire infectious period), using a SIR-model for different sets of CSF control measures. When Rh > 1, an epidemic continues to grow. On the other hand, when Rh < 1 an epidemic will fade out. During the phase before the first outbreak was diagnosed and no specific measures had been implemented, beta was estimated at 1.09 and Rh at 6.8. In the subsequent phase infected herds were depopulated, movement restrictions were implemented, infected herds were traced forward and backward and the herds in the protection and surveillance zones were clinically inspected by the veterinary authorities (regional screening). This set of measures significantly reduced beta to 0.38. However, Rh was 1.3 and thus still > 1. Consequently, the number of outbreaks continued to grow. After a number of additional measures were implemented, the value of Rh was reduced to 0.5 and the epidemic came to an end. These measures included pre-emptive slaughter of herds that had been in contact with infected herds or were located near an infected herd, increased hygienic procedures, replacement of transports of pigs for welfare reasons by killing of young piglets and a breeding ban, and regional screening for CSF-infected herds by local veterinary practitioners.