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Enzootic bovine leukosis: Report of eradication and surveillance measures in Italy over an 8-year period (2005–2012)

https://doi.org/10.1016/j.prevetmed.2015.02.024Get rights and content

Highlights

  • We found that EBL has been eradicated from most Italian regions.

  • The decreasing trend in BLV is largely attributed to the control measures applied.

  • Implementation of the eradication programme is particularly difficult in some regions.

Abstract

Bovine leukaemia virus (BLV) is associated with enzootic bovine leukosis (EBL). BLV causes malignant lymphoma and lymphosarcoma; however, most BLV infections remain clinically silent in an aleukaemic state. EBL is a notifiable disease, and official control measures include screening or monitoring, precautions at borders, control of movement inside the country, and stamping out.

The objective of this study was to evaluate EBL eradication and surveillance measures in Italy from 2005 to 2012. One-hundred twenty-three outbreaks were recorded (1 January 2006 to 31 December 2012) in the National Veterinary Information System (SIMAN) on 7 November 2013. Of these, 101 had occurred in southern Italy. An outbreak usually lasted for a few days, but sometimes lasted for weeks. Some areas were subjected to normal eradication measures, whereas others were subjected to additional eradication measures as a consequence of persisting EBL outbreaks. During the study period, we noted an overall annual decrease from 0.21% in 2005 to 0.08% in 2012 in the herd prevalence rate, from 0.06% in 2005 to 0.04% in 2012 in the herd incidence rate, and from 0.027% in 2005 to 0.015% in 2012 in the animal prevalence rate. Regions officially recognised as EBL-free areas were found to have their own surveillance plans. Differences in their surveillance plans include the type of sample (serum, milk, or both), age at which the animals must be tested (12 or 24 months), and test frequency of herds (annually or every 2, 3, 4, 5, or 6 years). The eradication programme for EBL is difficult to implement in some Italian areas because of several factors such as incomplete herd registry, geographical location and socio-economic conditions of the region.

Introduction

Bovine leukaemia virus (BLV), an exogenous retrovirus, belongs to a family of oncogenic viruses, which includes human T-lymphotropic viruses 1 and 2 (HTLV-1, HTLV-2), and simian T-cell leukaemia virus 1 and 2; these retroviruses share a common genomic and structural organisation. BLV is associated with enzootic bovine leukosis (EBL), a disease characterised by a very extended course. BLV can be vertically or horizontally transmitted through the transfer of infected cells via several potential routes. One of the major routes of horizontal transmission is by direct contact of mucosal surfaces or broken skin, through a mixture of blood, exudates, and tissues (Hopkins and Di Giacomo, 1997). Furthermore, BLV can be horizontally transmitted through the transfer of infected cells by bites of insects, such as stable flies, Stomoxys calcitrans (Buxton et al., 1985, Ooshiro et al., 2013). Under natural conditions, the disease occurs only in cattle, but sheep are also susceptible to experimental infection (Rola and Kuzmak, 2002); moreover, cases of natural and experimental infection, with low epidemiological impact, have been reported in water buffalo (Persechino et al., 1983). BLV causes malignant lymphoma and lymphosarcoma, but most BLV infections remain clinically silent in an aleukaemic state; approximately one-third of infected cattle develop persistent lymphocytosis, and 5–10% develop lymphoid tumours (Ghysdael et al., 1984). Clinical signs of malignant lymphoma become evident as the tumours invade different tissues.

In herds affected by EBL, economic losses due to death, slaughter, veterinary services, and decreased milk production may be severe (Pelzer, 1997, Sorensen and Beal, 1979, Johnson et al., 1985, Ott et al., 2003;). Furthermore, persistent immunodeficiency and increased susceptibility to other diseases have been reported (Acaite et al., 1999, VanLeeuwen et al., 2001, Chi et al., 2002, Ott et al., 2003).

EBL is prevalent in cattle-raising countries worldwide. It was first reported in Germany in 1874, and it is assumed that it originated in the coastal East Baltic countries. From there, through the trade of live animals, it spread to the American continent during the first half of the 20th century. It may then have spread back into Europe and may have been introduced into other countries for the first time by the import of cattle from North America (Johnson & Kaneene, 1992), resulting in its present worldwide distribution in several countries. The disease is common in Canada, the USA, and South America. There is a low level of infection in Australia and New Zealand. In Europe, the infection or clinical disease remains limited to one or more zones in several countries such as Germany, France, Italy, Greece, and Portugal. Belgium, Czech Republic, Denmark, Germany, Estonia, Spain, France, Ireland, Cyprus, Latvia, Lithuania, Luxembourg, Netherlands, Austria, Slovenia, Slovakia, Finland, Sweden, and United Kingdom are classified as officially EBL-free by the EU (2014/441/UE).

In most of these countries, EBL is a notifiable disease, and official control measures include screening or monitoring, precautions at borders, control of movement inside the country, and stamping out (OIE, 2014). The European legislation aims to eradicate the disease and prevent its spread through trade involving live animals and products. No vaccine is available for BLV.

It is generally thought that BLV is not a hazard to humans; in fact, no conclusive evidence of transmission through the consumption of milk from infected cows has been found (Burmeister et al., 2007, Perzova et al., 2000).

Eradication efforts have been carried out in Italy since 1996 (Ministerial Ordinance n. 358; 02 May 1996). All the Italian regions in which EBL has been eradicated have had to implement a surveillance plan with the aim to identify a novel cluster of infection.

As a consequence of EBL persistence in some Italian regions, on November 2006, the Ministry of Health approved a new legislation (Ministerial Ordinance 14 November 2006) to implement additional eradication measures in the territories of Campania, Calabria, Puglia, and Sicilia.

The objective of this study was to evaluate EBL eradication and surveillance plans in Italy from 2005 to 2012.

Section snippets

Data source

For this study, the results of the EBL eradication or surveillance plans, recorded in the period between 2005 and 2012, were obtained from the Ministry of Health.

The EBL national eradication plan (Ministerial Ordinance 358/1996 and subsequent) states that all bovines, aged more than one year from breeding herds, should be serologically tested twice a year or annually if the herd is considered EBL free. Blood samples were collected by the local veterinary services and submitted to the laboratory

Results

Fig. 1 show the evolution of Italian EBL health status from 2005 to 2012. An overall annual decrease was noted from 0.21% in 2005 to 0.08% in 2012 in the herd prevalence rate, and from 0.027% in 2005 to 0.015% in 2012 in the animal prevalence rate; from 0.06% in 2005 to 0.04% in 2012 in the herd incidence rate (Fig. 2). The outbreaks recorded (from 1 January 2006 to 31 December 2012) in the Veterinary Information System (SIMAN) on 7 November 2013 were 123. Of these, 101 outbreaks occurred in

Discussion

We analysed the eradication measures and surveillance interventions applied for EBL outbreaks in Italy over a period of eight years. The decrease in herd seroprevalence and the stable incidence rates during 2006–2011, except in 2012 when the herd incidence rate decreased, show that the eradication measures had been successful, albeit too slowly.

Implementation of the eradication programme is particularly difficult in the areas of Lazio, Puglia, and Sicilia, where free-range breeding is very

Conclusions

In conclusion, this report shows continuing improvement in the Italian epidemiological situation with regard to EBL. A system built on eradication and national standardised procedures has led to a decrease in infection over time. However, because of the lack of prioritisation of EBL control measures and the scarcity of resources, EBL eradication in all Italians regions is not easily achievable. An inconsistency across surveillance systems implemented in the regions where the disease has been

References (19)

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