Within herd transmission and evaluation of the performance of clinical and serological diagnosis of foot-and-mouth disease in partially immune cattle herds.

The control of foot-and-mouth disease (FMD) in vaccinated populations relies upon surveillance activities such as clinical inspections (CI) and serological monitoring. New evidence to refine current surveillance guidelines has been provided by evaluating (1) the diagnostic performance of CI and serological tests for detection of FMD virus (FMDV) non-structural proteins (NSP), and (2) the within-herd transmission of the virus in partially immune cattle. Data came from 23 affected herds during an epidemic of FMDV type O in Bolivia, in 2007. All cattle (n=957) in these herds were clinically inspected and serum samples were collected one month after the last animal with clinical signs was detected. Samples were tested for the presence of antibodies against NSP using the PANAFTOSA 3ABC-ELISA test and a subset of samples were tested using the enzyme-linked immunoelectrotransfer blot assay (EITB). Data from clinical and serological diagnoses were analysed using a Bayesian model. The sensitivity Se and specificity Sp of the tests, as well as the prevalence and the within-herd reproduction ratio R of FMDV were estimated. In addition, risk factors for infection were identified. The Se of CI, the 3ABC-ELISA and the EITB tests were estimated to be 0.30, 0.88 and 0.96 respectively. The estimated Sp, in the same order, were 0.88, 0.93 and 0.97. The within-herd prevalence of infected animals ranged from 0.04 to 0.91 and R ranged from 1.02 to 2.68. It was observed that cattle coming from areas with high vaccination coverage had a lower risk of becoming infected than home-bred cattle from the affected herds, where vaccination coverage was thought to be low. Although these estimates come from herds kept under specific conditions, they provide a reference for future surveillance design and can inform simulation models for surveillance and control of FMD in similar cattle populations.

Phylogenetic comparison and molecular epidemiology of classical swine fever virus.

The genetic diversity of classical swine fever virus (CSFV) was studied by RT-PCR amplification and sequencing of a 409 bp fragment of the NS5B polymerase region. A total of 106 viruses isolated from 20 countries over a period of 52 years (1945-1997) were included in the phylogenetic study. The results showed that the viruses could be divided into two main groups. Group 1 consisted of Asian and South American isolates from the 1980s, as well as of old European and American isolates. Group 2 consisted mostly of recent European viruses from the 1980s and 1990s, and was further divided into three subgroups largely according to geographic origin and/or year of isolation. Five 1997 CSFV isolates from Germany, Netherlands and Italy clustered together indicating a common origin for these outbreaks, but two other 1997 isolations in different regions of Germany are likely due to different epidemiological events. The results show that the NSSB region of the genome gives a good resolution for phylogenetic studies of CSFV. Molecular epidemiology based on nucleotide sequence diversity is a useful tool for tracing virus spread and for developing disease control strategies.