Resolution of a classical swine fever outbreak in the United States-Mexico border region.

On 11 August 1999, an outbreak of classical swine fever (CSF) occurred in the municipality of San Carlos in the State of Tamaulipas, located on the United States-Mexico border. Sixty-eight dead and two sick pigs from a village were reported to the animal health authorities; tissue samples of sick pigs were confirmed as positive for CSF virus by indirect fluorescent antibody test. The population at risk consisted of 521 pigs, with crude mortality and attack rates of 13.05% and 0.38% respectively. However, on 24 August 1999, two more pigs were detected with clinical signs and their tissue samples confirmed as positive by indirect fluorescent antibody test and neutralizing peroxidase-linked assay, with a secondary attack rate of 0.38%. The outbreak was eradicated by implementing a slaughter policy, movement control, quarantine and surveillance, among other measures. After 6 months of quarantine, the disease was eradicated without resorting to vaccination. The possible sources of introduction of the CSF are also discussed.

Situation of classical swine fever and the epidemiologic and ecologic aspects affecting its distribution in the American continent.

Classical swine fever (CSF) is a viral transboundary animal disease that is highly contagious among domestic and wild pigs, such as boars and peccaries. Today, far from being what was classically described historically, the disease is characterized as having a varied clinical picture, and its diagnosis depends on resorting to proper sample collection and prompt dispatch to a laboratory that can employ several techniques to obtain a definitive diagnosis. Laboratory findings should be complemented with a field analysis of the occurrence of disease to have a better understanding of its epidemiology. The disease is still present in various regions and countries of Latin America and the Caribbean, thus hindering production, trade, and the livestock economy in the region. Consequently, it is among the diseases included in List A of the Office International des Epizooties (OIE). Currently, there are epidemiologic and ecologic aspects that characterize its geographical distribution in the region such as: continued trends in the demand for pork and pork products; an increase in swine investment with low production costs which are able to compete advantageously in international markets; the convention of associating CSF in the syndrome of "swine hemorrhagic diseases" owing to the historical description of its acute presentation and not to the new and more frequent subacute presentations or the diseases with which it may be confused (notably, porcine reproductive and respiratory syndrome and porcine dermopathic nephropathy syndrome, among others); dissemination of the virus through asymptomatic hosts such as piglets infected in utero; frequent lack of quality control and registration of vaccines and vaccinations; feeding of swine with contaminated food waste (swill); the common practice of smuggling animals and by-products across borders; the backyard family production system or extensive open field methods of swine rearing with minimal input in care and feeding; poor understanding of the epidemiologic role that boars and peccaries could have in the transmission and maintenance of the disease in the Americas; and new procedures in animal welfare that some countries are adopting for the production, transport, and slaughter of domestic animals. Consequently, many countries (i.e., Canada, USA, Chile, Belize, Costa Rica, Panama, and Mexico, where 13 of 32 States are disease free) have given priority to the control and progressive eradication of CSF. In other parts of the Americas, the disease appears under control, as is the case of the five countries of the Andean Region and the 12 northern States of Brazil. In South America, Chile, Uruguay and 13 States in Brazil are disease free. Argentina has mounted a national campaign and is in the process of eradicating the disease. No recent information on its presence or distribution in Paraguay is available. With no master strategy to harmoniously progress in the control and eradication of the disease, 17 countries of the region, jointly led by the Food and Agriculture Organization of the United Nations, developed the Continental Plan for the Eradication of CSF whose objective is expected to be reached by 2020.

The effect of vaccination with the PAV-250 strain classical swine fever (CSF) virus on the airborne transmission of CSF virus.

The airborne transmission of Classical Swine Fever (CSF) virus to susceptible pigs, as well as the effect of vaccination with the CSF virus PAV-250 strain was investigated on this mode of transmission. Experiment I: four pigs were inoculated with the ALD CSFV strain (10(4.3) 50% TCID) by the intramuscular route, and at the onset of fever, they were introduced into an enclosed chamber. At the end of the experiment surviving pigs were sedated, anesthetized and euthanatized. Experiment II: four pigs were previously vaccinated with the CSF virus PAV-250 strain, and at 14 days post-vaccination they were challenged with the CSF virus ALD strain. In both experiments, four susceptible pigs were exposed to infectious aerosols by placing them in a chamber connected by a duct to the adjacent pen containing the infected animals and were kept there for 86 hs. In Experiment I, pigs exposed to contaminated air died as a result of infection with CSF virus on days 14, 21 and 28 post-inhalation. These four pigs seroconverted from day 12 post-inhalation. CSF virus was isolated from these animals, and the fluorescent antibody test on tonsils was positive. In Experiment II, a vaccinated pig exposed to contaminated air did not seroconvert, nor was CSF virus isolated from lymphoid tissues. However, mild fluorescence in tonsil sections from these pigs was observed. In conclusion, CSF virus was shown to be transmitted by air at a distance of 1 m to susceptible pigs. Vaccination with the PAV-250 CSF virus strain protected the pigs from clinical disease under the same conditions.