For some time it has been known that the tick Ornithodoros erraticus might be one of the causes of the persistence of African swine fever in the Iberian Peninsula since its introduction in 1960. In the province of Salamanca serological methods have been used to study the relationship between the presence of the tick in different townships and the outbreaks of African swine fever in these townships between 1987 and 1992. The results showed that there was a statistically significant association between the presence of the parasite and the persistence of African swine fever. In townships without O erraticus traditional methods of control are in most cases enough to avoid new outbreaks of the disease, but in areas with O erraticus the traditional methods should be reinforced by other methods for preventing contact between pigs and the parasite.

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We analysed in mice why the salivary gland extract (SGE-2) from Ornithodoros erraticus and O. moubata induce a protective response with Freund's adjuvants (FAs) in swine while the saliva, in natural conditions, does not. Such protection has been ascribed to the fact that administration of SGE-2 plus FAs permits the recognition of certain salivary components that under natural conditions are not immunogenic. The present findings confirm this hypothesis since in mice, which are unable to recognize the above components, the SGE-2-FAs do not induce any protection. We rule out the possibility that the cause of this could lie in the absence of prostaglandin E2 in the SGE-2 (vs saliva) since it is not present in either fluid. Neither could it be due to a change in antibody isotype since those induced by parasites bites and by the SGE-2-FAs are the same (IgG2a > IgG1 > IgG2b; not IgG3, IgM, IgE). No IgG2a were seen when the SGE-2 were administered alone or with alum or ricin. It is therefore suggested that first responses would be Th1 and the second ones Th2, although no IgE is seen in the latter responses either. The parasites do not require complement to feed; by contrast, they block its activation and skin cellular infiltrates, such as those elicited by IL-8, MCP-1 and C5a, do not affect them, regardless of the presence or not of antitick antibodies.