Abstract
Ticks are second to mosquitoes as vectors of disease. Ticks affect livestock industries in Asia, Africa and Australia at ~ $1.13 billion USD per annum. For instance, 80% of the global cattle population is at risk of infestation by the Rhipicephalus microplus species-complex, which in 2016 was estimated to cause $22–30 billion USD annual losses. Although the management of tick populations mainly relies on the application of acaricides, this raises concerns due to tick resistance and accumulation of chemical residues in milk, meat, and the environment. To counteract acaricide-resistant tick populations, immunological tick control is regarded among the most promising sustainable strategies. Indeed, immense efforts have been devoted toward identifying tick vaccine antigens. Until now, Bm86-based vaccines have been the most effective under field conditions, but they have shown mixed success worldwide. Currently, of the two Bm86 vaccines commercialized in the 1990s (GavacTM in Cuba and TickGARDPLUS™ in Australia), only Gavac™ is available. There is thus growing consensus that combining antigens could broaden the protection range and enhance the efficacies of tick vaccines. Yet, the anticipated outcomes have not been achieved under field conditions. Therefore, this review demystifies the potential limitations and proposes ways of sustaining enhanced cocktail tick vaccine efficacy.
Highlights
Ticks are obligate blood-feeding parasites that are capable of transmitting pathogens both to humans and animals [1,2]
Argasid tick species of the genus Ornithodorus transmit the African swine fever virus, which causes a fatal haemorrhagic fever disease in pigs that leads to 100% mortality which severely affects the pig-industry of sub-Saharan Africa, Asia, eastern Europe [11]
Ndawula et al [45] demonstrated that serum independently induced against the recombinant glutathione S-transferase cross-reacts against heterologous tick species rGSTs, at varying intensities
Summary
Ticks are obligate blood-feeding parasites that are capable of transmitting pathogens both to humans and animals [1,2]. It is presumed that when ingested during blood feeding, the anti-tick antigen sera could interfere with the physiological functionality of internal tick proteins Building on these observations, numerous recombinant tick antigens have been identified against Ixodid ticks [18,19,20,21], of which Bm86 is still the most successful under field conditions [34,35]. Trager [28] and several other research groups [22] have demonstrated that Agarsid tick-extracts can induce acquired immunity in vivo, the progress toward the development of subunit vaccines against Argasids has been slow. Likely that ticks express a plethora of proteins depending on their environment This further supports the hypothesis that the provision of cocktail vaccine antigens could enhance anti-tick protection efficacy [25]
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