Hyalomma anatolicum anatolicum: the role of humoral factors in the acquisition of host resistance

The control of Hyalomma ticks, vectors of the Crimean–Congo hemorrhagic fever virus: Where are we now and where are we going?

At a time of major global, societal, and environmental changes, the shifting distribution of pathogen vectors represents a real danger in certain regions of the world as generating opportunities for emergency. For example, the recent arrival of the Hyalomma marginatum ticks in southern France and the concurrent appearance of cases of Crimean–Congo hemorrhagic fever (CCHF)—a disease vectored by this tick species—in neighboring Spain raises many concerns about the associated risks for the European continent. This context has created an urgent need for effective methods for control, surveillance, and risk assessment for ticks and tick-borne diseases with a particular concern regarding Hyalomma sp. Here, we then review the current body of knowledge on different methods of tick control—including chemical, biological, genetical, immunological, and ecological methods—and the latest developments in the field, with a focus on those that have been tested against ticks from the genus Hyalomma. In the absence of a fully and unique efficient approach, we demonstrated that integrated pest management combining several approaches adapted to the local context and species is currently the best strategy for tick control together with a rational use of acaricide. Continued efforts are needed to develop and implement new and innovative methods of tick control.

Disease-bearing Hyalomma ticks are an increasingly emerging threat to humans and livestock worldwide. Various chemical, biological, genetic, and ecological methods for tick control have been developed, with variable efficiencies. Today, the best tick control strategy involves an integrated pest management approach.

Immunobiology of Acquired Resistance to Ticks

Ticks are blood-sucking arthropods of great importance in the medical and veterinary fields worldwide. They are considered second only to mosquitos as vectors of pathogenic microorganisms that can cause serious infectious disorders, such as Lyme borreliosis and tick-borne encephalitis. Hard (Ixodid) ticks feed on host animals for several days and inject saliva together with pathogens to hosts during blood feeding. Some animal species can acquire resistance to blood-feeding by ticks after a single or repeated tick infestation, resulting in decreased weights and numbers of engorged ticks or the death of ticks in subsequent infestations. Importantly, this acquired tick resistance (ATR) can reduce the risk of pathogen transmission from pathogen-infected ticks to hosts. This is the basis for the development of tick antigen-targeted vaccines to forestall tick infestation and tick-borne diseases. Accumulation of basophils is detected in the tick re-infested skin lesion of animals showing ATR, and the ablation of basophils abolishes ATR in mice and guinea pigs, illustrating the critical role for basophils in the expression of ATR. In this review article, we provide a comprehensive overview of recent advances in our understanding of the cellular and molecular mechanisms responsible for the development and manifestation of ATR, with a particular focus on the role of basophils.

Boophilus microplus: the pattern of bovine immunoglobulin isotype responses to high and low tick infestations

Cattle present variable levels of resistance to ticks and the immune correlates of these heritable phenotypes must be known in order to develop effective vaccines. The antibody responses to tick salivary antigens were examined in cattle of tick-susceptible (Holstein) and tick-resistant (Nelore) breeds. After heavy infestations, levels of IgG1 and IgG2 antibodies decreased in Holsteins and remained the same in Nelores. Conversely, levels of IgE antibodies increased in Holsteins. Different sizes of tick burdens modulated the IgG1 antibody response in a susceptible breed (Aberdeen): levels were higher than in controls in heavily infested animals, but not in those undergoing intermediary or minimal infestations. The three experimental groups presented similar levels of IgG2 antibodies. Levels of IgE antibodies were higher only in animals undergoing intermediate infestations. These results indicate that tick infestations suppress the IgG antibody response in susceptible breeds, that IgE antibodies are not protective, and that the dose of tick saliva modulates the isotype of host antibody responses.

Immunological response in rabbits infested with Rhipicephalus sanguineus

In order to clarify the importance of humoral antibody in host resistance to ticks, in the present work we studied the immunological response of rabbits infested with larvae, nymphs or adults of Rhipicephalus sanguineus, using extracts of eggs (EE), larvae (LE), nymphs (NE), male salivary glands (MSGE), male midguts (MME), female salivary glands (FSGE) and female midguts (FME). When serum from rabbits infested with larvae or nymphs was tested using enzyme-linked immunosorbent assay, no reactions were observed with any of the extracts including the homologous LE or NE. In sera from rabbits infested with adult ticks, the reactions were observed in both homologous (MSGE, MME, FSGE and FME) and heterologous (EE, LE and NE) system. However, differences were seen regarding the type of antigen used. When the experiment was carried out using extracts from adults higher responses were found. With FSGE and FME antigens, antibody levels were systematically higher than those observed when MSGE and MME were used.