Specific immune responses are required to control parasitemia in Babesia equi infection

Abstract

Horses possessing a normal immune system and spleen often control infection caused by Babesia equi. However, splenectomized horses are unable to control B. equi infection and usually succumb to the infection. To investigate the role of the spleen in the control of B. equi infection in the absence of specific immune responses, two 1-month-old foals with severe combined immunodeficiency (SCID) and two age-matched normal foals were inoculated with B. equi. The SCID foals became febrile seven days postinoculation and developed terminal parasitemias of 41 and 29%. The SCID foals had greater than 50% decreases in indices of total erythrocytes, packed-cell volumes, and hemoglobin concentrations. Both SCID foals were euthanized in extremis at 10 days postinoculation. As expected, the serum of the SCID foals lacked detectable antibodies to B. equi antigens. In contrast, the normal foals inoculated with B. equi produced detectable anti-erythrocytestage parasite antibodies by 7 days and controlled clinical disease by 12 days postinoculation. Although SCID foals lack functional T and B lymphocytes, they do possess complement, macrophages, granulocytes, and natural killer cells, as well as a spleen. Therefore, the data indicate that specific immune responses are required to control B. equi parasitemia but are not required for erythrocyte lysis in infected horses. Furthermore, the spleen is not able to control B. equi parasitemia in the absence of specific immune responses to parasite antigens.

Review of Equine Piroplasmosis

“…Although innate immunity is unaffected, SCID foals lack functional T and B lymphocytes and are incapable of mounting antigenspecific antibody and cellular immune responses. [85][86][87][88][89][90][91] Inoculation of these foals with T. equi resulted in fulminant, severe infection within 7 days, and subsequent death. Terminal parasitemias ranged between 29 and 41% and PCV decreased by 50% of the normal value.…”

“…92 T. equi-infected horses produce antibodies against immunodominant merozoite proteins termed equi merozoite antigens (EMAs), which are surface expressed on merozoites. 85 The exact role of this antibody response in immunity and persistence remains unclear. The nomenclature of equine immunoglobulin G has recently been adjusted to accommodate the 7 unique IgG heavy chain genes discovered in the equine genome.…”

Equine piroplasmosis: An updated review

“…But these foals have an intact spleen and competent innate immune system. This demonstrates that the spleen is unable to control T. equi infection in the absence of adaptative parasite-specific immune response (McGuire et al 1975;Knowles et al 1994;Wiler et al 1995;Shin et al 1997). Equine piroplasmosis infection produces a strong humoural response.…”

Determinação da infecção por Theileria equi e Babesia caballi em equinos alojados no Jóquei Clube de São Paulo por meio da técnica de C-ELISA (Competitive Enzyme Lynked Immunosorbent Assay)

“…essa queixa antecedeu o quadro clínico de babesiose sendo que o quadro de queda de desempenho nem sempre é identificado como um problema que deve ser corretamente diagnosticado e tratado. Na prática corrente do meio equestre, via de regra, os animais são submetidos a tratamentos com drogas babesicidas a qualquer sinal de queda de desempenho, mesmo que o diagnostico final não tenha sido realizado.Os animais imunocompetentes e que sobrevivem à infecção aguda tornam-se portadores assintomáticos e serão carreadores da babesiose(RONCATI, 2006).Esses animais estarão protegidos da doença severa em função da produção de anticorpos por parte do sistema imune que está continuamente sendo estimulado pelos parasitas remanescentes(KNOWLES et al, 1994).Animais infectados por Theileria equi persistem infectados por anos, provavelmente durante toda vida, enquanto que infecções por Babesia caballi não são persistentes e são pouco estáveis. A doença torna-se crônica devido à fraca imunidade natural do hospedeiro que se deve à adaptação do parasito às defesas naturais, ou seja, sua capacidade de evasão da resposta imune através da variação de seus antígenos de superfícies(NIZOLI, 2005).…”

“…causada pela babesiose. A ação concomitante da resposta de anticorpos e do baço foi estudada porKnowles et al, 1994. quando utilizaram potros SCID (Severe Combinated Imunodeficiency) e animais esplenectomizados para avaliar as respostas imunes na patogênese e controle da doença causada por Theileria equi.…”