Predicting Kala-Azar Disease Manifestations in Asymptomatic Patients with Latent Leishmania donovani Infection by Detection of Antibody against Recombinant K39 Antigen

Clinically visceral leishmaniasis is suspected in only a fraction of infected persons, as the majority of these may not have clinical manifestations and remain asymptomatic. There is scanty information on diagnosing latent infections and predicting disease in asymptomatic persons. We therefore carried out a study on asymptomatic contacts of patients with visceral leishmaniasis and post-kala-azar dermal leishmaniasis by using methods for detection of antibody to recombinant K39 (rK39) antigen. A total of 240 patients with leishmaniasis and 150 asymptomatic contacts were tested for anti-rK39 immunoglobulin G (IgG) and IgA antibodies. Fifty-five asymptomatic persons were found to be seropositive. These individuals were monitored every 3 months for 1 year. On follow-up, 43.9% of the asymptomatic seropositive contacts developed kala-azar within the first 3 months, and a cumulative total of 69% developed kala-azar within 1 year. The rest remained asymptomatic and self-healed the infection. The sensitivity and specificity of rK39 enzyme-linked immunosorbent assay (ELISA) and dipstick tests were 100%, while an in-house-developed latex agglutination test had 80% sensitivity. The antibody profile showed that the IgG anti-rK39 antibodies reached a titer of up to 10(−6) within 6 months of infection, started declining thereafter, and completely disappeared in 2 to 3 years in successfully treated cases. Significant titers of IgA antibodies were detectable a little earlier than those of IgG antibodies and were undetectable after 6 months. The study showed that mass screening of family members and contacts by using anti-rK39 ELISA could be a highly reliable tool for early diagnosis and to plan prophylactic treatment of latently infected asymptomatic carriers to eradicate kala-azar.

仅在部分感染者中可怀疑临床型内脏利什曼病（visceral leishmaniasis），因多数感染者无明显临床表现，呈无症状感染状态。目前针对潜伏感染的诊断及无症状人群的发病预测相关研究资料尚十分匮乏。为此，本研究针对内脏利什曼病患者与黑热病后皮肤利什曼病（post-kala-azar dermal leishmaniasis）患者的无症状密切接触者开展研究，采用检测重组K39（rK39）抗原抗体的方法进行分析。本研究共纳入240例利什曼病患者及150名无症状接触者，对其抗rK39免疫球蛋白G（IgG）与免疫球蛋白A（IgA）抗体进行检测。最终检出55例血清学阳性的无症状个体，随后对该群体开展为期1年、每3个月1次的随访监测。随访结果显示，43.9%的血清学阳性无症状接触者在随访首3个月内进展为黑热病（kala-azar），随访1年时累计已有69%的受试者出现黑热病；其余受试者则维持无症状状态，并实现感染自愈。重组K39酶联免疫吸附试验（ELISA）与试纸条检测的灵敏度及特异度均为100%；本研究所自研的乳胶凝集试验（latex agglutination test）灵敏度则为80%。抗体谱分析结果表明，在成功接受治疗的病例中，感染后6个月内抗rK39 IgG抗体滴度可达10^(-6)，随后开始逐步下降，并在2至3年内完全消失。IgA抗体的可检出时间略早于IgG，且在感染后6个月即无法被检测到。本研究证实，采用抗rK39 ELISA对患者家属及密切接触者开展大规模筛查，可作为黑热病早期诊断的高可靠工具，并可为潜伏感染的无症状携带者制定预防性治疗方案提供依据，助力黑热病的根除工作。