Amoebiasis: antibodies to Entamoeba histolytica in the blood
Last reviewed: 23.04.2024
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Antibodies to Entamoeba hystolitica in serum are not normally present.
The causative agent of amebiasis is Entamoeba hystolitica, exists in three forms: tissue ( forma magna ), luminal ( forma minuta ) and cystic ( forma cystica ). The disease is met everywhere. In many regions, healthy carriers account for 14-20% of the total population. The diagnosis of intestinal amebiasis is established based on the detection of the pathogen in feces or tissues (examine the biopsy) using special dyes. In the feces, Entamoeba hystolitica antigens (adhesin) can be detected by ELISA. The diagnostic sensitivity of ELISA for the detection of Entamoeba hystolitica adhesin in feces is 96.9-100%, specificity is 94.7-100%. In some cases, the diagnosis of extraintestinal amebiasis is difficult, since the test systems for detecting Entamoeba hystolitica antigens can give false positive results. Often, they are caused by the presence of other intestinal pathogens ( Ascaris lumbricoides, Blastocystis hominis, Clostridium difficile, Cryptosporidium, Enmatoeba coli, Salmonella typhimurium, Shigella zonnei, etc.). To resolve such cases, the level of specific antibodies in serum is examined.
The most sensitive of serological methods are RPHA (sensitivity and specificity at a titer of more than 1: 128 - about 95%), RIF and ELISA (reveals antibodies IgM and IgG, more sensitive and specific). Antibodies to Entamoeba hystolitica in serum using RPHA are detected in almost all patients with amebic liver abscess (AST and ALT are increased 2-6 times, alkaline phosphatase 2-3 times) and in most individuals with acute amebic dysentery. The increase in the titer of antibodies in the study of paired sera after 10-14 days by no less than 4 times or at a single study of the titer above 1: 128 is considered to be diagnostic. Antibodies usually do not reveal in asymptomatic cysts (only in 9% of cases), which indicates that the synthesis of antibodies requires the introduction of an agent in the tissue, and in patients with immunosuppression. Elevated antibody titers can persist for several months or years after complete recovery.
Specific antibodies in the RIF with amoebic antigen are detected in 98-100% of cases of clinically expressed amebic liver abscess, RIF gives a positive result in 75-80% of patients with invasive amoebiasis of the intestine, especially with fulminant colitis, amoeboma and peritonitis. When interpreting the results of the RIF, it should be taken into account that the antibody titer of 1: 320 and above indicates, as a rule, a clinically pronounced, often extra-intestinal form of amoebiasis. In the titer of 1: 80-1: 160, antibodies are found in patients with amoebiasis at the time of examination or recovered in the recent past, as well as in the case of slow, erased forms of intestinal amoebiasis. The titer of antibodies 1:40 can be detected in persons with symptoms of intestinal amebiasis, with a corresponding epidemic history and unresolved status of the patient. In this case, the study of paired sera is effective. The elevation of the antibody titer after treatment is evidence in favor of the amoebic etiology of the process. False positive result in the titer of 1:40 can be registered in patients with systemic and oncological diseases. Low antibody titer (1: 20-1: 40) is often found among asymptomatic carriers of the causative agent of amebiasis. A consistent steady decline in antibodies that have recovered from titer is below 1:20 - the indicator of treatment effectiveness, the rise of titers and the appearance of clinical symptoms should be regarded as a relapse of the disease.
Antibodies IgM to Entamoeba hystolitica in serum using ELISA are detected in almost all patients with amebic liver abscess (more than 90%) and in the majority of persons with acute amebic dysentery (in 84% of cases). They disappear within 6 weeks after effective treatment. IgG antibodies are detected at about the same frequency as IgM, they indicate the current (with increasing antibody titer) or previously transmitted (if the antibody content does not change) infection. In the presence of symptoms of diarrhea, serological tests are usually positive in more than 90% of patients, in their absence - less than 50%.
The determination of antibodies to Entamoeba hystolitica is used to diagnose amoebiasis infection (amoebic dysentery), to monitor the dynamics of the disease and the consequences of infection.
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