Amoebiasis: antibodies to Entamoeba histolytica in blood

Antibodies to Entamoeba hystolitica are normally absent in blood serum.

The causative agent of amebiasis is Entamoeba hystolitica, which exists in three forms: tissue ( forma magna ), luminal ( forma minuta ) and cystic ( forma cystica ). The disease is found everywhere. In many areas, healthy carriers make up 14-20% of the entire population. The diagnosis of intestinal amebiasis is established based on the detection of the pathogen in feces or tissues (biopsy is examined) using special dyes. In feces, Entamoeba hystolitica antigens (adhesin) can be detected by ELISA. The diagnostic sensitivity of ELISA for detecting 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 test systems for detecting Entamoeba hystolitica antigens can give false-positive results. They are often caused by the presence of other intestinal pathogens ( Ascaris lumbricoides, Blastocystis hominis, Clostridium difficile, Cryptosporidium, Еntamoeba coli, Salmonella typhimurium, Shigella zonnei etc.). To resolve such cases, the level of specific antibodies in the blood serum is examined.

The most sensitive of the serological methods are RPGA (sensitivity and specificity at a titer of more than 1:128 - about 95%), RIF and ELISA (detects IgM and IgG antibodies, more sensitive and specific). Antibodies to Entamoeba hystolitica in the serum using RPGA are detected in almost all patients with amoebic liver abscess (AST and ALT are increased by 2-6 times, alkaline phosphatase - by 2-3 times) and in most people with acute amoebic dysentery. An increase in the antibody titer in the study of paired sera after 10-14 days by at least 4 times or in a single study a titer higher than 1:128 is considered diagnostic. Antibodies are usually not detected in asymptomatic cyst excretors (only in 9% of cases), which indicates that the introduction of the pathogen into tissues is necessary for the synthesis of antibodies, and in patients with immunosuppression. An increased antibody titer can persist for several months or years after complete recovery.

Specific antibodies in RIF with amoebic antigen are detected in 98-100% of cases of clinically expressed amoebic liver abscess, RIF gives a positive result in 75-80% of patients with invasive intestinal amebiasis, especially with fulminant colitis, ameboma and peritonitis. When interpreting RIF results, it should be taken into account that an antibody titer of 1:320 and higher usually indicates a clinically expressed, more often extraintestinal form of amebiasis. In a titer of 1:80-1:160, antibodies are detected in patients with amebiasis at the time of examination or who have had the disease in the recent past, as well as in the case of sluggish, latent forms of intestinal amebiasis. An antibody titer of 1:40 can be detected in individuals with symptoms of intestinal amebiasis with a corresponding epidemiological history and an uncomplicated patient status. In this case, a study of paired sera is effective. An increase in the antibody titer after treatment indicates an amoebic etiology of the process. A false positive result in a titer of 1:40 can be registered in patients with systemic and oncological diseases. A low antibody titer (1:20-1:40) is often found among asymptomatic carriers of the causative agent of amebiasis. A consistent, steady decrease in the antibody titer below 1:20 in those who have recovered is an indicator of the effectiveness of treatment; an increase in titers and the appearance of clinical symptoms should be regarded as a relapse of the disease.

IgM antibodies to Entamoeba hystolitica in serum using ELISA are detected in almost all patients with amoebic liver abscess (more than 90%) and in most individuals with acute amoebic dysentery (in 84% of cases). They disappear within 6 weeks after effective treatment. IgG antibodies are detected with approximately the same frequency as IgM, they indicate a current (with an increase in the antibody titer) or a previous (if the antibody content does not change) infection. In the presence of diarrhea symptoms, serological tests are usually positive in more than 90% of patients, in their absence - in less than 50%.

Determination of antibodies to Entamoeba hystolitica is used to diagnose amoebic infection (amoebic dysentery), monitor the dynamics of the disease and the consequences of the infection.

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