Day-to-day fluctuation of schistosome circulating antigen levels in serum and urine of humans infected with Schistosoma mansoni in Burundi.

Abstract

Day-today fluctuations of both circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) in serum and urine were examined simultaneously in a group of Schistosoma mansoni-infected individuals from Burundi and compared with each other and with fecal egg count fluctuations. Significant correlations were found between fecal egg counts and circulating antigens (CAA and CCA) and between circulating antigen levels in serum and urine samples. The cumulative percentage of positive results after three samplings was highest for urine CCA detection, followed by fecal egg counts, serum CCA, serum CAA, and urine CAA detection, respectively. It was demonstrated that circulating antigen levels in both serum and urine showed less fluctuation than fecal egg counts, except for urine CAA levels. The serum CAA detection assay in particular, although less sensitive in this low endemic area in Burundi, gave very constant measurements over a period of one week. Our results indicate that detection of circulating antigens in a single serum or urine sample provides a quantitatively more stable diagnosis of S. mansoni infection than fecal egg counts based on a single stool examination.

Practical and ethical issues in the development of a vaccine against schistosomiasis mansoni.

“…If vaccines demonstrate anti-fecundity effects that decrease egg output, infection intensity may have to be determined by circulating antigen concentrations. [52][53][54][55] With respect to the duration of immunity, mathematical models support the concept of vaccine immunity lasting at least five years to be relevant to community health. 34 With those caveats, we propose that a schistosomal vaccine should protect people for at least five years and limit their infection intensity to less than 25 eggs per gram of feces.…”

“…34 All vaccine recipients from disease-endemic areas will therefore have to be prescreened or mass treated. Because of the relative insensitivity of current methods to estimate worm burdens, either by stool egg counts or circulating antigen assays, [52][53][54][55] it is inevitable that some people with undetected or undetectable infections will be immunized. The potential adverse reactions from such an occurrence are currently unknown and should be evaluated, to the degree feasible, in animal models before field clinical trials are initiated.…”

“…59 Egg excretion is also impaired in immunocompromised persons 60,61 and may be decreased by anti-fecundity effects of either naturally acquired resistance or immunization. 62,63 Methods to detect circulating worm or egg antigens in serum, urine, and saliva have shown promise, [53][54][55] and have even been used to evaluate experimental irradiated cercarial immunization where high numbers of challenge cercariae are used. 52 However, these methods likely do not currently possess the requisite sensitivity and specificity to quantitate worm burdens in vaccine clinical trials, especially when these are low.…”

“…84,85 The current insensitivity of methods to detect developing and adult worms as well as incipient immunopathology would also constrain the requisite close monitoring of these volunteers. [52][53][54][55] It is therefore not planned that volunteer protection studies will be used to further schistosomal vaccine development.…”

Age-related worm load and worm fecundity patterns in human populations, as indicated by schistosome circulating antigens

“…CAA is a glycoconjugate associated with the gut of the adult worm and released by the parasite in large amounts into the circulation of the infected host. CAA detection in serum appears to give a quantitatively stable diagnosis of S. mansoni infection (Polman et al 1998). Several animal studies have shown a good correlation between worm loads and CAA levels (Deelder et al 1994, Agnew et al 1995.…”