Using ultrasonography, this survey provides normal, standard organometric data for a Cameroonian population that can be used as the basis for assessing hepatic morbidity in neighbouring S. mansoni endemic areas or in other countries with comparable settings (other S. mansoni endemic areas either in Cameroon or in the Central Africa). To achieve this objective, with a sample representative of the endemic area, school children were enrolled from 5 neighbouring villages with different S. mansoni prevalences.
Prior to selection and inclusion as healthy controls for the establishment of liver parameters normal ranges, participants were screened for S. mansoni and/or other geohelminths eggs by the Kato katz technique and only negative cases were retained. However, considering the known low sensitivity of this technique to detect S. mansoni and other geohelminths eggs21,22, the likelihood of false negative cases for low-burden infections persisted. To render our parasitological screening a bit more robust, 2 stool samples were collected from each participant at 2 different days and examined by 2 different and experienced technicians, as this was reported to improve the Kato-Katz the sensitivity23,24,25. Furthermore, ultrasonographic data (n = 556) were obtained from Kato katz negative-participant and those showing a Liver Image Pattern (LIP) A i.e. with no abnormalities were included for downstream analyses, consistent with the global approval of this pattern as the only pattern of no liver disease in schistosomiasis-affected areas1,5,26,27. Of note, LIP B, considered as representative of liver disease by some authors26,27 or as borderline by orders3,5,11, was also excluded from our study to strictly include participants with no signs of possible liver disease. This caution was additionally taken to further exclude potential kato katz false negative-participants with nascent liver lesions. Moreover, all participants positives for malaria, hepatitis B or hepatitis C were also excluded since all those pathogens develop through a stage within the liver28,29, and could possibly lead to abnormal liver organometric parameters30,31,32. This approach had the merit of adding stringency in selecting healthy subjects in our present study when compared to previous studies16,17,18,19,20 that have defined regional liver organometric referential in schistosomiasis-endemic areas.
Normal ranges of liver lobe sizes increased with participant height. For instance, in the [100–120 cm] height group, the current reference value of length of the left liver lobe is below 94.8 mm (mean ± 2 S.D.). A size above 94.8 mm is therefore regarded as abnormal considering the traditional cut-off values. Within the (>160 cm) height group, the mean left liver lobe size was 101 mm and a participant with a left liver size of 120 mm is considered as normal. This further confirm the variation of the liver organometry with the body height. Consequently, to avoid misinterpretation and then improve the diagnosis accuracy, our study confirms that, in ultrasound-based hepatic morbidity monitoring studies, each participant should be compared with the standard range of his height group. Our report provides such a standard set of normal ranges of liver organometry adjusted for body height for a population group from Bokito in rural Cameroon.
It should be noted, however, that in as much as we included a variety of sites of the rural locality of Bokito within the Centre region of Cameroon, there is no definitive representation of the entire ecological regions of Cameroon in our sampled study population. The particularity of the study, however, is that school children from Cameroon, a hitherto non-used population pool in African and world schistosomiasis endemic area are now used to define a liver organometry referential. This should be of relatively higher accuracy for studies in the country than foreign referentials. In fact, the absence of any such referential in the central African region proposes the presently defined referential as the closest to reality that investigators and national control programs could use to more reliably assess morbidity in the region.
Comparative analyses of available ultrasound-based liver organometric referentials supports such a claim. When compared to the available referential in Northern Senegal16, except for the left liver lobe size, all other liver parameters were higher in participants from Senegal when compared to our Cameroonian cohort. For instance, within the height group (141–160); the right liver love (140.0 vs 126.9); the portal vein thickness (5.0 vs 2.3) and the main portal vein diameter (10.8 vs 9.6) were higher in participants from Senegal compared to our study participants. However, the left liver lobe (84.0 vs 94.1) was smaller in participants from Senegal16, though we have to consider that the later study was conducted within the whole population including adult (age range from 4 to more than 40 years) in an area not endemic for schistosomiasis unlike ours. Compared to the referential established in China (age range 4–33 years)19, all liver parameters were rather higher in participants from our study population. Within the same height group (141–160), participants from China showed a smaller left liver lobe (63.4 vs 94.1), right liver lobe (111.6 vs 126.9), portal vein thickness (2.2 vs 2.3) and main portal vein diameter (8.6 vs 9.6) compared to our study participants19. These observations could be possibly explained by the geographical, nutritional and biometric difference across geographically distinct populations11, further confirming the need to establish normal ranges of liver parameters adjusted for body height in as many areas as feasible.
Of note and in contrast to the referential-defining study conducted in Zimbabwe17, we found, in our study population, that males displayed a significant bigger left and right liver lobe compared to females. Even though males are generally taller than females, this argument could not be an explanation here given our calculation approach where males and females parameters where only comparatively considered within a similar height range. Certainly, this observation reemphasizes the physiological impact of the gender on the liver organometrics. In fact, univariate regression models further confirmed these discrepancies. This inter-gender heterogeneity in normal liver organometric values might therefore be as important in introducing misinterpretation in studies as that of the erroneous use of a same referential to compare participants from different endemic regions11. Our results therefore suggest that despite belonging to a same height group, males and females should have different standardised normal ranges (referential curves) to avoid misinterpretations.
Although increased spleen length and thickness have been reported during S. japonicum infection33, spleen organometry was not defined in our cohort since spleen enlargement has not been broadly considered as a parameter to assess morbidity owed to S. mansoni infection19 and consistent with the heavily reported prevalence of malaria, as a spleen-size-altering disease, in the presently studied region of Bokito.
Overall, normal liver organometrics, influenced by biometric factors that reportedly vary across different population and gender groups11,16, is hereby defined from school children in a hepatic schistosomiasis endemic site in the subdivision of Bokito in rural Cameroon. A gender-specific liver organometry referential is therefore provided to ameliorate the precision in the ultrasound-based evaluation of liver pathology in the area, complementing currently available referentials from other endemic areas in assisting monitoring surveys of hepatic schistosomiasis-associated liver morbidity in the region.