An extensive ultrasound and serologic study to investigate the prevalence of human cystic echinococcosis in northern Libya

A prevalence study of abdominal cystic echinococcosis (CE) was undertaken in the northwest, northcentral, and northeast regions of Libya. A total of 36 villages along the coast were included, in which 20,220 people were screened by portable ultrasound. Three hundred thirty-nine (1.7%) were diagnosed with CE. There was no significant difference between CE prevalence rates in the three regions of Libya (mean = 1.6%); however, intervillage rates were variable, ranging from 0% to 4.5%. The prevalence of CE increased significantly with age (P < 0.0001) and females were significantly more affected (2%) than males (1.3%) (P < 0.0001). Cases of CE were distributed among 3.2% of housewives, 2.6% of farmers, 2.3% of male civil servants, 1.3% of female students, and 1.1% of male students. Housewives (P < 0.0001) and students (P < 0.0001) were significantly more at risk for CE. A statistically significant proportion (62% [210 of 339]) of CE cases kept dogs (P < 0.0001). Of the ultrasound-positive CE cases 69% (233 of 339) were antibody seropositive by ELISA using Echinococcus granulosus hydatid cyst fluid antigen B. Blood samples (n = 10,096) collected onto filter papers were taken randomly from ultrasound-negative people who entered the study, of which 11.2% were found to be seropositive. Seropositivity increased with age (P < 0.0001), with females exhibiting higher seroprevalence than males for all age groups (P < 0.0001). Seroprevalence was distributed occupationally among 17.3% of female students, 11.2% of male students, 8.3% of housewives, 7.3% of farmers, and 6.4% of male civil servants. Housewives and students were more likely to be seropositive (P < 0.0001). Forty-seven percent (526) of the seroreactors kept dogs. All liver hydatid cysts detected by ultrasound during community screening were classified according to morphology and size into six types. Type I (17.5% of all cases) were small univesicular cysts less than 50 mm in diameter with no laminations or daughter cysts. Type II (34%) were univesicular cysts with only laminations. Type IIIa (8.5%) were univesicular cysts with the appearance of laminations and daughter cysts. Type IIIb (13%) were univesicular with laminations and less prominent daughter cysts. Type IV (5.6%) presented as a solid mass. Type V were degenerated calcified or partially calcified cysts (13.2%). Type VI presented as multiple cysts (8% of all cases). The CE cases that exhibited Types II, IIIa, IIIb, IV or VI cysts showed the highest seropositivity (86%, 96%, 95%, 100%, and 96%, respectively), while Types I and V were the least seroreactive (38% and 22%, respectively). Cases of CE occurred in 311 families, with 93% having only one member as a CE case while 7% of the families had two or more cases. However, 25% of the ultrasound-negative persons belonging to families with an index CE case were seropositive for antibodies to Echinococcus. These results confirm the importance of human CE in Libya. They also confirm the usefulness of ultrasound combined with serology as a mass screening approach for CE in north African communities.