Of ants and men (an antology).

Figure 2. A hatching Dicrocoelium dendriticum miracidium from the patient's stool sample (original magnification, ϫ20). Figure 1. A Dicrocoelium dendriticum egg. The dark brownish egg is thick-walled and relatively small when compared with other helminthic eggs found in human feces (size, 40 mm ϫ 20 mm). A not-very-prominent operculum is marked by arrows (original magnification, ϫ20). Diagnosis: Dicrocoelium dendriticum infestation The adult trematode D. dendriticum, or lancet fluke, lives in the gall bladder and bile ducts of their final hosts (ruminants— in particular, sheep). D. dendriticum eggs (figure 1), which are passed in the feces of the final host, are swallowed by terrestrial snails. In these primary intermediate hosts, miracidia develop into ceracaria within 3–4 months. A hatching miracidium from the patient's stool sample is shown in figure 2. Subsequently, the cercaria are excreted by the infected snails in " mucus balls. " These mucus balls are eaten by ants, and the swallowed cercaria settle in the suboesophageal ganglion of the ants. This ironically named, so-called " brainworm " affects the behavior of its secondary intermediate host dramatically; instead of returning home when the daytime temperature falls, the " brainwashed " ant ascends to the tip of a blade of grass. There, it clings in a state of tetania of its mandibular muscles to the vegetation and, thus, becomes an easy victim for herbivorous sheep and cattle, the definite hosts of D. dendriticum. In the intestinal tract of their mammalian host, metacercaria excyst from the ants and develop into young flukes, which migrate through the common bile duct into the liver. There, the adult dicrocoelia produce eggs (figure 1), thus completing their complex life cycle [1]. After ingestion of infected ants, humans may also become final hosts. This, however, is a quite rare phenomenon. In the vast majority of cases, the appearance of D. dendriticum eggs in human feces is due to ingestion of raw or half-cooked liver of infected animals (e.g., sheep). For example, in a study involving 208 patients from Saudi Arabia with D. dendriticum eggs in stool samples, only 7 patients had true infection [2]. Similarly, in an additional study from Saudi Arabia involving 1196 parasitologically investigated patients, only 32 of 121 patients with D. dendriticum eggs detected on microscopic examination of stool samples had true dicrocoeliosis, as determined by examination of additional stool samples obtained after 3 days of a liver-free diet [3]. In 77 egg-positive …