The survival capacities of Muellerius capillaris (Nematoda: Protostrongylidae) free-living larval stages (L1) of an Israeli desert isolate (Nubian isolate) (92 mm rain per annum) and a French isolate from a temperate habitat (650 mm rain per annum) were compared under humid and extreme dry conditions. Under the dry conditions (7% relative humidity [r.h.] and 33% r.h. at 23 °C), both isolates exhibited the same remarkable survival capacity for periods of 17 and 28 days, respectively (>92% survival, P>0·1). However, during and after recovery from the anhydrobiotic state, different behaviour patterns of L1 were observed in each isolate. Under humid conditions (97% r.h.) for 10 days, both isolates exhibited similarly low survival percentages (13·4±4·6%, S.E., survival for the Nubian isolate, 3±3% for the French isolate, P>0·05). In water, the French isolate was less active, survived better (52±8·4% vs 28·7±3·7, by day 28, P<0·05) and retained a better morphological appearance (shrunk less) than the Nubian isolate. Larval development of the French isolate in the land snail Theba pisana was significantly faster than that of the Nubian isolate, reaching a higher proportion of infective stages (L3) on day 36 post-infection (78·6% vs 56% P>0·05). However, similar infection intensities were recovered in snails infected with either of the isolates (59·8±10·3, S.E., n=14, for the French isolate, 53±6, n=13, for the Nubian isolate, P<0·05).

First-stage larvae of pure strains of M. capillaris and N. linearis (Nematoda: Protostrongylidae) from goats were used to assess the influence of rapid desiccation on survival. M. capillaris survived desiccation of faeces better than N. linearis. The latter species was particularly susceptible to duration of storage after desiccation (0 to 10 days). Surviving larvae of desiccated batches of M. capillaris were less able to infect the land-snail Candidula intersecta. Resistance of first-stage larvae to desiccation is a key factor in infectivity and may partly account for the geographical distribution of the two species of protostrongylids.

Muellerius capillaris was the only species of nematode recovered from the lungs of young and adult sheep and goats of north-east Zaire. The prevalences were of 19% (sheep) and 32% (goats). The slug Atoxon pallens contained larvae in natural conditions and represents a potential intermediate host. The land snails Achatinidae (Achatina stuhlmanni and Limicolaria spp.) could not be experimentally infected with M. capillaris larvae.

The rediae of Fasciola hepatica were counted according to generation in adult and juvenile Lymnaea truncatula following single infection with Fasciola hepatica, double infection with F. hepatica and then Muellerius capillaris, or double infection with M. capillaris and F. hepatica. The rediae found in double infections were essentially first generation and an early cohort from the second generation. The following differences were observed in adult snails which underwent double infection when compared to corresponding single infections: i) dependent rediae were almost completely absent; ii) degenerating independent rediae were found in identical or decreased numbers; iii) living independent rediae of the first generation were decreased in number, while those of the second generation had variable decreased numbers. The results were similar in juvenile snails with double infections, except that the numbers of degenerating independent rediae were higher than those found in corresponding single infections and the numbers of rediae of the second generation were increased. The order of exposure in double infections had no influence on the number and maturation of fasciolid rediae.