[Biological cycle of Paralibyostrongylus hebrenicutus (Nematoda: Trichostrongylidae)].

Paralibyostrongylus hebrenicutus accomplishes its life cycle spontaneously in captive Atherurus africanus, its natural host, and in experimentally infected guinea pigs and rabbits. Morphogenesis and larval morphology were studied in the guinea pig and described herein. Host infection were achieved either by subcutaneous or by oral inoculation. The entsheathed infective larvae moult soon after penetration in the vertebrate host. Following subcutaneous inoculation, they reach the lungs very probably through the lymphatic vessels and the right heart at H8, and the stomach as soon as D2. However, a possible direct migration by the mesenteric lymphatic vessels and crossing of the digestive wall cannot be excluded as a few larvae were found in the peristomachal mesentery. Following ingestion, L3 larvae reached the stomach directly. 24 hours post-ingestion, they were localized deep inside the gastric mucosa crypts lumen. The same larval localization was observed at D3 after a subcutaneous inoculation. At D5, regardless of the inoculation route, larvae reached their definitive position, embedded in the gastric mucosa mucus lining, where they underwent the 3rd moulting (L3-L4) followed by the 4th moulting (L4-Ad) at D19. Eggs appeared at D28. Except for the inflammatory granuloma seen in the lungs and the mesentery from H24 to D3, the nematode induced no tissue lesion. The genus Paralibyostrongylus is one of the most primitive in the Libyostrongylinae-Cooperiinae line. The double transmission route, may have made possible the transition from primitive cycles by cutaneous penetration to more specialized cycles by the oral route, the latter being responsible for the evolutionary success of the group in large herbivores.