The migration and development of Filaroides hirthi larvae in dogs

Abstract

SUMMARYThe development of Filaroides hirthi has been shown to proceed through all 5 stages in the lungs of experimental dogs and the attendant morphological changes are described and illustrated. These observations are interpreted as proof that the unhatched larva of F. hirthi is the 1st stage and that the 1st stage is infective. Moults occurred at approximately 1, 2, 6 and 9 days after infection in the lung tissue. Larvae also developed in vitro to the doubly ensheathed 3rd stage which is the stage achieved by heteroxenous metastrongyloids in their molluscan intermediate hosts. The arrival of 1st-stage larvae in the lungs as early as 6h after oral administration and the anatomical distribution of larvae during the first 24 h indicates that larvae are transported from the alimentary tract to the lungs by way of the hepatic portal circulation, the mesenteric lymphatic drainage, or both. First-stage larvae and eggs containing 1st-stage larvae, when injected into the jugular vein, developed into adult F. hirthi lung- worms in the usual 5 week pre-patent period. This was interpreted as demonstrating that the canine alimentary canal, although undoubtedly the normal portal of entry, is not a site of reactions indispensable to the activation or development of the larvae. Eggs containing 1st-stage larvae, when introduced by jugular and portal venous and mesenteric lymphatic routes, yielded equivalent numbers of adult lungworms indicating that neither the hepatic capillary bed nor the mesenteric lymph nodes presented quantitatively significant impediments to their passage. The question is raised whether the mesenteric lymphatics really are the exclusive migration pathways of certain other species of metastrongyloid larvae. The suggestion is made that conventional studies based on the anatomical/time distribution of larvae be supplemented by intravascular experiments like those described in this report, to provide an independent line of evidence.

Emerging canine angiostrongylosis in northern England: five fatal cases

“…Larvae of other metastrongyles, such as C vulpis, F osleri and F hirthi are smaller at 250 to 300 μm in length (McGarry and others 1995, Ridyard 2005). Furthermore, larvae of F hirthi do not possess a prominent dorsal appendage (Georgi and others 1979), F osleri possesses an S-shaped tail (Urquhart and others 1954) and the larval tail of C vulpis is simply pointed. Taken together, the results of the pathological and parasitological examinations, and the clinical and life history data, confirm that A vasorum is endemic in dogs in the Lancashire region.…”

Emerging canine angiostrongylosis in northern England: five fatal cases

“…In the cases described here, A vasorum was identified based on the morphological features and the size of the parasites (larvae and adults) (Guilhon and Cens 1973), and the location of the adults in pulmonary vessels. Furthermore, A vasorum is so far the only metastrongyle in canids in the UK that has been identified within the pulmonary vessels (Urquhart and others 1954, Georgi and Anderson 1975, Georgi and others 1979, McGarry and others 1995). The adults of other, rare metastrongyles such as a Filaroides hirthi , are found in nodules in the lung parenchyma (Georgi and Anderson 1975, Georgi and others 1979); Filaroides osleri are found in nodules in the trachea and its branches (Urquhart and others 1954), and adult Crenosoma vulpis live in the mucosa of the bronchi (McGarry and others 1995).…”

Filaroidosis infection in an immunocompetent adult dog from France

“…For the treatment of dog Filaroides infections, the effective use of fenbendazole (50 mg/kg oral once a day for 10 to 14 days), albendazole (25 to 50 mg/kg twice a day for fi ve consecutive days repeated two weeks later), and single administration of injectable ivermectin at 0.4 -1 mg/kg, has been reported in previous studies (Bauer & Bahnemann,1996;Bowman, 2000;Caro-Vadillo et al, 2005). The treatment of F. hirthi is particularly challenging because this parasite does not require an intermediate host for its development, and reinfections and auto-reinfections frequently occur (Georgi et al, 1979;Torgerson et al, 1997). This was the main reason why milbemycin oxime and ivermectin treatments were performed in this case report.…”

“…Unlike other dog metastrongylid nematodes, F. hirthi has a direct life cycle. Puppies are infected through ingestion of fi rst-stage larvae (L1s) passed by the faeces of chronically infected bitches (Georgi et al, 1979). L1s rapidly make their way to the lungs via the he-patic-portal or mesenteric lymphatic system and can survive within the mesenteric lymph nodes for extended periods, thus exposing the animal to auto-reinfection (Georgi et al, 1979).…”

“…Puppies are infected through ingestion of fi rst-stage larvae (L1s) passed by the faeces of chronically infected bitches (Georgi et al, 1979). L1s rapidly make their way to the lungs via the he-patic-portal or mesenteric lymphatic system and can survive within the mesenteric lymph nodes for extended periods, thus exposing the animal to auto-reinfection (Georgi et al, 1979). Once in the respiratory apparatus, larvae moult into adults and within around fi ve weeks, females shed larvae that can be detected in the faeces of the infected host (Bowman, 2000).…”