Monitoring Angiostrongylus vasorum natural infection in dogs under parasitic treatment.

Angiostrongylus vasorum is a nematode which causes a potentially fatal chronic parasitic pneumonia in dogs. A. vasorum infection is considered endemic in various parts of Europe (Koch and Willesen, 2009) and in Italy it is recently assumig increasing importance. Aim- To monitor A. vasorum natural infection in dogs under treatment by direct microscopy and modified Baermann technique on faecal samples. Materials and methods- Owned dogs presented at the Clinical Unit of the Veterinary Faculty of Bari, Italy, and positive to A. vasorum infection were included in the study. The diagnosis was reached by means of L1 detection on direct faecal smear and/or using the modified Baermann technique. Faecal samples positive to nematodes mobile larvae were sent to the Parasitology Unit for morphological identification. The animals were treated and clinically and parasitologically monitored. Asymptomatic dogs were treated with an imidacloprid/moxidectin spot-on formulation (Im/Mox) at T0, T+15,T+30. Symptomatic dogs were treated with fenbendazole 25 mg/kg/ bid/os for 21 days. Treatment was weekly monitored using Baermann test on three days faecal pool both in symptomatic and asymptomatic animals for one month, than once a month till possible. When infection persisted a second-line treatment was considered. In symptomatic animals clinical examination was performed once a week till clinical recovery than twice a month, while asymptomatic animals were revaluated only after the third spot-on treatment. Results- Ten dogs were enrolled in the study. Signalment, clinical signs at presentation, therapy, clinical remission time and results of faecal monitoring are reported in table. Briefly 5 dogs were treated with fenbendazole and the others with Im/Mox. In three dogs a second-line treatment was needed and fenbendazole 25 mg/kg/die for 21 days associated to Im/Mox was used. In these three dogs a long term monitoring was possible. Conclusions- Given its proven efficacy (Chapman et al., 2004) fenbendazole has been used in symptomatic patients, whereas Im/Mox, more recently proposed (Willesen et al., 2007) was used for asymptomatic dogs. All dogs treated with fenbendazole (dog 6-10) resulted negative at Baermann after 1-2 weeks of treatment but a long term monitoring was available only in two dogs (dog 6,7) showing negative results. A highly variable response was registered in dogs treated with Im/Mox (dog 1-5). Two dogs (dog 1 and 4) reached negative results 1-2 weeks after first spot-on administration and persisted negative for 16 and 20 weeks respectively. It is reported that larval excretion may continue for over 3 weeks, even if anthelmintic treatment was successful (Schnyder et al., 2010). Differently one case (dog 5) slowly reached negative results (8 weeks after the first spot-on) but it reverse newly positive two times during monitoring. Other two cases (dog 2 and 3) resulted persistently positive for 12 weeks. The last three dogs were treated with the second-line treatment. Cases 2 and 3 achieved negative results so slowly (8 and 20 weeks after second-line treatment) to make difficult a direct association with treatment efficacy, anyway they persisted negative in a long term follow up. Case 5 showed negative results 4 weeks after second-line treatment but unexpectedly it reverse positive a second time. Reinfection or infection not controlled? The question is open, we can only make assumptions. It is already known that anthelmintic treatments may not completely eliminate adult worms but be able to sterilise them leading to a reduced pathogenicity of A. vasorum infection (in: Schnyder et al., 2010). In experimental studies (Schnyder et al., 2010) on dogs treated with Im/Mox spot-on and untreated, eggs and larvae were only present in untreated dogs. The highly variable response registered in this study suggests that in natural conditions several factors could affect the response to treatment probably associated to the host and/or to the parasite. Moreover to monitor the response to treatment serial tests are needed; the limits of Baermann test are known and a single negative result does not mean control of infection.