Adult parasite burden and excretion of first-stage larvae of Angiostrongylus vasorum in dogs: Methodologically relevant diagnostic aspects and associations with serological detection of parasite antigen and specific antibodies.

Angiostrongylus vasorum is a widely distributed cardiopulmonary parasite of canids in Europe. Clinical signs in dogs can be highly variable and diagnostically challenging. A correct and early diagnosis is hence indispensable to adequately manage affected patients. First-stage larvae (L1) are excreted in the faeces of definitive hosts and conventionally identified using the Baermann technique. Moreover, ELISAs for the detection of circulating antigen and specific antibodies have been presented. The current study aimed at i) quantitatively assessing larval migration in the Baermann funnel after 12 h and 24 h; ii) investigating the influence of sample storage at 4 °C over the course of three days on the number of detected L1; iii) evaluating potential associations of adult worm burdens with larval shedding in dogs and ELISA optical density (OD) values for circulating parasite antigen and specific antibodies. Faecal samples were obtained from naturally infected dogs (n = 21) and Baermann funnels were set up in duplicate over the course of four consecutive days (days 0-3) starting with the day of sample collection. Funnels were harvested on days 1-4 after 12 and 24 h, respectively, and the number of L1 per gram faeces (LPG) was determined. The LPG did not differ between larval harvest after 12 h from harvest after 24 h. Storage of faecal samples at 4 °C for two and three days entailed a considerable decrease in LPG. Adult worm burdens and larval excretion data from previous experiments demonstrated a correlation between worm burden and LPG. In contrast, no correlations between worm burden and the level of parasite antigen and specific antibody OD values, respectively, were identified. Thus, OD values of both antigen and antibody ELISA did not allow for conclusions on infection intensity reflected by the number of adult parasites. For the detection of L1 in faeces, 12 or 24 h of larval migration time was not discriminating for A. vasorum positivity. Thus, early processing of faecal samples is essential, since larval detection and hence sensitivity of the approach considerably decreased over the course of three days of storage. Therefore, the common recommendation to collect faecal samples for three consecutive days and to subsequently analyse them needs to be reconsidered. The results of this study can be readily translated into precise recommendations for daily practice to adequately assess A. vasorum infected dogs.
Competing Interests: Conflict of interest The authors have no conflict of interest to declare.
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