Abstract
BackgroundTo reduce environmental contamination with Toxocara canis eggs, the current general advice is to deworm all dogs older than six months on average four times a year. However, only a small proportion of non-juvenile household dogs actually shed T. canis eggs, and some dogs shed eggs more frequently than others. The identification of these frequent shedders and the associated risk factors is an important cornerstone for constructing evidence-based deworming regimens. The purpose of this study is to identify risk factors associated with recurrence of periods of shedding Toxocara eggs in a cohort of household dogs older than six months.MethodsWe performed a prospective study (July 2011 to October 2014) on shedding Toxocara eggs in a cohort of 938 household dogs older than six months from all over the Netherlands. The median follow-up time was 14 months. Monthly, owners sent faecal samples of their dogs for Toxocara testing and completed a questionnaire. Dogs were dewormed only after diagnosis of a patent infection (PI). Survival analysis was used to assess factors influencing the time to first diagnosed PIs (FPI) and the time to recurrent PIs (RPI).ResultsThe overall prevalence of PIs was 4.5 %, resulting in an estimated average incidence of 0.54 PIs/dog/year. No PI was diagnosed in 67.9 % of the dogs, 17.5 % of the dogs went through only one PI and 14.6 % had > 1 PI. Prevalence of PIs always peaked during wintertime. Increased hazards for first diagnosed PIs were associated with coprophagy, geophagy, walking off-leash for ≥ 80 % of walking time, reported worms in the faeces, feeding a commercial diet and suffering from urologic or respiratory conditions. Median time to reinfection was nine months. Factors associated with increased hazards for recurrent PIs were taking corticosteroids, changing dog’s main purpose, and proxies for veterinary care-seeking behaviours.ConclusionsWe concluded that targeted anthelmintic treatments in household dogs may be feasible as PIs tend to (re)occur in specific periods and in groups of dogs at high risk. Moreover, recurrent PIs appear to be influenced more by factors related to impaired immunity than environmental exposure to Toxocara eggs.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1816-7) contains supplementary material, which is available to authorized users.
Highlights
To reduce environmental contamination with Toxocara canis eggs, the current general advice is to deworm all dogs older than six months on average four times a year
Following a large cohort of dogs, all older than six months, up to three years without performing routine deworming in absence of a confirmed diagnosis revealed that approximately 68 % of dogs never tested positive for Toxocara eggs
The incidence rate of recurrent PIs (RPI) was much higher than that of first diagnosed PIs (FPI), suggesting that there is a group of dogs prone to recurrence of patent Toxocara infections
Summary
To reduce environmental contamination with Toxocara canis eggs, the current general advice is to deworm all dogs older than six months on average four times a year. Adult T. canis worms live in the intestine of dogs and other canids, laying eggs that pass into the faeces and contaminate the environment [5]. Within these eggs, a third-stage larva develops, after which the eggs are infective. The ingestion of infective eggs by older dogs (> six months of age) is less likely to lead to patent infections, as dogs develop immunity against the Nijsse et al Parasites & Vectors (2016) 9:531 tracheal migration of the larvae [8, 9], resulting in so-called somatic migration [10]. The uptake of low numbers of infective eggs [9, 11, 12] or the infection with larvae (rather than infective eggs) by consumption of raw meat and offal from infected paratenic hosts can lead to patent infections in adult dogs due to the evasion or avoidance of acquired immunity on lung level [10]
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