Avoiding bias in parasite excretion estimates: the effect of sampling time and type of faeces

Abstract

The study of host-parasite relationships usually requires reliable estimates of parasite intensity, which is often estimated from parasite propagule concentration in faeces. However, parasite excretion in faeces may be subject to variation due to endogenous or exogenous factors that must be identified to obtain reliable results. We analysed the effect of the hour of sample collection on propagule counts of 2 intestinal parasites infecting the red-legged partridge: the capillarid nematode Aonchoteca caudinflata and coccidia of the genus Eimeria (Protozoa). Also, we test whether there are differences in propagule counts between caecal and intestinal faeces. Individual faecal samples from infected birds were collected daily at 4 different hours during several days. The hour of the day exerted a very strong effect on propagule counts, excretion of both types of parasites showing a clear and constant increase from dawn to dusk. Also, capillarid eggs were more abundant in intestinal than in caecal faeces, whereas the inverse pattern was found for coccidian oocysts. Standardization of the hour of sample collection or statistical control of this variable is recommendable to prevent bias. Similarly, in bird species with long caeca, consistent collection of one type of faeces may avoid significant errors in parasite burden estimates.

Prevalencia parasitaria en el gorrión altiplanero (Spizella wortheni): especie endémica de México y en peligro de extinción

“…Sin embargo, los resultados obtenidos en este estudio deberían tomarse con precaución, dado que el conteo de parásitos intestinales puede variar dependiendo del método de muestreo (Villanúa et al 2006). Asimismo, un estudio más extensivo debería realizarse en la mayor parte de su distribución, incluyendo áreas sub-urbanas donde el gorrión coexiste con aves de corral, y podrían representar un mayor riesgo de infección (Deem et al 2012) y a lo largo de la época reproductiva, cuando, dado el esfuerzo y desgaste energético asociado, las aves son más susceptibles a éstas debido a la inmunosupresión.…”

Sex-Specific Effects of High Yolk Androgen Levels on Constitutive and Cell-Mediated Immune Responses in Nestlings of an Altricial Passerine

“…Quantitative analysis of coccidian oocysts found in each fecal sample was carried out with a flotation technique (Villanúa et al 2006). Fecal samples were extracted from collection tubes and extended in filter paper for 5 min to remove formaldehyde remnants.…”

Gastrointestinal helminths may affect host susceptibility to anthrax through seasonal immune trade-offs

“…For animals that were not observed defecating, we collected fecal samples when possible by inserting a gloved hand into the rectum. As capture events took place between 9:00 and 14:00, fecal samples were collected within this same time window, thereby controlling for potential differences in timing of fecal egg shedding [67].…”