Abstract For several reasons, we are convinced that the parasitologist community must look again at porcine neonatal coccidiosis. We find it surprising that this ...
Parasitol Res (2000) 86: 834±837
Ó Springer-Verlag 2000
ORIGINAL PAPER
Guy-Pierre Martineau á JeÂroÃme del Castillo
Epidemiological, clinical and control investigations on ®eld porcine coccidiosis: clinical, epidemiological and parasitological paradigms?
Received: 2 February 2000 / Accepted: 4 February 2000
Abstract For several reasons, we are convinced that the parasitologist community must look again at porcine neonatal coccidiosis. We ®nd it surprising that this disease is seldom addressed, and that assumptions are not always supported by clinico-epidemiological analysis. For example, the relationship between diarrhoea and the excretion of oocysts during experimental infection versus ®eld infection is not questioned. Lindsay et al. review parasitological knowledge of this disease in the latest (1999) edition of Diseases of swine. Although this paper is divided into two parts, we have three distinct objectives: (1) to bring to the debate our experience in the medical control of this disease; (2) to propose a diagnostic methodology; (3) to raise some questions on various clinical, epidemiological and parasitological unknowns.
Why is there such discrepancy between parasitological, clinical and epidemiological knowledge? Various hypotheses can be put forward. But for us, what stands out is the fact that parasitological knowledge obtained by experimental challenge (Lindsay et al. 1980, 1982; Harleman and Meyer 1984) does not adequately explain some clinical and epidemiological ®eld characteristics. Many questions, in fact, remain unanswered. How, for instance, do we reconcile the Isospora suis cycle, the ecacy of toltrazuril administered once to 3- to 4-day-old piglets, and the onset of clinical signs at 10±12 days of age (Martineau et al. 1994a,b)? Another G.-P. Martineau Ecole Nationale VeÂteÂrinaire de Toulouse, 23 Chemin des Capelles, 31076 Toulouse Cedex, France J. del Castillo Faculte de meÂdecine veÂteÂrinaire de l'Universite de MontreÂal, C.P. 5000, St-Hyacinthe, QueÂbec, J2S 7C6 Canada
possible hypothesis is that clinical importance (prevalence) may be over-diagnosed. In this case, why is toltrazuril so eective in controlling such a characteristic pathological disease in piglets? ``Rare diseases are rare'' and coccidiosis is not a rare disease. In fact, it is very common. Nevertheless, information on its prevalence comes directly from the herds (not the diagnostic laboratory). Indeed, submissions to diagnostic laboratories of piglets with diarrhoea and/or diarrhoeic specimens for diagnosis of intestinal coccidiosis often prove negative (we will analyse some reasons). In addition, the laboratory's contribution in therapeutic orientation terms (e.g. the antibiogram in bacterial diseases) is minor. Results of individual coprological examinations are often deceptive, and can point to a neonatal colibacillosis diagnosis, or any other bacterial infectious disease. More often than not, laboratories are asked not to con®rm coccidiosis, but to identify the causal agent. Why are all litters not equally aected, as environmental contamination probably impacts all farrowing pens? One of the hypotheses gleaned from our work is that cross-fostered piglets shed earlier and may be responsible for ``over-contamination'' (Consequence of stress? Speci®c behaviour?) The severity and duration of diarrhoea are greater and earlier in cross-fostered piglets compared with resident counterparts, despite the fact that shedding is greater in the latter. Indeed, individual oocyst shedding among piglets from the same litter is seemingly in¯uenced by status within the litter (resident or adopted) (Fig. 1, Table 1). This hypothesis is compatible with seemingly solid immunity (Stuart et al. 1982), since adopted piglets would not therefore have the same degree of intestinal protection as resident counterparts. Why this dichotomy between individual stools in the same pen on the same day? We do not know. We have examined the relationship between the consistency of the stools and oocyst excretion (Table 1) (del Castillo et al. 1996a). It is clear that shedding can start before, after or even on the same day that clinical signs appear. It is also
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Fig. 1 Dynamic of sporocyst excretion in all piglets of the same litter between day 7 and day 12. Piglet no. 35 is cross-fostered (from del Castillo et al. 1996a)
Fig. 2 Interval between occurrence and diarrhoea and oocyst excretion. For example, the frequency 33% at day 1 means that oocyst shedding occurred 1 day before the onset of diarrhoea (from del Castillo et al. 1996a)
Table 1 Daily excretion of sporocysts in individual piglets of the same litter as illustrated in Fig. 1, according to the appearance of the stools (from del Castillo et al. 1996a) (S solid, P pasty, W watery). The grey zone corresponds to the excretion of oocysts
Why is there such a marked seasonal eect? The usual answer is that this is related to sporulation, which is easier and quicker in hot environmental conditions (less than 12 h at 32±35 °C, which is the norm in piglet pens). Nevertheless, thermal conditions in farrowing facilities vary little between winter and summer. Moreover, winter conditions in some areas (Brittany, for example) are very dierent from those in others (e.g. Quebec). Why is toltrazuril, given once orally at 3 days after birth, so eective even though contamination is probably low-level? We have already reported on the ecacy of toltrazuril in the control of ®eld cases of coccidiosis (Martineau et al. 1994a,b) (Table 2). Coprophagy in piglets (Sansom and Gleed 1981) and its relationship with the disease, drawn from clinical observations (Joyner et al. 1981) is often cited, as is skin contamination of the sow's mammary glands. On this point, we must demythologize the association between clinical coccidiosis and poor hygiene. Before the use of toltrazuril, empirical clinical works by an American swine practitioner, S. Henry, put this link in doubt. Environmental contamination has only been the subject of indirect analysis, such as the ecacy of some hygiene measures (e.g. painting the ¯oor of pens before each
Piglet's Age (days) identi®cation 7 8 30 29 33 25 26 32 27 34 35* 31
S S S S S S S S
S S S S S S L S
9 S S S S S P S S
10
11
S S
S
S S S
12
13
L P
S P P P
P L S
14
P
* Fostered
apparent (Table 1) that the daily evolution of the diarrhoea is chaotic: it can begin pasty and evolve to liquid or to solid, or vice versa. We are far away from the experimental observations (Roberts and Walker 1982; Stuart et al. 1982). In a large number of litters, the excretion of oocysts began before or concurrent with diarrhoea in over 75% of cases (Fig. 2) (del Castillo et al. 1996a). This observation does not support Lindsay et al.'s assumption that shedding occurs 2±3 days after the onset of diarrhoea. We hypothesize that this characteristic connects with the parasite's endogenous cycle. Thus, the relative importance of the dierent phases would vary according to the pressure of infestation. Experimental reproductions support this theory. These include the presence of different numbers of shedding periods according to the challenge (Harleman and Meyer 1984). Indeed, in experimental challenge, clinical signs occur 1±2 days after experimental infection (Stuart et al. 1982).
Table 2 Ecacy of toltrazuril on the shedding of oocysts between control litters (21 litters, 174 piglets) and toltrazuril-treated litters (56 litters, 530 piglets) in ®eld coccidiosis (Martineau et al. 1994a,b) (categorized analysis by Fisher's test p < 0.0001) Treatment
Positive* Negative**
Control
Toltrazuril
16 5
1 55
21
56
* Positive: ³25 OPG ** Negative:
