Population biology studies on Isospora suis in piglets.

Abstract

Isospora suis may cause disease and economic loss in intensive piglet production units. Field studies have shown that litter mates develop varying severeness of isosporosis although initial infection pressure is considered to be identical in a particular farrowing pen. Experimental studies were conducted to evaluate the course of isosporosis under controlled clinical conditions. Piglets artificially infected at the age of 3 days each with 104 sporulated I. suis oocysts suffered from diarrhea from 2 days post infection (dpi) until 9 dpi while oocyst excretion lasted from 6 to 13 dpi. A lower infection dose (1×103 oocysts) resulted in onset of diarrhea at 6 dpi with a prolonged period of disease (10 days) and of oocyst excretion (4-16 dpi). The application of only 100 oocysts within 24 hours after birth caused severe disease starting at 7 dpi. Clinical isosporosis lasted for 6 days and oocysts were excreted from 5 to 14 dpi. Infection at an age of 11 days induced mild diarrhea for a maximum period of 2 days and only few oocysts were detected at 4 to 6 dpi, in one piglet from 7 to 9 dpi. It is concluded that the course of isosporosis is less related to the infective dose than to the age of the piglets. Artificial infection of 30 % of a litter with 1x103 oocysts per piglet at the age of 3 days resulted in rapid spread of isosporosis across the whole litter. However, oocyst excretion and clinical disease was less pronounced on a litter base when only two piglets initially received a low dose of 100 oocysts. Thus, initial contamination of the farrowing pen is obviously related to the course of isosporosis in the respective litter.