Clinical and biological properties
Our investigation found severe piglet diarrhea in one farm. The
morbidity rate of piglets was 30.65% (149/486), and the mortality rate
was 35.57% (53/149). To figure
out the agents of diarrhea in piglets, we collected fecal samples from
piglets with diarrhea and tested a variety of diarrhea-causing viruses
including Porcine epidemic diarrhea virus; Porcine deltacoronavirus;
Transmissible Gastroenteritis Virus; swine acute diarrhoea syndrome
coronavirus; porcine rotavirus; Porcine circovirus type 3 and Porcine
Circovirus-like Viruses by PCR methods, all the above pathogens could
not be detected. Excitingly, a β-hemolysis bacterium was isolated
(Fig.1A), which were Gram-stained negative, rod-shaped bacterium
(Fig.1B). The strain was purified by colonization, and named as GDHYZ30
strain. Subsequently, Koch postulates experiments were conducted to
verify the pathogenicity of the GDHYZ30 isolate. Nine 30-day-old healthy
piglets were randomly divided into three groups. 2ml of 3.5x10^9CFU
bacteria were administered orally or intramuscularly injected
respectively, and 2ml of PBS was administered orally to the control
group. At the second day, we found that all three piglets in the gavage
group developed diarrhea (Fig.1C). One piglet in the intramuscular
injection group had diarrhea and two piglets died. Piglets in the
control group were asymptomatic. Piglets with diarrhea had thin
intestinal walls and flatulence (Fig.1D). The GDHYZ30 strain could be
isolated from the blood and heart of the dead piglets, but not from the
piglets administered orally group. The above results indicated that the
GDHYZ30 strain was the pathogen causing piglet diarrhea and acute death.