Table 7.

Attempts to induce clinical disease in horses after inoculation with S. neurona.

No.	Type	S. neurona	Clinical disease	Durati on (days)	Diagnosis		Reference
					Bioassay	Histology
5	3–6 month foals	Naturally infected opossums (NIO)	Clinical signs in all, 28–42 DPI, neurological, lesions in spinal cord of 4	40–110	Negative	Negative	Fenger et al. (1997)
8a	3–4 years	NIO	lesions spinal cord in 7 of 8 horses	90	Negative	Negative	Cutler et al. (2001)
9a	Foals	NIO	Clinical signs more severe in stressedb horses	44–63	Negative	Negative	Saville et al. (2001)
20a	4–5 month old	Experimentally infected opossums (EIO)d	Dose response 100, 1000, 10000,100000, 1000000, 4 horses per group. Clinical signs in all, histologic lesions inconsistent	30	Negative	Negative	Sofaly et al. (2002)
24a	4–5 month old	EIOd	Stressed horsesb, second timec	40	Negative	Negative	Saville et al. (2004a)
6		EIOd	100–1000 sporocysts daily for 112 days		Positive, blood of 1 horse	No data	Rossano et al. (2005b)
1	Arabian 5-month old SCID foal	NIO	Knuckling 39 DPI, euthanized 53 DPI. S. neurona isolated from brain and blood	53	Positive		Long et al. (2002)
2	Arabian	NIO	Neurological signs in 1	90	Negative	Negative	Sellon et al. (2004b)
4	Arabian	500 million merozoites from culture, inoculated intravenously	3 horses neurological	41, 73, 80, 471	Positive in 1 horse brain	Negative
1	Arabian SCID foals	500 million merozoites from culture, inoculated intravenously in to 1 foal	NO clinical signs	21,32	Li, Sp,Sk of 1 foal, H and Sk of second foal	Negative
2	Arabian SCID foals	NIO	NO clinical signs	96	Li, Lu, Sp, H, Sk	Negative
5		500000 to 5000000 merozoites inoculated intrathecally	NO clinical signs	132	Not done	Negative	Lindsay et al. (2000c)
6		6000 merozoites in lymphocytes were inoculated intravenously daily for 14 days	All horses developed clinical signs	90	Not done	Positive	Ellison et al. (2004)
8		6000 merozoites from culture inoculated intravenously, daily for 14 days.	All horses developed clinical signs	55	Not done	No data	Witonsky et al. (2008)
5a		625,000 sporocysts NIO	Mild ataxia in 3	84		Negative	MacKay et al. (2008)

^ahorses obtained from Northwest Canada outside the range of opossums.

^bTransport stress model. Horses transported for 55 hours and dosed soon after arrival.

^cHorses transported after rest period.

^dIsolate SN-37R—obtained by serial passage between laboratory raised opossums and raccoons.

SCID= severe combined immunodeficiency disease.

H=heart, Li=liver,Lu=lung, Sk=skeletal muscle, Sp=spleen.