Table 1.

Enterovirus 71 animal models for pathogenesis studies

Animal	Virus strain	Infection route/dose	Clinical manifestation of animals and viral replication sites	Ref. No.
Non-human primates
Cynomolgus monkey	Clinical isolates and prototype BrCr	i.s./106 CCID50	The monkeys developed neurological manifestations including both pyramidal and extrapyramidal tract signs, such as flaccid paralysis, tremor and ataxia. The virus replicated in the spinal cord, brainstem, cerebella and cerebrum. EV71 had a wider neurotropism than that of polioviruses.	[19,20,27,28]
		i.v./105.5 to 107 TCID50
Rhesus monkey, adult and neonate	Clinical isolate (FY-23, C4 genotype)	i.c., i.v./106.5 CCID50	The infected adult monkeys developed CNS infection and neuron impairment with extra-neuronal pathological changes confined to the lung tissues and not the pancreas and spleen, where high viral loads were detected.	[2,29,30]
		i.t./ 104.5 CCID50	In neonate monkeys, HFMD-liked papules and vesicles were found on the limbs and in the mouth after intratracheal infection. However, the typical neurological complication was not observed. High viral titers were transiently detected in the brown adipose tissue, skeletal muscle and CNS.
		oral/106.5 CCID50 twice
Mice - immunocompetent
ICR, 1- to 14-day-old	Mouse-adapted EV71 strain (MP4, C2 genotype)	oral/5 × 106 pfu	The mice developed rear limb paralysis (with massive and widespread necrotizing myositis) and neuropathologies (with neuronal loss and apoptosis) in the spinal cord and brainstem before death. The spinal cord, brain and muscle were the major organs for virus replication in the late phase of infection. Retrograde axonal transport in neurons might represent the major transmission route of EV71 in mice.	[7,13,36,38,39]
		i.m./5 × 103 pfu
		i.c./5 × 104 pfu
BALB/c, 1- to 7-day-old	Mouse-adapted strain (MP-26 M)	i.c. /3.4 × 104 TCID50	The mice developed limb paralysis followed by death after MP-26 M infection. Skeletal muscle displayed severe necrotizing myositis and contained a high viral load. Viruses were also isolated from the blood, hearts, livers, spleens and brains of infected mice. The VP1 mutation (G145E) alone was sufficient to increase the virulence of the virus in mice.	[33]
		i.m./3.4 × 103 TCID50
		i.p./3.4 × 104 TCID50
ICR, 2-week-old	Mouse-adapted strain (MAVs, B3 genotype)	i.c., i.p., s.c., oral/105 CCID50	The mice developed paralysis followed by death after i.c., i.p., s.c. and i.m. administration but not after oral inoculation of the virus. The highest viral titers were detected in the skeletal muscle, spleen and spinal cord. The virus might enter the CNS via peripheral motor nerves after skeletal muscle infection.	[37]
		i.m./3 × 105 CCID50
ICR, 1-day-old	Mouse muscle-adapted strain (Fuyang-0805a, C4 genotype)	i.p./105 TCID50	The Fuyang-0805a strain showed strong myotropism and induced severe necrotizing myositis in both skeletal and cardiac muscles. The virus was detected in the muscle, heart and intestines.	[42]
Mice - immunodeficiency
NOD/SCID, 3- to 4-week old	NOD/SCID mouse-adapted strain	i.c./106 CCID50	The infected mice showed paralysis of the hind limbs. Viral RNA was first detected in the CNS and serum and then high copy numbers were detected in the heart, skeletal muscle and spinal cord.	[34]
	(EV71(NOD/SCID), B1 genotype)
AG129, 10-week-old	A129 and AG129 mouse-adapted strain (B2 genotype)	i.p./5.2 × 104 TCID50	The infected AG129 mice but not A129 mice developed limb paralysis, eye irritation, loss of balance and control of movements and exhibited high mortality.	[43]
AG129, 2-week-old	Clinical isolate (5865/SIN/00009, B4 genotype)	i.p./106 pfu	The infected mice displayed progressive limb paralysis before death. The virus accumulated in the CNS and resulted in massive damage in the limb muscles, brainstem and anterior horn of spinal cord. Low viral particles in the limbs after oral inoculation indicated that the paralysis was a consequence of EV71 neuroinvasion.	[32]
		oral/107 pfu
Gerbils, 21-day-old	Clinical isolate (EV71/58301, C4 genotype)	i.p./105 TCID50	The infected animals developed neurological disorders such as hind limb paralysis, slowness, and ataxia before death. Significantly high viral titers were detected in the spinal cord, brainstem and skeletal muscle.	[44]
Transgenic mice
PSGL-1, 10-day-old	Clinical isolates C4 genotype and Mouse muscle-adapted strain (Fuyang-0805a, C4 genotype)	i.p./108 TCID50	The transgenic mice were only susceptible to a mouse muscle-adapted EV71 strain and not the EV71 clinical isolates and exhibited severe symptoms that were comparable to those of the wild-type mice upon EV71 infection. High viral titers were detected in the muscle, spinal cord and brain after mouse-adapted virus infection. This study concluded that human PSGL-1 alone was not sufficient to provoke the infectivity of EV71 in mice.	[50]
SCARB2, 1- to 14-day-old	Clinical isolates, C2, C4, B4 and B5 genotypes and CA16	s.c./3 × 104 to 106 pfu	EV71 B genotypes were capable of inducing HFMD-like lesions and neurological disease with limb paralysis in 1-day-old but not transgenic mice older than 2 weeks of age. In contrast, 7- and 14-day-old but not 21-day-old transgenic mice were more susceptible to the C genotypes of EV71 and coxsackievirus A16 and exhibited more severe CNS diseases, limb paralysis and death than did the non-transgenic mice.	[52]
SCARB2, 3-week-old	Clinical isolates (Isehara/Japan/99, C genotype)	i.c., i.v., i.p., oral/ 104 to 106 TCID50	The transgenic mice displayed ataxia, paralysis and death. The CNS, including the spinal cord, brainstem, cerebellum, cerebrum, hypothalamus and thalamus, was the major replication site for the virus.	[35]

i.s.: intraspinal; i.v.: intravenous; i.c.: intracranial/intracerebral; i.t.: intratracheally; i.p.: intraperitoneal; s.c.: subcutaneous.