Animal models for emerging coronavirus: progress and new insights

Figures & data

Figure 1. Experimental animals of SARS-CoV, MERS-CoV and SARS-CoV-2. The coronaviruses with high infectivity and pathogenicity break the species barrier and infect human in the past two decades. Besides NHP, mice, hamsters, ferrets and rabbits, the other possible natural hosts might be able to support the studies of coronavirus infection, pathogenesis and drug discovery.

Table 1. Natural infectious animal model for SARS-CoV and MERS-CoV.

Animals	SARS-CoV	MERS-CoV
NHPs	Rhesus and cynomolgus macaques, African green monkeys, common marmosets, squirrel monkeys and mustached tamarins; clinical signs, viral replication and pathology degree varied on the species	Common marmosets have a more severe response to the virus with higher viral titres and severe pathology than rhesus macaques; lethality is only observed in common marmosets
Mice	Immunocompetent young inbred mice support transient infection without clinical illness	Not permissive for entry
Hamsters	Self-limiting infection; mild clinical illness	Not permissive for viral replication
Ferrets
Civet cats	Permissive to infection and replication; mild clinical illness	No report
Rabbits	No report	Infection with mild clinical illness
Camelidae	No report	Infection without clinical illness

Table 2. Representative receptor transgenic and transfected mice support SARS-CoV and MERS-CoV infection.

	SARS-CoV		MERS-CoV
	McCray et al. [31]	Tseng et al. [32]	Zhao et al. 2014	Agrawal et al. [35]	Li et al. [36]	Iwata-Yoshikawa et al. [37]
Background	C57BL6		C57BL6; BALB/c	C57BL6		BDF1 × C57BL6
Age (weeks)	6∼8	8∼20	6∼22	5∼7	6∼13	9∼25
Viral strains	Urbani		EMC/2012; EMC/Vero; MERSMA	EMC/2012; rMERS-CoV/RFP	EMC/2012; EMC/Vero; MERSMA	EMC/2012;
Inoculation dose	2.3 × 10^5 PFU	2 × 10^5 TCID50	1 × 10^5 PFU	1 × 10^6 TCID50	50∼5000 PFU	1 × 10^5 TCID50
Clinical illness	Severe pneumonia; weight loss; robust cytokine storm in lung and brain		Mild inflammatory cell infiltrates; weight loss	Severe pneumonia; weight loss; robust cytokine storm in lung and brain	Viral strain dependent; mild to severe pneumonia; weight loss; activation of innate immune cells	Mild pneumonia; weight loss; slight cytokine storm in lung and brain
Peak viral load	∼10^8 TCID50/g in lung at 4dpi	∼10^9 TCID50/g in lung and brain at 4dpi	∼10^7 PFU/g in lung at 2∼3dpi	∼10^8 TCID50/g in lung at 2dpi; ∼10^5 TCID50/g in brain at 4dpi;	Viral strain dependent; ∼10^8 PFU/g in lung at 1∼3dpi (5000 PFU of MERSMA)	∼10^5 TCID50/g in lung at 3dpi
Mortality rate	∼90% at 4 dpi	AC63 (None); AC70 (100% at 8 dpi)	None	100% at 6 dpi	Viral strain and inoculated dose dependent; 100% at 6 dpi (5000 PFU of MERSMA)	None

Figure 2. Mutations in MA stains of SARS-CoV and MERS-CoV. (A) Nucleic acid and amino acid mutations of SARS_MA strain MA15, MA20, and v2163 [39]. (B) Amino acid changes of MERS-CoV S1 (receptor binding) and S2 (fusion) domains of different plaques and clones of the EMC-P30 strain [36].

Table 3. Infection outcomes of mouse-adapted SARS-CoV strains.

Strains	Urbani (wt)	Urbani+S	Urbani+N9	Urbani+N9/S	MA15	MA+N9/S	MA20	v2163	Urbani	MA15
Mouse	One-year-old BALB/c						5∼10 week BALB/c
Inoculation dose	1 × 10^5 PFU								1 × 10^5.5 CCID50
Peak viral load in lung at 2∼4 dpi	∼10^5 PFU/g	∼10^7.2 PFU/g	∼10^8 PFU/g	∼10^7.5 PFU/g	∼10^6 PFU/g	∼10^6.5 PFU/g	∼10^6.5 PFU/g	∼10^7.5 PFU/g	∼10^5.8 CCID50/g	∼10^6.6 CCID50/g
Mortality rate	None	100% at 8dpi	None	100% at 4dpi	100% at 5dpi	100% at 4dpi	ND	100% at 6dpi	None	90% at10 dpi
Mean day of death (days)	–	6.0 ± 1.26	–	3.2 ± 0.44	3.8 ± 1.09	3.2 ± 0.40	ND	4.8 ± 1.8	–	6.8 ± 1.4
LD50	–	10E4.4	–	10E2.5	<10E2	10E2.3	ND	10E3.3	–	–

Table 4. Experimental animals for development of SARS-CoV and MERS-CoV vaccines.

Vaccine type	Design strategy	Animal models and examples		Advantages	Disadvantages
		SARS-CoV	MERS-CoV
Inactivated particle	Whole virus inactivated by heat, chemicals, or radiation	African green monkeys, rhesus and cynomolgus macaques; BALB/c, C57B6 and 129S6/SvEv mice; ferrets; rabbits	BALB/c mice	Rapid and easy for development; safety; high-titre NAbs; protective when used with adjuvant	Induction of inflammatory immune pathology and ADE; possibly incomplete protection
Live-attenuated particle	Attenuated the virulence by viral genome mutagenesis or targeted deletions	BALB/c mice; hACE2-Tg mice; hamsters	BALB/c mice	Inexpensive; quick immunity; less adverse effect; comprehensive activation of host immunity; multiple targets	Risk of phenotypic or genotypic reversion and disseminated infection in immunocompromised patients
Vector	Viral vectors that express S or the S1 subunit	BALB/c and 129S6/SvEv mice; hamsters; ferrets	BALB/c mice; hDPP4-Tg or transfected mice; dromedary camels	Comprehensive, Stronger and specific activation of host immunity; high-titre NAbs; safety	Varied and skewed immune responses; possibly incomplete protection
Virus-like particle	Virus-like replicon particles containing S protein	BALB/c mice	Ad-hDPP4 mice; BALB/c mice	Induction of antiviral T cell responses and S protein specific NAbs; reduce viral titres in lungs to nearly undetectable levels by one after inoculation with MERS-CoV	Varied and skewed immune responses; risk of ADE; possibly incomplete protection
Nanoparticle	Purified S protein-containing nanoparticles; Gold nanoparticle adjuvanted S protein	BALB/c mice	BALB/c mice	Induction of S protein specific NAbs	Need appropriate adjuvants; Varied and skewed immune responses; risk of ADE
Viral subunit	Antigenic components, whole or separate (S and N protein)	Rhesus macaques, BALB/c mice and rabbits	Rhesus macaques; hDPP4 transgenic mice; BALB/c mice	High safety; consistent production; Comprehensive, Stronger and specific activation of host immunity; high-titre NAbs	Uncertain cost-effectiveness; mild immunogenicity; need appropriate adjuvants; risk of ADE
DNA plasmid	DNA plasmids that encode S and N protein	BALB/c mice	Rhesus macaques and BALB/c mice; Ad-hDPP4 mice	Easier to design; high safety; high-titre NAbs	Lower and skewed immune responses; possibly delayed-type hypersensitivity

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