The Latest on Pathogenesis and Control of Highly Pathogenic

PRRSV in ChinaHanchun Yang

College of Veterinary Medicine,

China Agricultural University, Beijing, China

2016-12-03

The emergence and prevalence of highly pathogenic PRRSV (HP-PRRSV) in 2006 in China

• High fever (41-42 )℃• High morbidity • High mortality• Severe abortion in sows• Severe respiratory disorders

in growing pigs

Outline

Pathological pathogenesis of HP-PRRSVMolecular basis of HP-PRRSV virulenceImmunosuppressive aspect of HP-PRRSV Evolution and diversity of PRRSV in ChinaControl of HP-PRRSV infection

1. Pathological pathogenesis of HP-PRRSV

1.1 HP-PRRSV infection causes acute lung injury

More serious lung injuries

Severe pathological lung lesions (increased neutrophils, mast cells and mononuclear)

Lung fibrosis

Fibrosis in the lungs

Histopathological changes in the lungs

Han et al., Vet. Microbiol. 2014.

Tissues with different virus distributions

JXwn06 group HB-1/3.9 GroupNumber of + or - Number of + or -

Trachea + 5/5 - 5/5Esophagus ++ 5/5 - 5/5Stomach ++ 5/5 +1/5Small/large intestine ++ 5/5 ++ 1/5Liver + 5/5 - 5/5Cerebrum +4/5 - 5/5Kidney ++ 5/5 +1/5Mandibular gland ++ 5/5 - 5/5Thyroid gland ++ 5/5 - 5/5

Li et al., Virol. J. 2012.

1.2 HP-PRRSV displays an expanded tissue tropism

HP-PRRSV can be detected from more tissues (by IHC)

10-1000 folds higher viral loads compared with LP-PRRSV

+ represents < 10 positive cells; ++ means > 10 positive cells

1.3 HP-PRRSV shows higher replication efficiency in vivo

HP-PRRSV (HuN4) infects alveolar epithelial cells, macrophages and vascular endothelial cells causing diffuse alveolar damage and lymph node necrosis.

HP-PRRSV shows higher replication rate in infected tissues

Hu et al., Transbound. Emerg. Dis. 2013.

Lungs (a) Mesenteric lymph node (b) Tonsil (c)

2. Molecular basis of HP-PRRSV virulence

HP-PRRSV displayed fatal virulence for pigs and the 30-aa deletion in nsp2 is not related to its fatal

virulence

Animal inoculation trials• 100% morbidity • Fatal virulence for all ages of

pigs

30-aa deletion in nsp2 as a molecular marker

Zhou et al., J. Virol. 2009.Zhou et al., Virus Res. 2010.

• Infectious cDNA

clone

• JXwn06-HP-PRRSV

• HB-1/3.9-LP-PRRSV

Systemically analyzing

pathogenicity• Rectal temperatures• Average daily gain • Clinical signs/scores• Gross lung lesions • Microscopic lesions• Mortality of pigs

Nsp9 and Nsp10 are related to the replication efficiency in vivo and contribute to the fatal virulence

of HP-PRRSV

Li et al., PLoS Pathog. 2014.

3. Immunosuppressive aspect of HP-PRRSV

Chen et al., Vet. Microbiol. 2014; Guo et al., Virology 2013; Han et al., Vet. Microbiol. 2014

HP-PRRSV infection significantly elevated levels of IL-1, IL-6 and TNF-α in sera of pigs

Highly expression of IL-1, TNF-α, IL-6 and IL-8 in the local lung tissues and in the microglia

A striking elevation in levels of cytokines associated with both innate and adaptive immunity

Leading “systemic cytokine shock” or “cytokine storm”

HP-PRRSV induces proinflammatory cytokines

Up-regulates the levels of IL-10 in sera of pigsLeads to a weakened cell-mediated immunity Not all the HP-PRRSV strains stimulates IL-10

expression Song et al., Dev. Comp. Immuno. 2013; Zhang et al., Virol. J. 2013. He et al., Virus Res. 2015.

He et al., Vet. Microbiol. 2012; Li et al., Virus Res. 2014；Wang et al., PLoS One 2015.

HuN4CH-1aMock

HuN4 3DPI HuN4 14DPI

CH-1a 3DPI Mock 3DPI

HP-PRRSV induced 40 times higher thymocytes apoptosis

Most of apoptotic cells were CD3+ T cells (non-infected)

HP-PRRSV was only found in CD14+ cells

HP-PRRSV causes thymus atrophy and the depletion of thymocytes of pigs

HP-PRRSV down-regulates SLA I expression on PAMs

PRRSV down-regulates SLA I on PAM surfaceJXwn06 (HP-PRRSV) > HB-1/3.9 (LP-PRRSV)

Du et al., J. Virol. 2016.

Target SLA I for degradation by ubiquitin-proteasome system

Nsp1α contributes to SLA I degradationNsp1α interacts with both chains of SLA IStructural integrity of nsp1α is required to induce SLA-

I-HC and β2m degradation

Du et al., J. Virol. 2016

HP-PRRSV suppressed Th17 cells response in vivo Suppressed Th17 cells

response in peripheral blood Caused a reduced Th17 cells

in lungs JXwn06 > HB-1/3.9 HP-PRRSV infection showed

higher bacterial loads in lungs

Zhang et al., Vet. Microbiol. 2016

4. Evolution and diversity of PRRSV in China

Diversity of PRRSV strains

Genotype 2 PRRSV• Multiple

lineages/subgroups/clades• Diversified strains• HP-PRRSV• LP-PRRSV• Field virus• Vaccine virus• Recombinant virus among field

virus or between field virus and vaccine virus

nsp2

Zhou et al., BioMed Res. Int. 2014.

At least 23 patterns of nsp2 deletion or insertions were found

Various strains of PRRSV with different deletion or/and insertion patterns in nsp2

21

NADC30-like virus is emerging and prevailing in China

Zhou et al., Emerg. Infect. Dis. 2015

CHsx1401 has 131-aa deletion identical to the NADC30

Deletion: 111-aa ( 323-433), 1-aa (481) and 19-aa (533-551)

Alignment of nsp2 amino acid sequence of CHsx1401and reference viruses

Introduction of NADC30-like PRRSV by breeding pigs.NADC30-like was evolved from NADC30 isolated in

2008 in the US.Prevalence of NADC30-like PRRSV in pig-producing

areas in China since 2014.Causing abortion of pregnant sows and respiratory

disorders in growing pigs on many pig farms.Virulent, but less virulence compared with HP-PRRSV.

NADC30-like virus has undergone genetic exchange with the HP-PRRSV

Zhao et al. J. Virol. 2015

1737 3506

A 2

3

4

5

6

71α 1β NSP2 NSP 3 4 5 6 7 8 9 10 11 12

2b 5a

Recombination analysis of TJnh1501

Recombinant virus between HP-PRRSV vaccine and NADC30-like virus was found

Unpublished data

5. Control of HP-PRRSV infection

Vaccination is a major measure for controlling PRRS in China

List of commercial HP-PRRSV-derived MLV vaccines in China

Safety concerns of MLV-derived from HP-PRRSV

Massive vaccinations on pig farms using HP-PRRSV MLV vaccines clearly have benefited the reduction of the outbreak and incidence of HP-PRRS in China.

Reproductive failures in the vaccinated sows.• Sporadic abortion• Increased stillbirth rate • Increased weak piglets Respiratory conditions in the vaccinated growing pigs.• Increased PRRS morbidity and mortality in nursery

pigs and finishing pigs The vaccine virus circulates and spreads on pig farms.

The pig farms with vaccination of HP-PRRSV-derived MLV vaccine showed clinical PRRS

• More than 5% of pregnant sows suffered abortion following vaccination using HP-PRRSV MLV vaccine.

• Increased stillbirth rate.• Nursery pigs showed clinical PRRS

two or three weeks following vaccination with HP-PRRSV MLV vaccine.

• Poor growth performance of pig herds in nursery and finishing stages.

• 20-30 % morbidity.• About 10-20% mortality in

growing pig herds.• The virus is “vaccine virus”.

NT1,2,3 VS JXA1-P80 Field strains Vaccine

Jiang et al. Vet. Microbiol 2015

Field strains are likely to be revertants of the vaccine strain JXA1-P80

The challenges facing the control of PRRS in China

Diversity of PRRSV strains

Continuing emergence of novel PRRSV strains

How to choose PRRSV MLV vaccines for PRRS

control

How to strategically use HP-PRRSV-derived MLV

vaccines (restrict or stop?)

Summary

HP-PRRSV infection causes severe lung lesions and expanded tissue lesions of pigs.

HP-PRRSV infection induces “cytokine storm”.HP-PRRSV has stronger ability of suppressing cell-

mediated immunity of pigs.Nsp9 and nsp10 together contribute to the fatal

virulence of HP-PRRSV.High replication efficiency in vivo of HP-PRRSV

contributes its high pathogenicity.Evolution and diversity of PRRSV is a great challenge

facing the control of PRRS in China.

Future work

Further understand the molecular pathogenesis of HP-PRRSV.

Reasonably and strategically use HP-PRRSV-derived MLV vaccines.

Push forward the elimination of PRRSV on breeding pig farms to construct PRRS-negative breeding herds/farms.

Implement regional elimination of PRRSV in China.

¤ A project on making authentication for

disease-eliminated breeding pig farmsAuthenticated by Chinese CADC

Including CFS, PRV and PRRS

Acknowledgments

Our study on PRRSV is supported by: Key and major project of National

Natural Science Funds from National

Natural Science Foundation of China

(31330077; 31490603)

National Key Basic Research Plan

Grant (2014CB542700)

The earmarked fund for Modern Agro-

industry Technology Research System

of China (CARS-36)

My research team:

Thank you for your attention !

THANK YOU FOR YOUR ATTENTION !