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Volume 18, Number 5—May 2012

Research

Characterization of Virulent West Nile Virus Kunjin Strain, Australia, 2011

Melinda J. Frost1, Jing Zhang1, Judith H. Edmonds1, Natalie A. Prow1, Xingnian Gu, Rodney Davis, Christine Hornitzky, Kathleen E. Arzey, Deborah Finlaison, Paul Hick, Andrew Read, Jody Hobson-Peters, Fiona J. May, Stephen L. Doggett, John Haniotis, Richard C. Russell, Roy A. Hall2, Alexander A. Khromykh2, and Peter D. Kirkland2Comments to Author 
Author affiliations: Elizabeth Macarthur Agriculture Institute, Menangle, New South Wales, Australia (M.J. Frost, J. Zhang, X. Gu, R. Davis, C. Hornitzky, K.E. Arzey, D. Finlaison, P. Hick, A. Read, P.D. Kirkland); The University of Queensland, St Lucia, Queensland, Australia (J.H. Edmonds, N.A Prow, J. Hobson-Peters, F.J. May, R.A. Hall, A. A. Khromykh); University of Sydney and Westmead Hospital, Westmead, New South Wales, Australia (S.L. Doggett, J. Haniotis, R.C. Russell)

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Table 3

Neutralizing titers of serum samples from WNV–infected horses against 3 WNV strains, Australia, 2011*

Horse serum samples % Inhibition of CPE/growth†
WNVNSW2011, 100 infectious units
   WNVKUN, 26 infectious units
   WNVNY99, 32 infectious units
80‡ 100§ 80 100 80 100
Control¶                
1 <20 <20   <20 <20   <20 <20
2 <20 <20   <20 <20   <20 <20
3 <20 <20   <20 <20   <20 <20
4 <20 <20   <20 <20   <20 <20
5 <20 <20   <20 <20   <20 <20
NSW#                
04 640 320   1,280 1,280   640 320
06 320 160   640 640   1,280 160
08 320 320   1,280 1,280   640 640
28 320 320   640 640   320 320
36 320 160   640 640   320 640
NT**                
111473 80 20   640 320   160 160
104714 320 80   640 640   640 640
110910 80 40   160 160   160 160
98727 40 40   160 160   80 80
WNV††                
1 160 40   640 40   320 320
2 320 160   1,280 640   160 160
3 80 160   320 320   640 640
4 40 20   160 160   320 320
5 320 80   1,280 320   640 640
mAb 3.91D‡‡ >2,560 >2,560   >2,560 >2,560   >2,560 >2,560

*Determined, as described (14), by microneutralization assay in Vero cells. WNV, West Nile virus; CPE, cytopathic effect; NSW, New South Wales; KUN, Kunjin; NY, New York; NT, Northern Territory; mAb, monoclonal antibody.
†Boldface indicates serum samples with >4-fold difference in titer between virus strains.
‡Determined by using a microscope to assess the level of CPE in each well compared with that in control wells.
§Determined by the absence of viral antigen in the cell monolayer of each well when tested with a WNV-reactive mAb in ELISA.
¶Samples from uninfected horses.
#Samples from horses infected with WNV during the 2011 outbreak in New South Wales, Australia.
**Samples from horses infected with WNVKUN in Northern Territory, Australia.
††Samples from horses infected with WNV in the United States.
‡‡This mAb has potent WNV-neutralizing activity (11).

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1These authors contributed equally to the major technical aspects of this research.

2These authors served as joint senior authors.

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