Kinetics of Neutralizing Antibodies in Patients Naturally Infected by H5N1 Virus

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Philippe Buchy1*, Sirenda Vong1, Simon Chu1, Jean-Michel Garcia2, Tran Tinh Hien3,4, Vo Minh Hien3,4, Mey Channa1, Do Quang Ha4, Nguyen Van Vinh Chau4, Cameron Simmons4, Jeremy J. Farrar4, Malik Peiris2,5, Menno D. de Jong4,6

1 Institut Pasteur in Cambodia, Phnom Penh, Cambodia,
2 HKU-Pasteur Research Centre, Hong Kong SAR, China,
3 Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam,
4 Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam,
5 Department of Microbiology, University of Hong Kong, Hong Kong SAR, China,
6 Academic Medical Center, Department of Medical Microbiology, University of Amsterdam, Amsterdam, The Netherlands

Abstract

Background: Little is known about the kinetics of anti-H5 neutralizing antibodies in naturally H5N1-infected patients with severe clinical illness or asymptomatic infection.

Methods: Using H5N1 microneutralisation (MN) and H5-pseudotype particle-based microneutralisation assays (H5pp) we analyzed sera sequentially obtained from 11 severely ill patients diagnosed by RT-PCR (follow-up range 1–139 weeks of disease onset) and 31 asymptomatically infected individuals detected in a sero-epidemiological study after exposure to H5N1 virus (follow-up range: 1–2 month –11 months after exposure).

Results: Of 44 sera from 11 patients with H5N1 disease, 70% tested positive by MN (antibody titre $80) after 2 weeks and 100% were positive by 3 weeks after disease onset. The geometric mean MN titers in severely ill patients were 540 at 1–2 months and 173 at 10–12 months and thus were higher than the titers from asymptomatic individuals (149 at 1–2 months, 62.2 at 10–12 months). Fractional polynomial regression analysis demonstrated that in all severely ill patients, positive titers persisted beyond 2 years of disease onset, while 10 of 23 sera collected 10–11 months after exposure in asymptomatically infected individuals tested negative.

Conclusions: Our results indicate that people with asymptomatic H5N1 infection have lower H5N1 antibody titres compared to those with severe illness and that in many asymptomatically infected patients the antibody titer decreased to levels below the threshold

Seroprevalence of anti-H5 antibody in rural Cambodia, 2007 Philippe Cavailler a,∗, Simon Chua, Sowath Lya, Jean Michel Garciab, Do Quang Hac, Isabelle Bergerid, Leakhann Some, Sovann Lye, Touch Soke, Sirenda Vonga, Philippe Buchya

a Institut Pasteur in Cambodia, Phnom Penh, Cambodia
b HKU-Pasteur Research Center, Hong Kong SAR, People's Republic of China
c Oxford University Clinical Research Unit, Hospital for Tropical Diseases, Ho Chi Minh City, Viet Nam
d World Health Organization, Phnom Penh, Cambodia
e Ministry of Health, Communicable Disease Control Department, Phnom Penh, Cambodia

a r t i c l e i n f o

Article history:

Received 23 September 2009 Received in revised form 21 February 2010 Accepted 26 February 2010
Keywords:
H5N1 virus
Cambodia
Risk factors
Neutralizing antibodies
Seroprevalence
Environmental exposure

a b s t r a c t

Background: Since 2005, eight patients with H5N1 infection were laboratory confirmed in Cambodia. Despite the widespread of highly pathogenic avian influenza H5N1 virus and the intense exposure to poultry, there is growing evidence that H5N1 viruses may not be easily transmitted to human.

Objectives: To evaluate the frequency of H5N1 transmission in rural Cambodia, to identify potential risk factors for H5N1 in humans and to explore the extent of asymptomatic and clinically mild illness among humans.

Study design: A seroepidemiologic survey was conducted, 9 weeks after the recognition that H5N1 infection caused the death of a 13 years old female in April 2007. Blood specimens were collected from 700 participants for H5N1 serological testing. All participants were interviewed with standardized questionnaire to collect information about poultry exposure.

Results: Eighteen (2.6%) of the 700 villagers were tested positive cases for H5N1 antibodies. These 18 individuals were more likely than seronegative participants to report bathing or swimming in the community pond (p = 0.04).

Conclusions: The seroprevalence of H5N1 antibodies was higher than previously reported in the other investigations conducted in Cambodia and Thailand. This finding reinforces the overwhelming evidence that the virus continues to circulate widely in settings where human have high exposure to poultry. Our results, provides additional evidence suggesting that bathing or swimming in the community ponds, remains important potential risk factor for H5N1 infection. Both wild birds and domestic poultry have free access to these ponds which are also used for aquaculture through the dumping of poultry feces for fish feeding.

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Institut Pasteur du Cambodge

Kinetics of Neutralizing Antibodies in Patients Naturally Infected by H5N1 Virus

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