Erin M. Sorrell

Airborne Transmission of Influenza A/H5N1 Virus Between Ferrets

Avian flu can acquire the capacity for airborne transmission between mammals without recombination in an intermediate host. Highly pathogenic avian influenza A/H5N1 virus can cause morbidity and mortality in humans but thus far has not acquired the ability to be transmitted by aerosol or respiratory droplet (“airborne transmission”) between humans. To address the concern that the virus could acquire this ability under natural conditions, we genetically modified A/H5N1 virus by site-directed mutagenesis and subsequent serial passage in ferrets. The genetically modified A/H5N1 virus acquired mutations during passage in ferrets, ultimately becoming airborne transmissible in ferrets. None of the recipient ferrets died after airborne infection with the mutant A/H5N1 viruses. Four amino acid substitutions in the host receptor-binding protein hemagglutinin, and one in the polymerase complex protein basic polymerase 2, were consistently present in airborne-transmitted viruses. The transmissible viruses were sensitive to the antiviral drug oseltamivir and reacted well with antisera raised against H5 influenza vaccine strains. Thus, avian A/H5N1 influenza viruses can acquire the capacity for airborne transmission between mammals without recombination in an intermediate host and therefore constitute a risk for human pandemic influenza.

Replication and transmission of H9N2 influenza viruses in ferrets: evaluation of pandemic potential.

H9N2 avian influenza A viruses are endemic in poultry of many Eurasian countries and have caused repeated human infections in Asia since 1998. To evaluate the potential threat of H9N2 viruses to humans, we investigated the replication and transmission efficiency of H9N2 viruses in the ferret model. Five wild-type (WT) H9N2 viruses, isolated from different avian species from 1988 through 2003, were tested in vivo and found to replicate in ferrets. However these viruses achieved mild peak viral titers in nasal washes when compared to those observed with a human H3N2 virus. Two of these H9N2 viruses transmitted to direct contact ferrets, however no aerosol transmission was detected in the virus displaying the most efficient direct contact transmission. A leucine (Leu) residue at amino acid position 226 in the hemagglutinin (HA) receptor-binding site (RBS), responsible for human virus-like receptor specificity, was found to be important for the transmission of the H9N2 viruses in ferrets. In addition, an H9N2 avian-human reassortant virus, which contains the surface glycoprotein genes from an H9N2 virus and the six internal genes of a human H3N2 virus, showed enhanced replication and efficient transmission to direct contacts. Although no aerosol transmission was observed, the virus replicated in multiple respiratory tissues and induced clinical signs similar to those observed with the parental human H3N2 virus. Our results suggest that the establishment and prevalence of H9N2 viruses in poultry pose a significant threat for humans.

Minimal molecular constraints for respiratory droplet transmission of an avian–human H9N2 influenza A virus

Pandemic influenza requires interspecies transmission of an influenza virus with a novel hemagglutinin (HA) subtytpe that can adapt to its new host through either reassortment or point mutations and transmit by aerosolized respiratory droplets. Two previous pandemics of 1957 and 1968 resulted from the reassortment of low pathogenic avian viruses and human subtypes of that period; however, conditions leading to a pandemic virus are still poorly understood. Given the endemic situation of avian H9N2 influenza with human-like receptor specificity in Eurasia and its occasional transmission to humans and pigs, we wanted to determine whether an avian–human H9N2 reassortant could gain respiratory transmission in a mammalian animal model, the ferret. Here we show that following adaptation in the ferret, a reassortant virus carrying the surface proteins of an avian H9N2 in a human H3N2 backbone can transmit efficiently via respiratory droplets, creating a clinical infection similar to human influenza infections. Minimal changes at the protein level were found in this virus capable of respiratory droplet transmission. A reassortant virus expressing only the HA and neuraminidase (NA) of the ferret-adapted virus was able to account for the transmissibility, suggesting that currently circulating avian H9N2 viruses require little adaptation in mammals following acquisition of all human virus internal genes through reassortment. Hemagglutinin inhibition (HI) analysis showed changes in the antigenic profile of the virus, which carries profound implications for vaccine seed stock preparation against avian H9N2 influenza. This report illustrates that aerosolized respiratory transmission is not exclusive to current human H1, H2, and H3 influenza subtypes.

Compatibility of H9N2 avian influenza surface genes and 2009 pandemic H1N1 internal genes for transmission in the ferret model

In 2009, a novel H1N1 influenza (pH1N1) virus caused the first influenza pandemic in 40 y. The virus was identified as a triple reassortant between avian, swine, and human influenza viruses, highlighting the importance of reassortment in the generation of viruses with pandemic potential. Previously, we showed that a reassortant virus composed of wild-type avian H9N2 surface genes in a seasonal human H3N2 backbone could gain efficient respiratory droplet transmission in the ferret model. Here we determine the ability of the H9N2 surface genes in the context of the internal genes of a pH1N1 virus to efficiently transmit via respiratory droplets in ferrets. We generated reassorted viruses carrying the HA gene alone or in combination with the NA gene of a prototypical H9N2 virus in the background of a pH1N1 virus. Four reassortant viruses were generated, with three of them showing efficient respiratory droplet transmission. Differences in replication efficiency were observed for these viruses; however, the results clearly indicate that H9N2 avian influenza viruses and pH1N1 viruses, both of which have occasionally infected pigs, have the potential to reassort and generate novel viruses with respiratory transmission potential in mammals.

A 27-Amino-Acid Deletion in the Neuraminidase Stalk Supports Replication of an Avian H2N2 Influenza A Virus in the Respiratory Tract of Chickens

ABSTRACT The events and mechanisms that lead to interspecies transmission of, and host adaptation to, influenza A virus are unknown; however, both surface and internal proteins have been implicated. Our previous report highlighted the role that Japanese quail play as an intermediate host, expanding the host range of a mallard H2N2 virus, A/mallard/Potsdam/178-4/83 (H2N2), through viral adaptation. This quail-adapted virus supported transmission in quail and increased its host range to replicate and be transmitted efficiently in chickens. Here we report that of the six amino acid changes in the quail-adapted virus, a single change in the hemagglutinin (HA) was crucial for transmission in quail, while the changes in the polymerase genes favored replication at lower temperatures than those for the wild-type mallard virus. Reverse genetic analysis indicated that all adaptive mutations were necessary for transmission in chickens, further implicating quail in extending this virus to terrestrial poultry. Adaptation of the quail-adapted virus in chickens resulted in the alteration of viral tropism from intestinal shedding to shedding and transmission via the respiratory tract. Sequence analysis indicated that this chicken-adapted virus maintained all quail-adaptive mutations, as well as an additional change in the HA and, most notably, a 27-amino-acid deletion in the stalk region of neuraminidase (NA), a genotypic marker of influenza virus adaptation to chickens. This stalk deletion was shown to be responsible for the change in virus tropism from the intestine to the respiratory tract.

Transmission of influenza A/H5N1 viruses in mammals

Highly pathogenic avian H5N1 influenza A viruses occasionally infect humans and cause severe respiratory disease and fatalities. Currently, these viruses are not efficiently transmitted from person to person, although limited human-to-human transmission may have occurred. Nevertheless, further adaptation of avian H5N1 influenza A viruses to humans and/or reassortment with human influenza A viruses may result in aerosol transmissible viruses with pandemic potential. Although the full range of factors that modulate the transmission and replication of influenza A viruses in humans are not yet known, we are beginning to understand some of the molecular changes that may allow H5N1 influenza A viruses to transmit via aerosols or respiratory droplets among mammals. A better understanding of the biological basis and genetic determinants that confer transmissibility to H5N1 influenza A viruses in mammals is important to enhance our pandemic preparedness.

Avian influenza: an omnipresent pandemic threat.

Background: Humans have faced 3 major influenza pandemics in the 20th century. In recent years, it has become evident that domestic poultry play an important role in the generation of novel influenza strains with the capacity to cross the species barrier and infect and kill humans at an alarming rate. There is particular concern that avian influenza viruses of the H5N1 subtype could cause a pandemic. Methods: A better understanding of the genetic factors that lead to interspecies transmission is essential to prevent the emergence of influenza pandemics. In addition, the stockpiling of antiviral drugs and development of vaccines against potentially pandemic viruses must be considered under the umbrella of pandemic plans. Results: The world is ill-prepared to face an influenza pandemic. Only a handful of countries have developed influenza pandemic plans, and even fewer are developing vaccines or stockpiling antiinfluenza drugs to ameliorate the impact of a potential pandemic. Currently the major undertaking in several at risk nations is to implement effective control measures to stop the spread of the virus at its source, that is, avian species. These measures include the culling of domestic poultry to contain the virus, a practice that could eventually bring these countries to a financial and social breaking point. Conclusions: Avian influenza disease is preventable in humans and birds with the concerted effort of governments and poultry producers, large and small, to improve biosecurity and education programs. Pandemic plans can reduce the impact of the pandemic; however, preventing avian influenza in poultry can avert a pandemic altogether.

Mapping of Networks to Detect Priority Zoonoses in Jordan

Early detection of emerging disease events is a priority focus area for cooperative bioengagement programs. Communication and coordination among national disease surveillance and response networks are essential for timely detection and control of a public health event. Although systematic information sharing between the human and animal health sectors can help stakeholders detect and respond to zoonotic diseases rapidly, resource constraints, and other barriers often prevent efficient cross-sector reporting. The purpose of this research project was to map the laboratory and surveillance networks currently in place for detecting and reporting priority zoonotic diseases in Jordan in order to identify the nodes of communication, coordination, and decision-making where health and veterinary sectors intersect, and to identify priorities and gaps that limit information sharing for action. We selected three zoonotic diseases as case studies: highly pathogenic avian influenza (HPAI) H5N1, rabies, and brucellosis. Through meetings with government agencies and health officials, and desk research, we mapped each system from the index case through response – including both surveillance and laboratory networks, highlighting both areas of strength and those that would benefit from capacity-building resources. Our major findings indicate informal communication exists across sectors; in the event of emergence of one of the priority zoonoses studied, there is effective coordination across the Ministry of Health and Ministry of Agriculture. However, routine formal coordination is lacking. Overall, there is a strong desire and commitment for multi-sectoral coordination in detection and response to zoonoses across public health and veterinary sectors. Our analysis indicates that the networks developed in response to HPAI can and should be leveraged to develop a comprehensive laboratory and surveillance One Health network.

Linking funds to actions for global health emergencies

The International Health Regulations could help align and trigger World Bank and World Health Organization efforts The failings of the international communitys response to the Ebola virus disease outbreak in West Africa underscore the need for new mechanisms for governance and mobilization of resources for timely, coordinated responses to public health threats (1). Creating a global finance mechanism, ideally tied to existing global health frameworks, is a first step. The World Bank recently announced it would create a Pandemic Emergency Facility (PEF). The next necessary element is a trigger to release those funds to support rapid and effective responses during early phases of a public health event. With the World Health Assembly convening soon, we suggest how the World Health Organizations (WHOs) International Health Regulations (IHR) present such an initiator.

Implementation of the International Health Regulations (2005) Through Cooperative Bioengagement

Cooperative bioengagement efforts, as practiced by U.S. government-funded entities, such as the Defense Threat Reduction Agency’s Cooperative Biological Engagement Program, the State Department’s Biosecurity Engagement Program, and parallel programs in other countries, exist at the nexus between public health and security. These programs have an explicit emphasis on developing projects that address the priorities of the partner country as well as the donor. While the objectives of cooperative bioengagement programs focus on reducing the potential for accidental or intentional misuse and/or release of dangerous biological agents, many partner countries are interested in bioengagement as a means to improve basic public health capacities. This article examines the extent to which cooperative bioengagement projects address public health capacity building under the revised International Health Regulations and alignment with the Global Health Security Agenda action packages.