Antivirals in the management of an influenza pandemic

Antiviral prophylaxis and isolation for the control of pandemic influenza

Before effective vaccines become available, antiviral drugs are considered as the major control strategies for a pandemic influenza. However, perhaps such control strategies can be severely hindered by the low-efficacy of antiviral drugs. For this reason, using antiviral drugs and an isolation strategy is included in our study. A compartmental model that allows for imported exposed individuals and asymptomatic cases is used to evaluate the effectiveness of control strategies via antiviral prophylaxis and isolation. Simulations show that isolation strategy plays a prominent role in containing transmission when antiviral drugs are not effective enough. Moreover, relatively few infected individuals need to be isolated per day. Because the accurate calculations of the needed numbers of antiviral drugs and the isolated infected are not easily available, we give two simple expressions approximating these numbers. We also derive an estimation for the total cost of these intervention strategies. These estimations obtained by a simple method provide a useful reference for the management department about the epidemic preparedness plans.

Ching-fang-pai-tu-san inhibits the release of influenza virus

ETHNOPHARMACOLOGICAL RELEVANCE

Ching-fang-pai-tu-san (CFPTS) is a Chinese herbal decoction that is used as a cure for the common cold, fever, headache, and poor circulation. However, no previous studies have investigated the mode of action of CFPTS against influenza virus infections. To investigate the antiviral mechanism of CFPTS, we examined viral entry, transcription, translation, viral glycoprotein hemagglutinin (HA) transport, and budding of the influenza virus.

MATERIALS AND METHODS

The antiviral activity of nontoxic concentrations of CFPTS against influenza virus A/WSN/33 was examined by assaying (neutralization assay) its inhibition of the virus-induced cytopathic effects. The mode of CFPTS action was first examined with a time-of-addition assay of synchronized infections, followed by monitoring HA transport by immunofluorescence microscopy. Viral endocytosis was evaluated with attachment and penetration assays. The inhibition of viral replication was measured by quantitative real-time PCR, immunoblotting, and immunofluorescence microscopy. We also performed assays related to the inhibition of viral entry, such as neuraminidase activity and hemagglutinin activity assays.

RESULTS

Based on the inhibition of the virus-induced cytopathic effect in Madin-Darby canine kidney cells, the EC(50) of CFPTS was about 1.44 ± 0.22 mg/mL against influenza virus A/WSN/33. CFPTS displayed a broad spectrum of inhibitory activities against different strains of influenza A virus, as well as some enteroviruses. However, this extract proved less effective against clinical oseltamivir-resistant strains and influenza B viruses. CFPTS did not suppress viral RNA or protein synthesis. According to a time-of-addition assay, the antiviral mechanism of CFPTS may involve viral budding or intracellular viral glycoprotein transport. A plaque reduction assay showed that CFPTS reduced both the plaque size and plaque quantity. The intracellular transport of viral glycoprotein hemagglutinin was blocked by CFPTS by immunofluorescence microscopic analysis. Thus, it is possible that the antiviral mechanism of CFPTS might inhibit the assembly of progeny virions and/or their subsequent release.

CONCLUSIONS

Our results give scientific support to the use of CFPTS in the treatment of influenza virus infections. CFPTS has potential utility in the management of seasonal pandemics of influenza virus infections, like other clinically available drugs.

Can antiviral drugs contain pandemic influenza transmission?

Antiviral drugs dispensed during the 2009 influenza pandemic generally failed to contain transmission. This poses the question of whether preparedness for a future pandemic should include plans to use antiviral drugs to mitigate transmission.

Simulations using a standard transmission model that allows for infected arrivals and delayed vaccination show that attempts to contain transmission require relatively few antiviral doses. In contrast, persistent use of antiviral drugs when the reproduction number remains above 1 use very many doses and are unlikely to reduce the eventual attack rate appreciably unless the stockpile is very large. A second model, in which the community has a household structure, shows that the effectiveness of a strategy of dispensing antiviral drugs to infected households decreases rapidly with time delays in dispensing the antivirals. Using characteristics of past pandemics it is estimated that at least 80% of primary household cases must present upon show of symptoms to have a chance of containing transmission by dispensing antiviral drugs to households. To determine data needs, household outbreaks were simulated with 50% receiving antiviral drugs early and 50% receiving antiviral drugs late. A test to compare the size of household outbreaks indicates that at least 100–200 household outbreaks need to be monitored to find evidence that antiviral drugs can mitigate transmission of the newly emerged virus.

Use of antiviral drugs in an early attempt to contain transmission should be part of preparedness plans for a future influenza pandemic. Data on the incidence of the first 350 cases and the eventual attack rates of the first 200 hundred household outbreaks should be used to estimate the initial reproduction number R and the effectiveness of antiviral drugs to mitigate transmission. Use of antiviral drugs to mitigate general transmission should cease if these estimates indicate that containment of transmission is unlikely.

Therapy of experimental influenza virus infection with pyrrolidine dithiocarbamate

The search for new antiviral strategies to treat influenza A virus (IAV) infections is one major international health care activity. Hereby, the IAV-caused misuse of cellular nuclear factor kappa B (NF-κB) signaling pathways in infected cells represents one target for antiviral therapy. In the present study, pyrrolidine dithiocarbamate (PDTC), which is known as an antioxidant and as an inhibitor of IAV-induced NF-κB activation, was studied in vivo. After the antiviral activity of PDTC was confirmed in MDCK cells, mice-infected with the mouse-adapted strain of IAV A/PR/8/34 (H1N1)-were treated intraperitoneally simultaneously with PDTC (75, 150, 200 mg/kg body weight). The influence of PDTC administrations was evaluated on viral replication and inflammatory reactions in lung tissue up to 14 days postinfection (p. i.). This therapy increased survival up to 80% and reduced IAV-caused weight loss and viral replication in lung tissue in a dose-dependent manner. Protective effects were less pronounced, if the therapy started later on during an ongoing IAV infection. In addition, simultaneous PDTC treatment also limited IAV-caused infiltration of immune cells as well as local interferon-γ expression in lung tissue. These results imply that PDTC decreases IAV-caused disease in mice significantly. Therefore, the development of drugs like PDTC that interfere with NF-κB signaling may represent a modern focus of anti-IAV therapy.

Decision making with regard to antiviral intervention during an influenza pandemic

BACKGROUND

Antiviral coverage is defined by the proportion of the population that takes antiviral prophylaxis or treatment. High coverage of an antiviral drug has epidemiological and evolutionary repercussions. Antivirals select for drug resistance within the population, and individuals may experience adverse effects. To determine optimal antiviral coverage in the context of an influenza outbreak, we compared 2 perspectives: 1) the individual level (the Nash perspective), and 2) the population level (utilitarian perspective).

METHODS

We developed an epidemiological game-theoretic model of an influenza pandemic. The data sources were published literature and a national survey. The target population was the US population. The time horizon was 6 months. The perspective was individuals and the population overall. The interventions were antiviral prophylaxis and treatment. The outcome measures were the optimal coverage of antivirals in an influenza pandemic.

RESULTS

At current antiviral pricing, the optimal Nash strategy is 0% coverage for prophylaxis and 30% coverage for treatment, whereas the optimal utilitarian strategy is 19% coverage for prophylaxis and 100% coverage for treatment. Subsidizing prophylaxis by $440 and treatment by $85 would bring the Nash and utilitarian strategies into alignment. For both prophylaxis and treatment, the optimal antiviral coverage decreases as pricing of antivirals increases. Our study does not incorporate the possibility of an effective vaccine and lacks probabilistic sensitivity analysis. Our survey also does not completely represent the US population. Because our model assumes a homogeneous population and homogeneous antiviral pricing, it does not incorporate heterogeneity of preference.

CONCLUSIONS

The optimal antiviral coverage from the population perspective and individual perspectives differs widely for both prophylaxis and treatment strategies. Optimal population and individual strategies for prophylaxis and treatment might be aligned through subsidization.

An influenza outbreak in a regional residential facility

Influenza is a highly contagious infection with the potential for outbreaks in residential facilities despite seemingly adequate vaccination levels among residents. The management of an influenza A outbreak in a residential facility for cognitively impaired residents of an Australian regional health service is described. Twenty-five of the residents of a 60-bed standalone facility were affected, with one fatality resulting. As virological confirmation of the outbreak was received late on a Friday, the initiation of antiviral treatment and prophylaxis occurred out of hours. The unanticipated consequences of this out-of-hours management are discussed. The management of an influenza outbreak in a dementiaspecific residential facility requires a specific infection control response which anticipates the ethical issues relating to the care of the cognitively impaired.

Therapeutic targets for influenza – perspectives in drug development

Since new and dangerous influenza virus strains, such as H5N1 “avian flu” and more recently the swine-origin H1N1 “swine flu”, are constantly evolving, the need for effective anti-influenza drugs is pressing. It is becoming clear that the emergence of drug-resistant viruses will be a major potential problem in future efforts to control influenza virus infection. Moreover, development of vaccines against new influenza strains takes several months, and their production capacity is limited. Thus, new classes of anti-influenza drugs are highly sought after. This review focuses mainly on novel strategies, including targeting viral entry into host cells, inhibition of viral transcription and genome replication, and targeting of the NS1 influenza protein. Another approach involves viral RNA silencing by siRNAs or by antisense oligonucleotides. Inhibitors of viral neuraminidase have been the most successful approach in influenza virus breakdown to date. Viral maturation can also be blocked by inhibition of hemagglutinin-processing cellular proteinases. Compounds modifying the host cell immune response have also been reported. Design of specific compounds universally active against all viral variants with a reduced potential for the emergence of drug-resistant mutants is the main challenge in anti-influenza drug development, and the goals in this field are discussed here. A review with 140 references.

X-ray structures of NS1 effector domain mutants

The influenza A virus nonstructural protein NS1 is a multifunctional dimeric protein that acts as a potent inhibitor of the host cellular antiviral state. The C-terminal effector domain of NS1 binds host proteins, including CPSF30, and is a target for the development of new antiviral drugs. Here we present crystallographic structures of two mutant effector domains, W187Y and W187A, of influenza A/Udorn/72 virus. Unlike wild-type, the mutants behave exclusively as monomers in solution based on gel filtration data and light scattering. The W187Y mutant is able to bind CPSF30 with a binding affinity close to the wild-type protein; that is, it retains a receptor site for aromatic ligands nearly identical to the wild-type. Therefore, this monomeric mutant protein could serve as a drug target for a high throughput inhibitor screening assays, since its binding pocket is unoccupied in solution and potentially more accessible to small molecule ligands.

How would Australian hospital staff react to an avian influenza admission, or an influenza pandemic?

Objective:  To estimate the expected staff absentee rates and work attitudes in an Australian tertiary hospital workforce in two hypothetical scenarios: (i) a single admission of avian influenza; and (ii) multiple admissions of human pandemic influenza.

Methods:  A survey conducted at hospital staff meetings between May and August 2006.

Results:  Out of 570 questionnaires distributed, 560 were completed. For scenario one, 72 (13%) indicated that they would not attend work, and an additional 136 (25%) would only work provided that immunizations and/or antiviral medications were immediately available, so that up to 208 (38%) would not attend work. For scenario two, 196 (36%) would not attend work, and an additional 95 (17%) would work only if immunizations and/or antiviral medications were immediately available, so that up to 291 (53%) staff would not attend work. Staff whose work required them to be in the ED (odds ratios 2.2 and 1.6 for each scenario respectively) or on acute medical wards (odds ratios 2.2 and 2.0 respectively) were more likely to work.

Conclusion:  High absenteeism among hospital staff should be anticipated if patients are admitted with either avian or pandemic influenza, particularly if specific antiviral preventative measures are not immediately available. Measures to maximize the safety of staff and their families would be important incentives to attend work. Education on realistic level of risk from avian and pandemic influenza, as well as the effectiveness of basic infection control procedures and personal protective equipment, would be useful in improving willingness to work.

Estimating antiviral effectiveness against pandemic influenza using household data

Current estimates of antiviral effectiveness for influenza are based on the existing strains of the virus. Should a pandemic strain emerge, strain-specific estimates will be required as early as possible to ensure that antiviral stockpiles are used optimally and to compare the benefits of using antivirals as prophylaxis or to treat cases. We present a method to measure antiviral effectiveness using early pandemic data on household outbreak sizes, including households that are provided with antivirals for prophylaxis and those provided with antivirals for treatment only. We can assess whether antiviral drugs have a significant impact on susceptibility or on infectivity with the data from approximately 200 to 500 households with a primary case. Fewer households will suffice if the data can be collected before case numbers become high, and estimates are more precise if the study includes data from prophylaxed households and households where no antivirals are provided. Rates of asymptomatic infection and the level of transmissibility of the virus do not affect the accuracy of these estimates greatly, but the pattern of infectivity in the individual strongly influences the estimate of the effect of antivirals on infectivity. An accurate characterization of the infectiousness profile--informed by strain-specific data--is essential for measuring antiviral effectiveness.

Neuraminidase inhibitor resistance in influenza viruses

Zanamivir and oseltamivir, the currently marketed influenza virus neuraminidase inhibitors (NAIs), are prescribed for the treatment and prophylaxis of influenza and are being stockpiled for pandemic influenza. Oseltamivir resistance has been reported in up to 2% of patients in clinical trials of oseltamivir and in up to 18% of treated children. There are also reports in at least three patients treated with oseltamivir for influenza A (H5N1) infections. At this stage, there are no reports of resistance occurring to zanamivir in immunocompetent patients. Zanamivir and oseltamivir bind differently at the neuraminidase catalytic site and this contributes to different drug resistance profiles. The magnitude and duration of NAI concentrations at the site of infection are also expected to be important factors and are determined by route and timing of drug administration, dose, and pharmacokinetic differences between patients. In addition, the type, strain, and virulence of the influenza strain and the nature of the immune response all appear to play a role in determining the likelihood of drug resistance arising. The clinical significance of a particular NAI-resistant isolate from a patient is often not clear but virus viability and transmissibility are clearly important characteristics. Early initiation of NAI treatment in suspected cases of influenza is important for maximizing efficacy and minimizing the risk of drug resistance. Higher NAI doses and longer periods of treatment may be required for patients with influenza A (H5N1) infections but further work is needed in this area.