This is an antiviral drug-mechanism module structured as a biological pathway, not a specific disease. Its nodes are successive biological steps of late virion morphogenesis and egress (progeny-virion assembly -> budding at the host membrane -> neuraminidase-mediated release -> suppression of release/spread), with an adaptive resistance branch; the drug classes that act on each step are described in the node text rather than modelled as separate nodes. Disorder entries reference individual nodes via conforms_to (e.g., "viral_assembly_release_inhibition#Neuraminidase-Mediated Release of Progeny Virions"), and their assembly/release-targeting treatments point at the inhibited node via target_mechanisms (the neuraminidase-release node for the neuraminidase inhibitors; the assembly node for the HCV NS5A inhibitors), analogous to how polymerase-targeting treatments link to "viral_polymerase_inhibition#Nucleotide Selection and Catalytic Incorporation at the Polymerase Active Site" and cell-wall-active antibiotic treatments link to "bacterial_cell_wall_synthesis_inhibition#Peptidoglycan Cross-Linking by Penicillin-Binding Proteins". Key conformance / treatment target: "Neuraminidase-Mediated Release of Progeny Virions" — the influenza-neuraminidase sialidase step that frees budded virions and is the target of the neuraminidase inhibitors. The resistance node captures the gating knowledge that distinguishes "an assembly/release inhibitor is used" from real drug selection — target-site substitutions (NA H275Y, NS5A RASs) that escape these agents. See projects/ANTIVIRAL.md.
Assembly of Progeny Virions
trigger
The infectious cycle is completed only when newly synthesised viral components are collected and assembled into progeny particles at a dedicated membrane assembly site. Because complete virions are not found pre-formed inside the cell, this assembly step is obligatory for producing infectious particles and is the committed start of the egress cascade. In hepatitis C virus the nonstructural phosphoprotein NS5A organises the membranous replication/assembly complex ("replication factory") and is essential for virion assembly; the NS5A inhibitors (the "-asvir" class — ledipasvir, velpatasvir, daclatasvir) act at exactly this assembly-organising step, disrupting replication-complex formation, and are essential components of curative DAA combinations.
Downstream
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Budding of Virions at the Host Membrane
Once components are assembled at the membrane assembly site, nascent particles bud outward from the host plasma membrane.
Budding of Virions at the Host Membrane
effector
After assembly, nascent virions form and bud outward from the host plasma membrane. For enveloped viruses such as influenza this proceeds through bud initiation, bud growth, and bud scission/release, with all virion components brought to the apical membrane budding site and matrix and envelope proteins (M1, M2, and neuraminidase) driving bud release. Budding produces particles that are still tethered to the cell surface and to each other, setting up the requirement for the neuraminidase-mediated detachment step that follows.
Downstream
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Neuraminidase-Mediated Release of Progeny Virions
Budded influenza virions remain tethered by sialic acid and require neuraminidase to cleave it and free them for spread.
Suppression of Progeny Virion Release and Spread
consequence
When the assembly/release cascade is pharmacologically engaged, mature progeny virions can no longer be liberated and disseminated. For influenza, neuraminidase inhibitors leave newly budded virions aggregated and tethered to sialic acid on the host-cell surface and on each other, so the yield of released infectious progeny collapses and cell-to-cell spread is arrested; for HCV, NS5A inhibitors block replication-complex formation and virion assembly so that infectious particle production fails. This is the antiviral consequence of engaging the upstream release/assembly target — analogous to chain termination for polymerase inhibitors. Because it acts at the spread step rather than at initial entry, the clinical benefit of neuraminidase inhibitors is greatest when treatment begins early, before peak viral replication.
Assembly/Release-Inhibitor Resistance
adaptive escape
Target-site substitutions in the assembly/release machinery escape these inhibitors. In influenza A(H1N1), the neuraminidase H275Y substitution confers high-level oseltamivir resistance and can spread in circulating viruses, while additional NA changes (e.g. R294K, the I223R/H275Y double mutant) reduce inhibition across the neuraminidase-inhibitor class. In hepatitis C, NS5A resistance-associated substitutions (RASs) pre-exist in the quasispecies and reduce the potency of NS5A inhibitors at the upstream assembly step, which is why NS5A agents are used within multi-target DAA combinations rather than as monotherapy. This adaptive branch explains why an assembly/release inhibitor can fail against a specific variant and why surveillance, susceptibility testing, and combination regimens gate the real use of these agents. Conforming entries can attach a treatment's failure mode or a combination rationale to this node.