Virus Burst Size Calculator

Calculate virus burst size, replication cycle time, and phage/virus production from one-step growth curve.

Virus titer before lysis (PFU/mL) (PFU/mL)

Virus titer after lysis (PFU/mL) (PFU/mL)

Number of infected cells/mL (cells/mL)

Latent period (min) (min)

Rise period (min) (min)

Please check your inputs and try again.

Reading a One-Step Growth Curve

The experiment synchronises infection so a single replication cycle can be observed. Three phases follow, and each parameter comes from a different one.

Phase	What is happening	Parameter obtained
Latent period	Eclipse and assembly — no release	Time to first rise
Rise period	Progressive lysis across the population	Slope
Plateau	All infected cells lysed	Burst size from final titre

Burst size = (final titre − initial titre) / infected cells

The latent period contains an eclipse phase during which no infectious virus exists even inside the cell — the genome has been released and replication started, but no complete virions have assembled. Artificial lysis during eclipse yields nothing.

Virus	Burst size	Latent period
Phage T4	100–200	~25 min
Phage lambda	~100	~50 min
Poliovirus	10,000–100,000	6–8 hr
Influenza	1,000–10,000	Budding, not lysis

The Latent Period Trade-Off

Lysing early releases progeny sooner but with fewer virions per cell; waiting produces more but delays release and risks the host dying first. Optimal latent period depends on host density — when hosts are abundant, short latent periods win the race; when scarce, maximising yield per cell matters more.

This is a genuine evolutionary optimisation, and phage strains isolated from different environments show latent periods consistent with it.

Note that budding viruses such as influenza and HIV release progeny continuously rather than in a burst, so "burst size" is a total yield per cell rather than a synchronous event. MOI also matters: at high MOI, multiple infections of one cell inflate the apparent burst size unless corrected.

Worked Examples

Example 1: Phage T4: pre=1e5, post=1.5e7, cells=1e5

Burst=150 PFU/cell

Result: Classic burst size for T4 phage

One-step growth experiment (Ellis & Delbrück 1939)

Example 2: SARS-CoV-2 in VeroE6: 1000 PFU/cell

High burst size for coronavirus

Result: Each infected cell produces ~1000 virions

Many are non-infectious (defective)—PFU underestimates total particles

Example 3: The latent period trade-off

High versus low host density

Result: Short versus long latent period favoured

When hosts are abundant, releasing sooner wins the race for uninfected cells. When scarce, maximising yield per cell matters more.

Example 4: Why eclipse matters experimentally

Lysing cells 5 minutes after infection

Result: No infectious virus recovered

The genome has entered and replication begun, but no complete virions have assembled yet. This defines the eclipse phase.

Common Mistakes

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Measuring before the plateau

Burst size requires all infected cells to have lysed. Sampling during the rise period underestimates it.

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Ignoring the eclipse phase

No infectious virus exists inside the cell early in the latent period. Artificial lysis then yields nothing, which is expected rather than a failed experiment.

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Using high MOI

Multiple infections of the same cell inflate apparent burst size. Low MOI ensures roughly one infection per cell.

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Applying burst size to budding viruses

Influenza and HIV release progeny continuously rather than by lysis. Total yield per cell is the meaningful quantity instead.

Frequently Asked Questions

One-step growth curve method?

Add phage to bacteria at low MOI (~0.1). At t=0: add CHCl3 to lyse immediately (extracellular virus = free phage). Latent period: no increase in PFU. Rise period: burst. Latent period timing reveals intracellular events: phage DNA injection, replication, head/tail assembly.

Burst size ecological implications?

Large burst size: rapid epidemic spread but also rapid host population crash (boom-bust). Small burst size: more persistent infection. HIV: chronic with constant low-level burst. Some temperate phages (lysogeny): integrate into host genome, burst = 0 until induced.

What is the eclipse phase?

The early part of the latent period when no infectious virus exists even inside the cell, because genome replication has begun but assembly has not.

Why use a low MOI?

So that most cells receive a single virion. Multiple infections of one cell inflate the apparent burst size.

What determines the optimal latent period?

Host density. Abundant hosts favour early release; scarce hosts favour longer latency and higher yield per cell.

Does burst size apply to budding viruses?

Not in the same sense. Influenza and HIV release progeny continuously, so total yield per cell replaces the idea of a synchronous burst.