Temporal trends in the discovery of human viruses

Abstract

On average, more than two new species of human virus are reported every year. We constructed the cumulative species discovery curve for human viruses going back to 1901. We fitted a statistical model to these data; the shape of the curve strongly suggests that the process of virus discovery is far from complete. We generated a 95% credible interval for the pool of as yet undiscovered virus species of 38-562. We extrapolated the curve and generated an estimate of 10-40 new species to be discovered by 2020. Although we cannot predict the level of health threat that these new viruses will present, we conclude that novel virus species must be anticipated in public health planning. More systematic virus discovery programmes, covering both humans and potential animal reservoirs of human viruses, should be considered.

Figure 1

The discovery curve for human virus species. Cumulative number of species reported to infect humans (black circles and line). Statistically significant upward breakpoints are shown (vertical lines). Best-fit curve (solid line) and lower and upper 95% posterior prediction intervals (dashed lines) for extrapolation to 2020.

Figure 2

Approximate probability density of variance in simulated data from 1954 to 2006 for the best-fit model. Arrow shows observed value.

Figure 3

Approximate probability density function of parameter p and N generated by MCMC methods (see main text for details).

Figure 4

Accumulation of virus families associated with species discovered after 1954 (black circles and line). Best-fit curve (solid line) and lower and upper 95% posterior prediction intervals (dashed lines) extrapolated to 2020. Fitted parameter values are N=25 (95% credible intervals 24–37) and p=0.056 (0.027–0.089).

Figure 5

Frequency distribution for the number per year of virus families associated with species discovered from 1954 to 2006, generated by reassigning the discovered viruses to families, repeated 10⁶ times. Expected number with 95% credible intervals (bars) and data (black circles).