Table 1.

Transmission possibilities.

Susceptible	Infected	Transmission term
$S_n$	$I_n$	${\displaystyle \frac{\beta S_n{I}_n}{N}}$
$S_n$	$I_m$	${\displaystyle \frac{r\beta S_n{I}_m}{N}}$
$S_m$	$I_n$	${\displaystyle \frac{r\beta S_m{I}_n}{N}}$
$S_m$	$I_m$	${\displaystyle \frac{r^2\beta S_m{I}_m}{N}}$