\documentclass[10pt]{article}
\usepackage{pgf,tikz}
\usetikzlibrary{arrows}
\pagestyle{empty}
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,>=triangle 45,x=1.0cm,y=1.0cm]
\clip(-4.3,1.98) rectangle (9.96,6.3);
\draw [line width=1.2pt] (-0.28,3.88)-- (0.72,3.88);
\draw [line width=1.2pt] (0.72,3.88)-- (0.72,2.88);
\draw [line width=1.2pt] (0.72,2.88)-- (-0.28,2.88);
\draw [line width=1.2pt] (-0.28,3.88)-- (-0.28,2.88);
\draw [line width=1.2pt] (2.72,3.88)-- (3.72,3.88);
\draw [line width=1.2pt] (3.72,3.88)-- (3.72,2.88);
\draw [line width=1.2pt] (3.72,2.88)-- (2.72,2.88);
\draw [line width=1.2pt] (2.72,3.88)-- (2.72,2.88);
\draw [line width=1.2pt] (5.72,3.88)-- (6.72,3.88);
\draw [line width=1.2pt] (6.72,3.88)-- (6.72,2.88);
\draw [line width=1.2pt] (6.72,2.88)-- (5.72,2.88);
\draw [line width=1.2pt] (5.72,3.88)-- (5.72,2.88);
\draw [->,line width=1.2pt] (-2.8,3.34) -- (-0.28,3.34);
\draw [->,line width=1.2pt] (0.72,3.36) -- (1.88,3.34);
\draw [line width=1.2pt] (1.88,3.34)-- (2.72,3.34);
\draw [->,line width=1.2pt] (3.72,3.36) -- (4.86,3.36);
\draw [line width=1.2pt] (4.86,3.36)-- (5.72,3.38);
\draw [->,line width=1.2pt] (8.72,3.34) -- (6.72,3.34);
\draw [->,line width=1.2pt] (6.2,3.88) -- (6.2,5.2);
\draw [->,line width=1.2pt] (3.2,3.88) -- (3.18,5.3);
\draw [->,line width=1.2pt] (0.2,3.88) -- (0.18,5.32);
\draw (-2.62,4.2) node[anchor=north west] {$$ \mu (1 - \nu )N $$};
\draw (1.36,4.24) node[anchor=north west] {$$ \beta SI $$};
\draw (-0.06,6.08) node[anchor=north west] {$$ \mu S $$};
\draw (2.9,6.06) node[anchor=north west] {$$ \mu I $$};
\draw (5.84,5.96) node[anchor=north west] {$$ \mu R $$};
\draw (7.32,4.18) node[anchor=north west] {$$ \mu \nu N $$};
\draw (4.32,4.22) node[anchor=north west] {$$ \gamma I $$};
\draw (0.06,3.92) node[anchor=north west] {$$ S $$};
\draw (3.06,3.94) node[anchor=north west] {$$ I $$};
\draw (6.02,3.96) node[anchor=north west] {$$ R $$};
\end{tikzpicture}
\end{document}