"Health Security" is a relatively new entrant to the broad concept of national security.  A  fierce debate has raged over whether to expand  the concept from military threats and defense to  energy, environment, drugs, etc.  Richard Ullman proposed that national security be defined as either "an action or sequence of events that

  1. threatens drastically and over a relatively brief span of time to degrade the quality of life for the inhabitants of a state, or

  2. threatens significantly to narrow the range of policy choices available to the government of a state or to private, non-governmental entities (persons, groups, corporations) within the state."

Plagues can have disastrous effects.  When large numbers--a fourth to a half-- die in a society, or are significantly unable to participate in the social and economic life of the community,  state capacity suffers.  Not only is government unable to respond effectively to the challenge, but neighbors/enemies may enter, plunder and conquer.  One only needs to look at recent events in the Congo/Zaire, where armies from 7 states contest over the spoils.      

Here are links to descriptions and analyses of past plagues, which show the damage internally and externally.  This is what we might expect to see in sub-Saharan Africa.  

 

Thucydides on the Plague of Athens

The Pequot Tribe and Plague

Black Death in Florence and Siena

See "Meeting the Global Challenge" by Brookings on security implications.  
Justinian Plague  

Andrew T. Price-Smith, The Health of Nations (MIT Press, 2002), ch. 4.  Dennis Pirages, "Ecological Security: Micro-Threats to Human Well-Being" presented at International Studies Association, 1996.  Laurie Garrett, "The Return of Infectious Disease" Foreign Affairs 75, n 1 (1996), pp. 66-79. 

*Richard Ullman, "Redefining Security," International Security 8, n1  (1983)p. 129,