Communicable diseases

Communicable diseases are those that are transmissible from one person, or animal, to another. The disease may be spread directly, via another species (vector) or via the environment. Illness will arise when the infectious agent invades the host, or sometimes as a result of toxins produced by bacteria in food. The spread of disease through a population is determined by environmental and social conditions which favour the infectious agent, and the relative immunity of the population. An outbreak of infection could endanger the operation and safety of the ship. An understanding of the disease and the measures necessary for its containment and management is therefore important.

In reality it is often very difficult to make an accurate diagnosis of an infectious disease without laboratory investigations. It may be possible if there are very specific features such as a rash (varicella) or cluster of suggestive features (regular fever, enlarged spleen and history of mosquito bites in an endemic area). Because of the difficulty in making an accurate diagnosis on board ship you may have to give a variety of treatments each directed at different infectious agents.
 
Onset
 
Almost all communicable diseases begin with the patient feeling unwell and perhaps a rise in temperature. This period may be very short, lasting only a few hours (meningococcal sepsis), or more prolonged (hepatitis). In some diseases the onset is mild and there is not much general disturbance of health, whereas in others it is severe and prostrating. During the onset it is rarely possible to make a diagnosis.
 
The rash
 
The diagnosis of some communicable diseases is made easier by the presence of a characteristic rash. In certain diseases (e.g. scarlet fever) the rash is spread evenly over the body, in others it is limited to definite areas. When examining an individual suspected to be suffering from a communicable disease, it is of great importance to strip him completely in order to get a full picture of any rash and its distribution.