The  epidemic  potential  is  serious  in  louse- infested populations. Epidemics may be expected in  wars,  famines,  and  other  conditions,  where people are overcrowded and malnourished. Poor personal hygiene encourages pediculosis. During epidemics,  all  contacts  and  perhaps  the  entire community  should  be  deloused  with  a  residual  in- secticide.  Administer  the  vaccine  to  susceptible persons,  if  directed. Immunization  is  not  required  for  international travel. Yellow Fever An  attack  of  yellow  fever  usually  results  in abrupt  signs  and  symptoms  of  fever,  headache, backache,  nausea,  vomiting  and  prostration. Later in the course of the disease, the heart rate slows  and  becomes  weaker,  and  there  is  a  de- creased output of urine. Bleeding may occur from the nose, mouth, and stomach. The stools become dark  colored  and  tarry  due  to  the  presence  of blood. Jaundice is mild early in the disease and becomes  pronounced  later.  The  mortality  rate may  be  very  high. Urban yellow fever (transmitted by the Aedes aegypti  mosquito)  has  not  occurred  in  the Americas since 1954. However, outbreaks of ur- ban  yellow  fever  are  now  reported  from  other countries/continents. Jungle yellow fever is found in several African countries and in Central and South  America. The infectious agent is the yellow fever virus. Man  and  the  Aedes  aegypti   mosquito   are   the reservoirs for urban yellow fever. The reservoirs for  jungle  fever  are  monkeys,  marsupials,  and forest  mosquitoes.  Man  acquires  the  disease  when bitten  by  an  infected  mosquito.  The  incubation period is from 3 to 6 days. Patients with yellow fever are infective from just prior to the onset of fever through the first 3 to 5 days of the illness. When  infected,  mosquitoes  remain  so  for  life. There is no treatment other than supportive measures. Preventive  measures  against  urban  yellow fever  are  primarily  through  eradication  of  the Aedes  aegypti  mosquitoes.   Vaccination   for   hu- mans  is  also  indicated.  Jungle  yellow  fever  can be controlled best by immunizing all persons who work  or  visit  endemic  areas.  Any  person  who enters these areas should use protective clothing, repellents, and bed nets. Management  of  patients,  contacts,  and  the nearby environment includes patient blood isola- tion precautions. In rural areas, deny mosquitoes access to patients for at least 5 days after the onset by screening, spraying with residual insecticides, and  using  bed  nets.  Insecticides  should  be  applied in all houses in the area. As part of the investigation, question the pa- tient about all places visited 3 to 6 days prior to the  onset  to  determine  where  yellow  fever  was  ac- quired (focus), and place all persons visiting the focus under surveillance. Survey suspected areas for  mosquitoes  that  transmit  the  disease  and eradicate them with approved insecticides, if pos- sible. Investigate deaths and mild illnesses with fever in the area to determine if yellow fever was involved. International measures require that ships, air- craft,  and  land  transportation  arriving  from  areas where yellow fever is endemic will follow regula- tion  outlined  in  International  Health  Regulations. Many  countries  require  a  valid  international  certi- ficate of yellow fever vaccination when traveling through  or  from  yellow  fever  areas.  The  certificate is  valid  from  10  days  after  vaccination  through the next 10 years. HEALTHFUL  LIVING  ASHORE AND   AFLOAT As a Medical Department representative, you will often be called upon to help ensure that all hands  have  healthful  living  conditions,  both ashore and afloat. This manual gives only a rough outline of your responsibilities. To perform ade- quately  in  this  area,  you  must  become  familiar with   the   BUMED/NAVMEDCOM   Instructions in the 6200 series, the  Manual  of  Naval  Preventive Medicine  (NAVMED  P-5010),  and  other  appli- cable   manuals   and   publications   that   may   be referenced  or  become  available  to  you. FOOD  SANITATION Foodborne illnesses are an ever-present danger in  the  military  environment.  They  pose  a  real threat to the health and morale of our personnel. To  prevent  their  occurrence,  one  must  ensure  that all foods are procured from approved sources and processed,   prepared,   and   served   with   careful adherence  to  recommended  sanitary  practices. The majority of foodborne illnesses can be traced to  food  that  has  been  prepared  too  far  in  advance; inadequate refrigeration; disregard   for temperature  and  time  factors;  or  food  service  per- sonnel who ignored or are inadequately trained in food handling techniques. These points need to 11-25