﻿ENTOMOLOGICAL 
  ASPECTS 
  OF 
  AN 
  OUTBREAK 
  OF 
  SLEEPING 
  SICKNESS. 
  345 
  

  

  epidemic. 
  The 
  danger 
  of 
  direct 
  transmission 
  of 
  human 
  trypanosomiasis 
  is, 
  as 
  I 
  

   saw 
  clearly, 
  by 
  no 
  means 
  limited, 
  however 
  few 
  the 
  trypanosomes 
  in 
  the 
  peripheral 
  

   blood 
  — 
  and 
  in 
  some 
  of 
  the 
  cases 
  examined 
  by 
  Maclean 
  while 
  I 
  was 
  with 
  him 
  they 
  

   were 
  numerous 
  — 
  as, 
  I 
  understand, 
  is 
  the 
  rule 
  in 
  infection 
  with 
  T. 
  rhodesiense 
  ; 
  and 
  

   it 
  seems 
  easy 
  to 
  understand 
  how, 
  under 
  conditions 
  so 
  favourable 
  to 
  intensive 
  direct 
  

   transmission, 
  the 
  pathogenicity 
  of 
  the 
  trypanosome 
  might 
  mount 
  rapidly 
  and 
  bring 
  

   about 
  the 
  well-known 
  special 
  virulence 
  of 
  early 
  cases, 
  taking 
  place 
  before 
  any 
  dimi- 
  

   nution 
  of 
  the 
  fly, 
  recovery 
  of 
  the 
  game, 
  extension 
  into 
  areas 
  in 
  which 
  game 
  was 
  to 
  

   some 
  extent 
  present, 
  or 
  more 
  orthodox 
  attenuating 
  factors 
  came 
  into 
  play. 
  

  

  The 
  presence 
  of 
  abundant 
  mosquitos 
  in 
  the 
  settled 
  country, 
  combined 
  with 
  the 
  

   alleged 
  absence 
  there 
  of 
  infections, 
  might 
  seem 
  an 
  argument 
  against 
  mechanical 
  

   transmission. 
  On 
  the 
  other 
  hand, 
  I 
  know 
  of 
  no 
  cases 
  or 
  records 
  from 
  which 
  it 
  seems 
  

   likely 
  that 
  mosquitos 
  have 
  transmitted 
  nagana 
  of 
  cattle, 
  and 
  it 
  is 
  possible 
  that 
  for 
  

   mechanical 
  reasons, 
  or 
  (perhaps 
  far-fetched) 
  as 
  a 
  matter 
  of 
  temperature, 
  the 
  night- 
  

   biting 
  mosquitos 
  that 
  alone 
  were 
  present 
  in 
  number 
  may 
  be 
  less 
  efficient 
  transmitters 
  

   of 
  trypanosomes 
  than 
  the 
  tsetses 
  and 
  Tabanids 
  or 
  than 
  the 
  two 
  day-biting 
  genera 
  

   of 
  mosquitos 
  (Stegomyia 
  and 
  Mansonioides) 
  that 
  I 
  believe 
  are 
  especially 
  suspected 
  

   by 
  French 
  investigators. 
  

  

  A 
  further 
  criticism 
  might 
  be 
  to 
  the 
  effect 
  that 
  the 
  European 
  rarely 
  comes 
  into 
  

   the 
  intimate 
  contact 
  with 
  sick 
  natives 
  in 
  the 
  presence 
  of 
  tsetses 
  that 
  I 
  have 
  

   described, 
  and 
  wears 
  clothes, 
  yet 
  cases 
  of 
  trypanosomiasis 
  in 
  Europeans 
  are 
  not 
  

   infrequent. 
  Against 
  this 
  it 
  may 
  be 
  said 
  that 
  it 
  is 
  not 
  argued 
  that 
  cyclical 
  

   transmission 
  is 
  not 
  also 
  a 
  factor 
  (and, 
  if 
  the 
  disease 
  is 
  purely 
  human, 
  a 
  highly 
  

   important 
  one) 
  ; 
  and, 
  in 
  addition, 
  the 
  question 
  of 
  the 
  relative 
  susceptibility 
  of 
  the 
  

   races 
  has 
  never 
  been 
  adequately 
  studied. 
  The 
  aggregate 
  sojourn 
  of 
  white 
  men 
  in 
  

   sleeping 
  sickness 
  foci 
  is 
  infinitesimal 
  compared 
  with 
  that 
  of 
  the 
  natives, 
  yet 
  even 
  

   where 
  only 
  a 
  rare 
  native 
  becomes 
  ill 
  Europeans 
  have 
  contracted 
  the 
  disease, 
  

   though 
  their 
  porters 
  have 
  apparently 
  escaped. 
  

  

  XIX. 
  — 
  The 
  Relation 
  of 
  the 
  Game 
  to 
  the 
  Outbreak. 
  

  

  The 
  oedema 
  that 
  was 
  commonly 
  present 
  and 
  the 
  identity 
  of 
  the 
  insect 
  vector 
  

   suggest 
  that 
  the 
  infection 
  was 
  one 
  of 
  T. 
  rhodesiense, 
  and 
  even 
  the 
  rather 
  long 
  duration 
  

   of 
  the 
  cases 
  that 
  told 
  against 
  this 
  view 
  is 
  explicable 
  on 
  the 
  fact 
  that 
  the 
  epidemic 
  

   had 
  already 
  lasted 
  some 
  years 
  ; 
  but 
  a 
  decision 
  on 
  the 
  point 
  was 
  lacking 
  when 
  I 
  left, 
  

   and 
  several 
  theories 
  were 
  still 
  tenable 
  as 
  to 
  the 
  origin 
  of 
  the 
  outbreak. 
  

  

  If 
  the 
  Trypanosome 
  is 
  T. 
  gambiense. 
  

  

  It 
  seemed 
  to 
  us 
  at 
  the 
  time 
  of 
  our 
  investigation 
  quite 
  probable 
  that 
  the 
  outbreak 
  

   had 
  been 
  initiated 
  by 
  some 
  infected 
  person 
  or 
  persons 
  with 
  the 
  Belgian 
  or 
  British 
  

   forces 
  that 
  collected 
  here 
  to 
  attack 
  Neumann 
  in 
  1917 
  when 
  he 
  broke 
  back 
  from 
  the 
  

   south 
  of 
  the 
  territory 
  to 
  Ikoma. 
  

  

  A 
  portion 
  of 
  this 
  force, 
  which 
  included 
  numerous 
  carriers 
  from 
  Uganda 
  who 
  

   accompanied 
  the 
  Belgians, 
  was 
  landed 
  at 
  points 
  nearer 
  to 
  Ikoma. 
  Another 
  portion 
  

   was 
  stated 
  definitely 
  by 
  the 
  chiefs 
  and 
  other 
  natives 
  to 
  have 
  passed 
  through 
  and 
  

   camped 
  in 
  the 
  villages 
  of 
  Igombe, 
  Luguru 
  and 
  other 
  parts 
  of 
  the 
  country 
  now 
  infected 
  

   " 
  at 
  the 
  time 
  of 
  the 
  ripening 
  of 
  the 
  crops," 
  and 
  further 
  contact 
  with 
  the 
  inhabitants 
  

   was 
  established 
  through 
  the 
  fact 
  that 
  the 
  latter 
  also 
  were 
  impressed 
  as 
  carriers 
  and 
  

   marched 
  with 
  the 
  imported 
  carriers. 
  

  

  On 
  the 
  other 
  hand, 
  the 
  disease 
  may 
  have 
  lingered 
  unknown 
  in 
  some 
  spot 
  in 
  our 
  

   own 
  territory 
  since 
  the 
  great 
  epidemic 
  on 
  the 
  Victoria 
  Nyanza. 
  There 
  was 
  much 
  

   movement 
  of 
  the 
  Wasukuma 
  people 
  in 
  1917 
  and 
  1918, 
  as 
  I 
  shall 
  describe 
  below 
  ; 
  

   and 
  this, 
  or 
  the 
  wandering 
  of 
  infected 
  individuals 
  from 
  elsewhere, 
  may 
  have 
  brought 
  

   'them 
  in 
  contact 
  with 
  infection. 
  

  

  