[leish-l] Reply to Dick Ashford's question.

[Jeffrey J Shaw]

	As usual Dick's communications are provocative.
	In respect to the ages that become infected with the visceral parasites I 
have the following comments.
	The Wellcome Parasitology recorded cases of visceral leishmaniasis in 
young adults working in sawmills that were situated along the edge of a 
newly opened road in the Igarape-Mirim region, Pará State. Over a period of 
years cases in young adults all but disappeared and cases began to appear 
in children (0-10 years old). In Pará State cases in adults are in general 
rare and most are in young children with a tendancy for there to be more in 
boys.
	Attention was drawn to endemic visceral leishmaniasis in the Camera 
municipality of Pará State by the death of a young man in a Belém hospital. 
However, in spite of a very high incidence in dogs, which was and probably 
still is in the order of 40%, human cases are rare and again more occur in 
young children. However, a skin test survey showed a high percentage of 
reactors in adults.
	These observations lead me to suspect that when the disease moves in to an 
area cases occur in all age groups then as the canine disease becomes 
endemic immunity is acquired. HIV in Europe suggests a similar pattern i.e. 
lots of people becoming infected but few clinical cases.
	A possible modulating factor is the sand fly biting rate. As this 
increases with the size of the vector population it is possible that saliva 
antibodies downgrade clinical infection as shown experimentally by David 
Sack's group. Genetically controlled susceptibility is another disease 
modulating factor which may be important.
Thank you all for your support last year.
Best wishes to everybody for 2003
Jeffrey Shaw
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