[leish-l] Leishmaniasis in Brazil

[Richard Ashford]

Dear Jorge,

How nice to hear from you, and happy new year to you too, though its 
getting a bit late for that.

Of course I completely disagree with you!  I had thought Ralph Lainson and 
Jeff Shaw were the last remnants of the chagasists. It might be nice for 
practical purposes to have different names for the organism in two 
continents, but this contradicts various basic taxonomic essentials. This 
is not a matter of splitters and lumpers, it is a matter of basic rules.

First, the 'rules of nomenclature' specifically prohibit the provisional 
naming of putative species. Second, (see my recent letter with Gediminas 
Valkiunas in TiP) natural host range, like geographical range is not a 
valid taxonomic character. The 'single species null hypothesis' (I'd love 
to see a reference for this: it states that two organisms must be regarded 
as conspecific unless they can be shown to be different) is one of the most 
important principles in taxonomy. Without it, all zoogeography and study of 
host specificity become circular arguments. Do you need more?

I agree with you that the visceralising parasites are best treated as 
subspecies: L. d. donovani and L. d. infantum. This is because even these 
ones are not reliably separable in every instance, and because there are 
good differences in their biological potential, which correlate reasonably 
well with geography. So, if subspecies are used, these closely mimic 
subspecies of sexual organisms.

The validity of 'archibaldi' is another question.  As things stand this 
name has no validity at all because any existing definition of it is very 
inadequate. Whether or not the insight of Lainson & Shaw, that there may be 
two forms in Africa, one in Sudan, that behaves like donovani proper 
(affects all ages, plenty of PKDL) and one in Kenya that behaves a little 
more like infantum (many subclinical cases little or no PKDL), proves to be 
related to valid taxonomic character states, is the subject of our study at 
present. Whatever the answer, I very much doubt that the name archibaldi 
will survive.

I still maintain that the continued use of 'chagasi' masks the real and 
significant similarities between the various foci. And, anyway, if you want 
to use technical taxonomic terms, it is really essential to follow the 
rules. If you wanted to differentiate them, why not use vernacular terms 
such as NWZVL and OWZVL? This will be adequate till someone finds the 
reservoir host of Sudanese or Kenyan VL.

Well I guess these chat lines would be boring if everybody agreed on all 
the issues!

All the best,

Dick

--On 16 January 2003 08:30 -0500 "Arias, Dr. Jorge (WDC)" 
<ariasjor at paho.org> wrote:



Dear Dick,
First of all, Happy New Year!
 I think one difference is that of "splitters" and "clumpers". We see it
 throughout systematics.

 True that Le. chagasi cannot be differentiated from Le. infantum with the
 tool we presently have.

 For those that work with the leishmanias, I believe that there is little
 doubt that this organism was probably introduced from the Old World
 fairly recently, and perhaps at different times to different parts of the
 New World. I assume this because of the spottiness of its distribution
 throughout the Region.

 However there is quite a bit of clinical and epidemiological data (such
 as different genera of vectors) that seems to warrant the separation
 these two species of Leishmania. Maybe the correct procedure would be to
 consider them as subspecies (Le. i. infantum, Le. i. chagasi and maybe
 even include Le. i. archibald)?

 I am particular to the "splitting" into two species because it also
 allows easier management of my technical cooperation since there is a
 great difference in the population that it afflicts and because possible
 control interventions that could be implemented are also different in the
 two areas.

 We must also consider that if, sometime, differentiating characteristics
 are found, it will be easier to manage the "split" literature than the
 "clumped" literature.

 Have a good year,

 Regards,

 Jorge
 Jorge R. Arias, Ph.D.
 Regional Advisor
 Pan American Health Organization
 525 Twenty-third Street N.W
 Washington, D.C. 20037
 Tel +1 (202) 974-3271
 FAX +1 (202) 974 3565
 ariasjor at paho.org
 www.paho.org/dengue