Besnard, R.

Gentile, B.

Le Pont, François

Pajot, François-Xavier

Horizon / Pleins textes

112 
TRANSAC~IONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE, VOL. 76, No. 1, 1982 
r 
Epidemiology of leishmaniasis in French Guiana 
F. X. PAJOT’, F. LE  PONT^, B. GENTILE’ AND R, BESNARD’ 
‘Office de la Recherche Scientifque et Technique Outre-Mer, O R S T O M  Centre, B.P. No 165, 97301 Cayenne 
cédex, French Guiana; ’Institut Pasteur of French Guiana, B.P. No. 304,9730s Cayenne cédex, French Guiana 
Summary 
Lutzomyia umbratilis is coniîrmed as the vector of 
Leishmania braziliensis guyanensis, the cause of “pian 
bois” in man in French Guiana. Although spending 
most of the year in the forest canopy, this sandfly is 
abundant at ground level for about two weeks at the 
beginning of the long rainy season. The maximum 
number of infective bites per man per hour (3.9) was 
reached at the end of November 1979. Infections were 
found in one of seven Potos jbvus, seven of 15 
Choleopus didactylus and two of 19 rodents examined. 
C. didactylus seems likely to be the main reservoir. 
In French Guiana, the number of cutaneous 
leishmaniasis cases has increased notably in the last 
three years (454 in all). These cases are connected 
with the clinical form locally known as “pian-bois” 
(forest yaws) caused by the parasite Leishmania 
b r a z i l i d  guyanensis. A first series of entomological 
observations made in 1978, and during the first three 
months of 1979, showed that the vector of this disease 
was very likely the phlebotomine sandfly Lutzomyia 
umbratizis Ward & Fraiha (see LE PONT et al., 1980), a 
species already noted as the vector of L. braziliensis 
g u y a m ’ s  in Para State, Brazil (LAINSON et aZ., 1976) 
and suspected (under the name Lu. anduzei) of being 
the vector of this parasite in French Guiana (FLOCH & 
ABONNENC, 1952) and in Surinam (WIJERS & LIN- 
GER, 1966). 
A series of observations made during 1979 and 1980 
enabled us to: (i) confirm the role of Lu. umbratilis in 
the transmission of “pian-bois” in French Guiana; (ii) 
collect important information on the bio-ecology and 
the natural infection rate of this species; (iii) specify 
the epidemiology of this form of leishmaniasis in 
primary forest and in a village situated in a forest area 
recently populated; and (iv) to show what is likely to 
be the main reservoir of the parasite in the two 
principal, active foci of cutaneous leishmaniasis 
(Cacao and Sinnamary). 
In French Guiana, Lu. umbratilis is essentially an 
arboreal, forest sandfly, and its population increases 
as one reaches the forest canopy. Infrequent at ground 
level, except for a short period of two weeks during 
the first rains of the long rainy season and, to a lesser 
extent, for a short time when the rains slacken before 
the dry season, Lu. umbratilis populations are heavy in 
the canopy. Here, populations are very dense at the 
end and, especially, at the beginning of the rainy 
season. At ground level, Lu. umbratilis represents only 
a small fraction of the sandflies which are aggressive to 
man, except at the end and the beginning of the rainy 
season. On the other hand, in the canopy, it is always 
the dominant species, representing 75 to 98% of the 
sandtlies collected on human bait. This sandfly is not 
generally aggressive during the day at ground level, 
but is very susceptible to the effects of intrusion and 
attacks when one enters its biotope and upsets its 
habitat. On the ground and in the under-storey, its 
activity is predominantly after dusk, whereas in the 
canopy it is especially active at twilight, activity 
diminishing steadily thereafter (LE PONT & PAJOT, 
1980). Females seem to be opportunist in their choice 
of hosts. They are very partial to two-toed sloths, an 
animal found quite frequently in foci of leishmaniasis 
and which is a carrier of L. braziliensis guyanensis (see 
GENTILE et al., LAINSON et al., 1981). 85% of the 
infections we have found in Lu. umbratilis in primary 
forest of French Guiana are distinctly peripylarian 
and may be attributed to L .  braziliensis guyanensis, as 
confirmed for one of them (Lainson, personal com- 
munication). In the canopy, the infection rate of 
females is high during the dry season and beginning of 
the rains, reaching up to 21.6% (October 1979). The 
maximum number of infective bites per man, per 
hour was 3.9, which was reached at the end of 
November 1979. At ground level, the infection rate 
reached 15% at the same time and the number of 
infective bites per man, per hour was 1-3 (LE PONT & 
PAJOT, 1980). It therefore seems that man is at 
greatest risk at the beginning of the rains after the dry 
season (end of November). A study of the human 
cases of leishmaniasis occurring during the last three 
years shows that many of them became apparent in 
December and January, indicating that infection was 
acquired at the beginning of the rainy season, when 
infected female Lu. umbratilis are exceptionally abun- 
dant on the forest floor for a period of about two 
we_e_ks. 
As human occupation of the natural environment 
decreases, so the infection rate Óf female Lu. umbrati- 
lis increases (LE PONT & PAJOT, 1980), but the role of 
Lu. umbratilis in transmitting leishmaniasis in a 
heavily populated forest environment remains fun- 
damental. At Cacao, a forest village inhabited by 
Asians (Hmongs), numerous cases of leishmaniasis 
have occurred in men, women and children living in a 
group of houses situated on the edge of the village, 
whereas in the centre of the village, only men and a 
few children contracted this disease. We have found 
(LE PONT & PAJOT, 1981) some dwellings on the 
outskirts, about 30 to 70 m from a remaining, isolated 
patch of forest, which housed infected people of all 
ages. Here, despite heavy degradation of the natural 
environment, numerous Lu. umbratilis females re- 
mained, some 
of the nearest 
leishmaniasis. 
umbratilis live 
and represent - 1  
area. Lu. umbratilis w &h$ onl! 
the verandas of the L o n g  di 
113 I F .  x. PAJOT et al. 
74 mammals belonging to 5 orders and 14 species 
(GENTILE et al., 1981) were examined for Leishmania 
infection. One of seven (14.3%) kinkajous, Potos 
flavus, seven of 15 (46.7%) sloths, Choloepus didactylus 
and two Proechimys sp. of 19 (10.5%) rodents were 
found to be infected with Leishmania. A strain 
isolated from a sloth and sent for identification to the 
Instituto Evandro Chagas of Belém, Para, Brazil, was 
found to be indistinguishable from L. braziliensis 
guyanensis strains already isolated from man, sand- 
flies, ant-eaters and sloths in North Brazil (LAINSON 
et al., 1979, 1981a, 1981b). 
Thus, in French Guiana, “pian-bois” or leish- 
maniasis due to L .  braziliensis guyanensis seems to 
have an enzootic cycle occurring especially in the 
upper storeys of the forest. The two-toed sloth seems 
most likely to be the main reservoir of this disease and 
was found to be infected in the two main foci studied 
(Cacao and Sinnamary). The role of the kinkajou and 
possibly other arboreal mammals remains to be 
studied more in detail. Man is infected following an 
upheaval of the forest environment (e.g. by tree 
felling) or an intrusion into the resting places of Lu. 
umbratilis but, most of all, as the study of recent 
human cases has shown, during the first rains of the 
long rainy season, the time of year when Lu. umbratilis 
are particularly abundant at ground level. Man may 
also be infected in his home when this is situated close 
to a silya-tic focus. 
This cycle of leishma&asis in French Guiana is 
reminiscent of one of the principal cycles of leish- 
maniasis due to L .  braziliensis panamensis in Panama 
involving the sandfly Lu. trapidoi and the two-toed 
sloth C. hoffmani, a cycle which demonstrates the 
close relationship between hosts, vectors and parasites 
in the forest canopy (HERRER et al., 1971; HERRER &
CHRISTENSEN, 1976). 
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Accepted for publication 21st April, 1981 


Epidemiology of leishmaniasis in French Guiana

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