Jean-Paul Gouteux

Loa loa and Mansonella perstans filariasis in the Chaillu mountains, Congo: parasitological prevalence

1934 Bantus and 379 Pygmies were investigated for Loa loa and Mansonella perstans filariasis in 7 villages in the Chaillu forest of the Congo. Bantus were more frequently infected with L. loa than Pygmies (18.9% of microfilariae carriers compared with 10.6%). In individuals over 30 years of age, males were more frequently infected than females. Microfilarial densities increased until the age of 20 years and then remained stable. Parasite load was not significantly different in the two ethnic groups. For mansonelliasis, the microfilarial rate was higher in the Pygmies (67.5% compared with 22.0%) and males of the 2 groups were more frequently infected than females. Microfilarial load was also higher in Pygmies than in Bantus (mean microfilarial densities (MfD 50) 13 and 2 respectively). In the Pygmy group, MfD 50 for M. perstans increased with age whereas it remained stable in the Bantus. 53.8% of the 249 questioned persons had experienced worm migration under the conjunctiva. Both ethnic groups were equally exposed to the vectors of L. loa and reasons for the difference in prevalence of microfilaria carriers are discussed. For mansonelliasis increased contact with vectors may explain the higher degree of infestation observed in Pygmies. Other filariases were infrequent in (Mansonella streptocerca), or absent from (Onchocerca volvulus and Wuchereria bancrofti), the study area.

Serodiagnosis of sleeping sickness in the Republic of the Congo: comparison of indirect immunofluorescent antibody test and card agglutination test

The card agglutination test for trypanosomiasis (CATT) was evaluated and compared to the classical immunofluorescent antibody test (IFAT) in the immunological diagnosis of Gambian trypanosomiasis. Tests were performed on serum and whole blood. Cross-reactions were found in the CATT with sera from patients suffering from parasitic infections other than sleeping sickness, but could be largely overcome by selecting 1/10 as the specific threshold dilution. At 1/40 dilution no false positive result was observed in the IFAT. At the specific threshold dilution, the sensitivity of IFAT was 94.7%, compared with 91.6% for the CATT. On whole blood, a more convenient sample in the field, IFAT specificity (100%) was greater than that of the CATT (94.3%), as was its sensitivity (92% compared with 82.5%). In view of its simplicity and rapidity of execution, the CATT is an efficient serological test to detect new foci. When greater sensitivity is required, IFAT should be preferred to CATT.

Current considerations on the distribution of Glossina in west and central Africa

Tsetse distribution maps are a useful tool for both research workers studying trypanosomiasis and animal and human health authorities. They enable the potential vectors in the country to be identified and provide rapid information about their geographic distribution. Considerable work is involved in drawing up these maps, including the compilation of publications, unpublished reports and often the examination of entomological collections. These maps however require frequent up-dating. Ford and Katondo revised their first edition of tsetse distribution maps (1971, 1973) in 1975 and 1977. These maps were revised again by Katondo (1984) and subsequently by Moloo (1985). The revision by Moloo notably included the presence of Glossina nashi Potts 1955 in Gabon, where recent captures have been simultaneously recorded by Itard et al. (1984) and Leack and Jannin (1984). Until now this species had been recorded in Gabon by the observation of a single specimen only, reported by Machado (1959). The publication by Moloo (1985) includes clear synoptic tables and represents a significant event in that it is the most recent revision. We would like to contribute by up-dating records and also clarify some points which, in our opinion, raise difficulties. Recently, Gouteux et al. (1987) reported the discovery of G. calliginea in the Congo and the new species G. frezili, occurring in the Congo and Gabon (Gouteux, 1987). The presence of G . medicorum in Zaire and the Central African Republic should be investigated. Indeed, in a recent review, Makumyaviri (1986) did not mention this species in Zaire, nor did Finelle et al. (1963) in the Central African Republic. The presence of G. medicorum in Gabon, recorded originally by Maillot (1956, 1961), refers in fact to G. frezili (Gouteux, 1987). On the other hand, Moloo (1985) did not record G. medicorum in Togo or Guinea (Conakry) although it had been reported in Togo by Rickenbach (1961) and in Guinea by Maillot (1961). The presence of G . calliginea in Ghana and the Central African Republic should, according to

Field trials of various models of the pyramid trap on Glossina palpalis in the Congo

Preliminary trials of 12 models of the pyramid trap were carried out in the Congo on Glossina palpalis palpalis (Robineau‐Desvoidy) using Latin square designs. The models were compared with the standard trap with which they differed either in the shape of the pyramid, the addition of a royal blue cloth skirt, or the pattern of the blue‐black screen. A decrease in height and/or volume of the pyramid significantly reduced the capture rate. The standard tetrahedral pyramid was significantly superior to both the regular tetrahedral and the trihedral pyramid. The addition of a royal blue cotton skirt modified both the attractiveness and effectiveness of the trap. However, although the attractiveness was probably increased, the skirt may have deterred the flies from entering the pyramid; the best results were obtained with the largest openings. The modification of the blue‐black screen pattern may be a way to increase the attraction of flies to the trap. Although no model was found to be significantly superior to the standard, certain gave interesting results which should be investigated further.

Current considerations on a Loa loa simian reservoir in the Congo

Human filariasis due to Loa loa is confined to the tropical rain-forest of Africa. In the same area, simian populations are infected with parasites which have no clear-cut morphological differences with human Loa and exhibit a nocturnal microfilarial periodicity (Duke and Wijers, 1958). Chrysops lungi and C. centurionis are probably responsible for their transmission among monkeys (Duke, 1955). Although it appears that human and simian strains of Loa have evolved in two separate host-vector complexes (Duke and Wijers, 1958), the possibility of a transmission of simian Loa to man cannot be ruled out. Fain et al. (1974) did observe in Zairian patients from the Mayumbe area Loa microfilariae with a nocturnal periodicity. On-the other hand, simian loiasis observations showing a marked diurnal periodicity were reported by Wanson and Rodhain (1953) and Fain (1978). It is most unlikely that C. Iangi and C. centurionis, which are strictly zoophilic, would be responsible for the transmission from monkey to man. Anthropophilic Chrysops species (C. silacea and C. dimidiata) are the only potential vectors (Duke, 1955). In our study area in the Congo, the Chaillu mountains, 5189 anthropophilic flies have been examined in one year. Of these, 3848 were C. silacea (74.2%) and 1341 were C. ditnidiata (25.8%). Host preferences of anthropophilic Chrysops were investigated with a view to identifying possibilities of transmission of Lou between simian and human hosts. To this end a total of 408 blood-meal samples from C. silacea (262 flies) and C. dimidiata (146 flies) were analysed according to a procedure described by Staak et al. (1981). 88.9% and 90.4% of the samples from C. silacea and C. dimidiata, respectively, originated from man, and the rest from hippopotamus, rodents, wild pigs, wild ruminants and monitor lizards. No bloodmeal from monkey was identified. Despite their propensity for coming into contact with monkeys at canopy level (Duke, 1955), our results show that C. silacea and C. dimidiata feed mainly on man and cannot be responsible for the transmission of parasites between simian and human hosts in that part of the Congo.