Simuliid Blackflies (Diptera: Simuliidae) and CeratopogonidMidges (Diptera: Ceratopogonidae) as Vectors of Mansonella ozzardi (Nematoda: Onchocercidae) in Northern Argentina

Vol.96(4): 451-458, May 2001

AJ Shelley/⁺, S Coscarón*

Department of Entomology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK

*Museo La Plata, La Plata, Argentina

Mansonella ozzardi, a relatively non pathogenic filarial parasite of man in Latin America, is transmitted by either ceratopogonid midges or simuliid blackflies. In the only known focus of the disease in north-western Argentina the vectors have never been incriminated. This study investigated the potential vectors of M. ozzardi in this area. The only anthropophilic species of these Diptera families biting man at the time of the investigation were Simulium exiguum, S. dinellii, Culicoides lahillei and C. paraensis. Using experimentally infected flies S. exiguum and both species of Culicoides allowed full development of microfilariae to the infective stage, with C. lahillei being a more competent host than S. exiguum. Based on these data, biting rates and natural infectivity rates it is probable that at the begininning of the wet season C. lahillei is the main vector of M. ozzardi and both C. paraensis and S. exiguum secondary vectors. Additionally, it was found that a single dose of ivermectin was ineffectual in eradicating M. ozzardi from infected individuals in this area.

Key words: Mansonella ozzardi - Simuliidae - Ceratopogonidae - Simulium exiguum - Simulium dinellii - Culicoides lahillei - Culicoides paraensis - Argentina

Mansonella ozzardi is a filarial parasite first described from Guyana (then British Guiana) at the end of the last century and now known to occur in Central America in the Yucatan Peninsula of Mexico through to northern Argentina in South America, as well as on various Caribbean islands. It is relatively non pathogenic, its main importance lying in its morphological similarity to the highly pathogenic Onchocerca volvulus. This is especially relevant in Brazil where the two species are sympatric in parts of the Amazônia onchocerciasis focus. Attempts at controlling mansonelliasis have been few, but recent reports indicate that ivermectin may be effective as a microfilaricide. Various anthropophilic Diptera were examined before it was shown that M. ozzardi is transmitted by Culicoides furens and possibly C. paraensis in the Caribbean Island of St Vincent (reviewed by Buckley 1934, Shelley & Shelley 1976). Later, simuliid species were incriminated as vectors in South America. This gave rise to the hypothesis that two races of M. ozzardi exist: one in the Caribbean islands and Mexico transmitted by ceratopogonid species, and the other transmitted by simuliid species in Panama and South America (Nelson & Pester 1962). Currently, only Culicoides species are known to transmit in the Caribbean islands but both Simulium and Culicoides species are vectors in Central and South America (Table I), but no comprehensive studies have been carried out on the transmission of M. ozzardi and the relative competence of its vectors.

Several studies have been made on M. ozzardi in Argentina and these are reviewed in Romaña and Wygodzinsky (1950). Since then several reports have been published on communities in Argentina that are infected with this parasite (Undiano 1971, Jörg 1983, Minoprio et al. 1988, Remon-degui et al. 1988, Taranto & Castelli 1988). These studies indicate that mansonelliasis is confined to the provinces of Tucumán and Jujuy to the north of the country and affects mainly subsistence farming communities, largely formed in the past by the southern dispersal of indians from southern Bolivia. It has been shown that the parasite is relatively non pathogenic, although treatment with ivermectin has been carried out. Attempts at establishing the identity of the vector of M. ozzardi in Argentina have failed. Buckley (1934) and Romaña and Wygodzinsky (1950) cite previous experimental infection studies carried out in Argentina showing that Cimex (Hemiptera, Cimicidae) and Triatoma (Hemiptera, Reduviidae) bugs were not hosts, that microfilariae developed to the L1 stage in Anopheles tarsimaculatus, A. albitarsis and Aedes aegypti but not in A. pseudopunctipennis, A. argyritarsis and C. quinquefasciatus (Diptera, Culicidae). Romaña and Wygodzinsky (1950) showed that no development occurred in simuliids that had fed on M. ozzardi carriers, but that development did occur to the L2 stage in C. paraensis. Development to the L3 stage did not continue because of premature mortality of flies.

The objective of the current work was to discover the vector species of M. ozzardi in the mansonelliasis focus in northern Argentina.

MATERIALS AND METHODS

RESULTS

DISCUSSION

ACKNOWLEDGEMENTS

To Dr G Safarov and Dr J Arcaide of the Fraile Pintado Hospital for valuable orientation and use of laboratory facilities respectively; Dr G Spinelli for identification of the ceratopogonids; to Mr H Suligoy for assistance during field work and to Miss A Sanders for assistance in dissecting some of the material. Mr M Fritz kindly provided transport in the field.

REFERENCES

Table I | Table II | Table III | Table IV

The Royal Society and CONICET provided funding for the work.

⁺Corresponding author.Fax:44-1-071-938.9395.E-mail: ajs@nhm.ac.uk ; sixtoco@museo.fcnym.unlp.edu.ar

Received 23 May 2000.

Accepted 5 February 2001