Estimation of the minimum number of leishmania major amastigotes required for infecting phlebotomus duboscqi (diptera: psychodidae)

Background. Leishmaniasis is a vector-borne disease in which Leishmania parasites are transmittedby the bite of phlebotomine sand flies. Amastigotes are ingested by the sand fly vector with ablood meal taken from an infected host. This is followed by their differentiation into metacyclicpromastigotes which are selectively released and permitted to migrate interiorly so as to makethem available for transmission by bite. However, the actual number of amastigotes ingested bythe sand fly in the blood meal is not known.Objective: Toinvestigate the minimum number of Leishmania major amastigotes required to causean infection in Phlebotomus duboscqi following an infective blood meal.Design: A laboratory based study.Setting: Centre for Biotechnology Research and Development, Kenya Medical Research institute, Nairobi.Results: Dissection of all fed sand flies at six days post-infective blood meal revealed that bloodcontaining one amastigote per 0.3µl in a total volume of 0.5ml was able to cause an infection in thesand flies, but very few sand flies got infected (7.6% and 9.6% respectively). Concentrations of tenamastigotes per 0.3µl in 0.5ml gave infection rates of 35.4% and 26.3% respectively, suggesting thateven when the concentration of amastigotes in a bloodmeal was high, not all sand flies feeding onit were able to pick up the parasites.Conclusions:These observations suggests that one amastigote is sufficient to cause an infection toa sand fly and as a result of multiplication in the gut and the existence of mechanisms that increasethe number of infective bites delivered by a female sand fly they are able to sustain the transmissionof leishmaniasis in an area

Abundances and nocturnal activities of phlebotomine sandflies (Diptera : Psychodidae) in termite hills and animals burrows in Baringo District; Kenya

The abundance of phlebotomine sandflies was studied in a leishmaniasis endemic area in Baringo District; Rift Valley Province; Kenya. This was based on sandfly behaviors at night in their natural habitats of termite hills and animal burrows. Sandflies were collected with an entry-exit trap which has a sieve fixed at the middle to control sandfly movements. Flies were trapped from 1800-0600 hours. Phlebotomus martini (Parrot) were significantly more abundant in termite hills than in animal burrows (P 0.05). Phlebotomus duboscqi (Neveu-Lemaire) were found to favour animal burrows more than termite hills (P 0.05). Nocturnal movements and activities showed that the majority of the sandflies were exiting from termite hills and animal burrows from 1800-2400 hours while from 2400-0600 hours; the majority of the sandflies were entering termite hills and animal burrows (P0.05). Sergentomyia (Theodor) species showed mixed preferences for these two habitats. Sergentomyia schwetzi (Aldler; Theodor et Pam favoured termite hills more than animal burrows but S. clydei (Sinton) showed great preference for animal burrows. The nocturnal activities or preferences of habitats by phlebotomine sandflies have epidemiological significance in that control measures can be directed to these habitats with a certain degree of accuracy for the vectors of visceral and cutaneous Leishmaniasis in Kenya

Screening of metal ion chelators against Leishmania donovani-infected Syrian hamsters

Leishmania donovani-infected Syrian hamsters were treated intraperitoneally with 0.23 mmoles/kg/day of EDTA; EGTA; HEEDTA and 100 mg/kg/day of Pentostam R. The control group received 0.1 ml of phosphate buffered saline. After 30 days of treatment; the animals were sacrificed. Of the Pentostam-treated animals; 5 out 6 had negative spleen cultures; while all the chelator and PBS-treated ones yielded parasites. While all the Pentostam-treated hamsters yielded had negative bone marrow cultures; only 1 out of 6 HEEDTA-treated hamsters yielded parasites. Spleen; liver and bone marrow parasite-loads calculated from chelator-treated animals were consistently significantly higher than for Pentostam-treated animals. These results suggest that although metal ion chelators have some antileishmanial potential; their in vivo activity against L. donovani is low compared to Pentostam

Comparison of Giemsa and acridine orange stains for the diagnosis of Leishmania donovani in biopsies of infected hamsters

Identical impression smears of spleen; liver and bone marrow biopsy materials from Leishmania donovani-infected hamsters were stained using either acridine orange or Giemsa. Spleen parasite-loads calculated from the two stains for identical biopsy material were significantly different from each other. However; liver and bone marrow parasite-loads calculated from either Giemsa-stained or acridine orange-stained biopsies were not significantly different from each other. This study has shown that acridine orange; which is a quick and simple technique; has great potential in the diagnosis of kala-azar when liver and bone marrow biopsies are used

Determination of the optimal EDTA and Pentostam concentration in the treatment of Leishmania donovani-infected laboratory animal rodent models

The objective of this study was to undertake a dose response study to determine the optimal Pentostam and Ethylenediamine tetraacetic acid (EDTA) dose that could be used in the treatment of leishmania-infected golden hamsters or BALB/c mice for a period of 30 days. This pilot experiment was done using only one chelator; EDTA and the toxicity results obtained from this experiment formed the basis for the selection of a suitable chelator dose of this class for the future treatment of leishmania-infected laboratory animal rodent models. It is concluded that Pentostam concentrations beyond 600 mg/kg are highly toxic to mice and therefore unsuitable for use. Although Pentostam have been used to treat leishmania-infected BALB/c mice; this study has shown that a concentration of 100 mg/KG/day is the most suitable dose for use in the treatment of rodent animal models

Screening of metal ion chelators against Leishmania donovani-infected BALB/c mice

Previous in vitro experiments by Mbati et al. have shown that Ethylenediamine tetraacic acid (EDTA) and Ethyleneglycol-bis (B-aminoethyl ether) N;N;N1;N1; tetraacetic acid (EGTA) substantially reduce parasite burdens of leishmania donovani in either cell free media or when engulfed in mouse peritoneal macrophages. The objective of this study was to compare the activity of the same chelators against Leishmania donovani in BALB/c mice infected with a much lower parasite inoculum

Evaluation of the optimal inoculation of leishmania major culture-derived stationary phase promastigotes required to assess protective immune status in the vervet monkey model

"Vervet monkeys have been shown to be resistant to a homologous challenge of Leishmania major after an active infection followed by self cure responses. Confirmation of the protective immune status of such animals was demonstrated by exposing a group of 4 monkeys to multiple infected sandfly challenge. Two animals revealed small transient nodule formation while in the remaining two; no signs or symptoms were obvserved. In order to ascertain the level of promastigote challenge which was equivalent to such a ""natural"" fly challenge; 3 additional groups of immune vervet monkeys were challenged with 1x103; 1x104 and 105 stationary phase culture promastigotes in the presence of salivary gl and lysates. In all groups; there was no lesion development whatsoever. A second challenge of 1x106; 1x107 and 4x107 in these same animal groups; revealed self healing nodules in the group inoculated with 1x106 promastigotes whilst in the remaining 2 groups challeged at the higher levels; there was nodule formation which progressed to ulceration. A challenge dose of 1x105 culture promastigotes was thus considered to be optimal since this level of challenge in naive animals was demonstrated to result in ulcer formation when inoculated with salivary gland lysates."

Plasmodium falciparum infection rates in malaria vectors at two ecologically district sites in Kilifi Districts; Kenya

Transmission of Plasmodium falciparum was studied for one year at two ecologically different sites in Kilifi district. Anopheline mosquitoes were collected by three sampling methods and tested for P.falciparum sporozoites by ELISA. Anopheles gambiae s.l. was the predominant vector. Plasmodium falciparum sporozoite rates were 4.07 (20/491) and 2.17 (3/138) for An.gambiae s.l. at Sokoke and Kilifi town respectively. No sporozoite infections were detected in An.funestus or An.coustani. Transmission was year-round with highest levels occurring after the long rains (June to September). Entomological inoculation rates indicated taht each person could receive 8 infcetive bites per year at Sokoke; compared with 1.3 infective bites per year at Kilifi town. Our studies indicate taht the public health problem of malaria in Kilifi district is associated with extremely low levels of P.falciparum transmission by vector populations