J.A. Reynoldson

Failure of pyrantel in treatment of human hookworm infections (Ancylostoma duodenale) in the Kimberley region of North West Australia

A survey of 108 individuals from a coastal Aboriginal community in north Western Australia revealed that two species of gastrointestinal protozoan parasites (Giardia duodenalis--39.8%, Entamoeba coli--40.7%) and five gastrointestinal helminths (Hymenolepis nana--54.6%, Hookworm [Ancylostoma duodenale]--30.6%, Enterobius vermicularis--6.5%, Trichuris trichiura--2.8%, Strongyloides stercoralis 1.9%) were present. A total of 29 individuals infected with hookworm were offered treatment with either pyrantel pamoate at a single dose rate of 10 mg/kg body weight or albendazole (single 400 mg dose). Seven days after treatment stool samples were examined. Pyrantel had no significant effect against hookworm. In contrast, albendazole cleared hookworm infections completely and reduced the prevalence of Giardia. The former result suggests that locally A. duodenale is resistant to pyrantel and despite its relatively low cost and wide availability, should not be considered a drug of choice at this dose rate in the treatment of hookworm infections (A. duodenale) in endemic regions.

Albendazole: a more effective antigiardial agent in vitro than metronidazole or tinidazole

The effects of albendazole were assessed against Giardia duodenalis in vitro and compared with those of tinidazole and metronidazole. Trophozoite morphology, adherence and viability were markedly affected by albendazole, to a far greater extent than by either metronidazole or tinidazole. The results of this study, and in particular the superior potency of albendazole in vitro, are discussed with respect to its potential value as a new approach to the chemotherapy of giardiasis.

Activities of several benzimidazoles and tubulin inhibitors against Giardia spp. in vitro.

Previous studies in our laboratory have shown that albendazole is effective against Giardia spp. in vitro and in vivo, prompting an investigation of the effects of several related benzimidazoles (BZs) on the viability of this protozoan parasite. A range of BZs was tested, and their effects were compared with those of a number of microtubule inhibitors. The effects produced by the two types of drugs were markedly similar, namely, trophozoite detachment and distortion of morphology and general structure, indicating a potential antimicrotubule mode of action for BZs. Mebendazole, albendazole, and fenbendazole proved to be among the most effective BZs tested, exhibiting apparent irreversibility. Nocodazole, oxfendazole, and albendazole sulfoxide, among others, produced transient inhibitions only. Further studies are required to evaluate all available BZs and other antigiardial agents to ensure the development of the most effective and safest antigiardial agent possible.

Giardia - from molecules to disease

Summary Giardiais a parasitic protozoan which is attracting considerable interest worldwide. It can cause severe gastrointestinal problems in humans and has also been reported in a number of domestic and wild mammals. This book addresses major issues and new developments concerningGiardiaand giardiasis.

Efficacy of albendazole against Giardia and hookworm in a remote Aboriginal community in the north of Western Australia.

The parasitological, clinical efficacy and tolerability of albendazole in the treatment for both giardiasis and hookworm infection in a remote Aboriginal population was investigated. Albendazole at a dose rate of 400 mg daily for 5 days was highly effective in reducing hookworm egg numbers and both Giardia antigen and cysts. The 36.6% prevalence of Giardia prior to treatment fell to 12% between days 6 and 9, 15% for days 10-17 and rose to 28% between days 18 and 30. Tolerability and clinical efficacy were excellent. The effect of albendazole on hookworm was longer lasting than that on Giardia, reducing percent infection from over 76-2% on days 6-9 and zero by day 18-30 despite conditions highly conducive to rapid re-infection. We conclude that albendazole is highly efficacious against both parasites when used as described but that long term community benefit may require additional education programmes to avoid re-infection with Giardia although treatment strategies would seem appropriate for hookworm.

PCR-based DNA fingerprinting of Giardia duodenalis isolates using the intergenic rDNA spacer

The potential for the non-coding intergenic rDNA spacer (IGS) to DNA fingerprint Giardia duodenalis isolates was investigated. Conserved PCR primers, specific for the flanking large and small rDNA genes, were used to amplify the IGS from 52 in vitro-cultured Giardia isolates. Four distinct IGS-PCR size groups (1.35-1.6 kb) were observed, which correlated closely with the major genetic assemblages established previously for the same isolates using isoenzyme analysis. IGS-PCR size groups A (1.42 kb) C (1.4 kb) and D (1.35 kb) corresponded to isoenzyme assemblage A, and IGS-PCR group B (1.6 kb) to isoenzyme assemblage B. Amplified products from IGS-PCR size groups A and B, which contained 50/52 isolates, were subsequently digested with 8 different restriction enzymes and their profiles compared. Analysis separated isolates within each IGS-PCR size group into 2 distinct clusters which correlated almost exactly with the same genetic groups established previously using isoenzyme electrophoresis. Within each cluster, both methods exhibited a similar capacity to distinguish between Giardia genotypes although they established different genetic relationships between individual isolates. Much of the variability associated with the IGS was attributed to isolates harbouring multiple IGS-sequence types. Restriction analysis of IGS-PCR products amplified from cloned and parent lines of a human isolate BAH 39, which contains multiple IGS variants, showed that trophozoite populations are homogeneous with respect to the types of IGS-variants they maintain. Furthermore, in vitro culture of the cloned isolate BAH39c9 over a 6-year period also failed to reveal variation in IGS-PCR digestion profiles. These results suggest that IGS-PCR RFLP profiles are inherently stable. IGS-PCR analysis was successfully applied to 11 Giardia cyst samples highlighting the potential for this approach to genotype Giardia isolates without the need for in vitro culture.

Evaluation of the effects of albendazole and metronidazole on the ultrastructure of Giardia duodenalis, trichomonas vaginalis and Spironucleus muris using transmission electron microscopy

The three closely related parasitic protozoa, Giardia duodenalis, Trichomonas vaginalis and Spironucleus muris, all have very different sensitivities to albendazole and metronidazole. Ultrastructural studies reveal that the cytoskeletal elements of the ventral disk in G. duodenalis are affected by albendazole, whereas the other two parasites, neither of which possess this structure, are not affected by albendazole to the same extent. This suggests that albendazole may be having its primary affect on G. duodenalis by binding to cytoskeletal proteins and ultimately causing death of the parasite. Death may be occurring as the parasite loses its ability to adhere to the intestinal villi and obtain nutrients. Metronidazole showed a different pattern of activity against the three parasites. The evidence obtained from these ultrastructural studies supports the current theory that metronidazole adversely affects protozoa by disrupting inner cell membranes.

A comparison of the effects of a benzimidazole and the dinitroanilines against Leishmania infantum

Leishmania infantum promastigotes and amastigotes were axenically cultured and exposed to the known tubulin binding compounds, the dinitroanilines, trifluralin, benfluralin, pendimethalin, oryzalin and the precursor of the dinitroanilines, chloralin, as well as isomers of chloralin and trifluralin and to the benzimidazole, albendazole. Drug induced inhibition was observed using [3H]thymidine uptake compared with untreated controls. In vitro analysis demonstrated a significant difference in the activity of five of the seven dinitroanilines between both life cycle stages of L. infantum. The amastigotes were 20-times more sensitive to chloralin and its isomer than to the dinitroanilines whereas the promastigotes were similar in sensitivity to the dinitroanilines and to chloralin and its isomer. This interesting finding suggests that the dinitroaniline precursors may have different target sites in the amastigotes to those within the promastigotes. Additionally, both chloralin and its isomer, and to a lesser extent benfluralin, caused a substantial stimulation of thymidine incorporation (up to 50%) at low concentrations. Dose response analysis suggests that the dinitroanilines may have more than one mode of action against L. infantum amastigotes and promastigotes. The inhibitory effects of the dinitroanilines against L. infantum vary from previous findings using the dinitroanilines against other Leishmania spp. The 348 base pair DNA sequence coding for beta-tubulin from amino acid residues 132 to 248 was obtained for L. infantum and used to compare the in vivo efficacy of albendazole with predicted activity based on beta-tubulin sequences of known benzimidazole sensitive protozoa. The use of beta-tubulin sequence as a predictive model of benzimidazole activity is discussed with particular reference to L. infantum.

Towards the eradication of hookworm in an isolated Australian community

Hookworm (Ancylostoma duodenale) and other enteric parasites such as Giardia and Hymenolepis are common in Aboriginal communities in northem Australia, and their presence is associated with iron deficiency, anaemia, and failure to thrive. We report the outcome of a sustained, community-based control programme that used regular albendazole in one isolated community. Whereas hookworm has been effectively controlled by the programme, no sustained effect on the prevalence of Giardia and Hymenolepis was seen; the control of these parasites will depend on improvements in health education. This programme might serve as a model for community-based or population-based drug treatment programmes elsewhere.

In vivo efficacy of albendazole againstGiardia duodenalis in mice

The antigiardial effects of albendazole were demonstrated in vivo using experimental infections ofGiardia duodenalis in mice. These results complement previous in vivo studies in which albendazole was shown to have more potent antigiardial action than the currently applied antigiardial drugs. In mice, 2–4 doses (>100 mg/kg twice daily) were required for complete inhibition of cyst excretion and full elimination of trophozoites from the small intestine. The high doses necessary in mice were not unexpected and are discussed in light of the possible pharmacokinetics of albendazole in the animal model used in this study.