Challenges of nematode control in ruminants: focus on latin america

How do antibiotics kill adult filariae – a novel immune-evasion strategy revealed?
R. D. E. Hansen1, A. J. Trees1, G. S. Bah2, U. Hetzel1, C. Martin3, O. Bain3, V. N. Tanya2, B. L. Makepeace1 1University of Liverpool, Liverpool, L69 7ZJ, UK; 2 Institut de Recherche Agricole pour le Développement, Ngaoundéré, BP 65 Adamawa Region, Cameroon; 3Muséum National d’Histoire Naturelle, 75231 Paris Cedex 05, France
There is no safe macrofilaricidal drug available for the mass treatment of River Blindness (caused by Onchocerca
or lymphatic filariasis. Using O. ochengi in cattle, which is phylogenetically, biologically and immunologically closely
related to O. volvulus, we have shown in vivo that tetracycline antibiotics kill adult worms, and trials with doxycycline in humans
by others have recently shown macrofilaricidal action against O. volvulus.
In O. ochengi the macrofilaricidal action is related to the presence of endosymbiotic Wolbachia sp. bacteria, the prolonged
suppression of which leads to eosinophil activation and death of worms. What has not been clear is whether eosinophils are a
cause, or a result, of worm morbidity and death. We have previously shown that melarsomine is macrofilaricidal, but in in vitro
studies, does not selectively act against Wolbachia. We hypothesised that if eosinophil activation was a result of worm death,
cellular changes in the worm nodule would occur following melarsomine treatment and concurrently with oxytetracycline
Methods: Groups of cattle naturally infected with O. ochengi in Cameroon were treated either with oxytetrecycline (OXY) or
Results: In sequential samples ex vivo quantitative analysis of granulocytes showed that only in the OXY group was there a
significant expansion of eosinophil numbers and a significant early peak in degranulating eosinophils associated initially with
viable worms. Eosinophil degranulation was associated with ultra-structural deformities in the OXY group and eosinophils were
seen within worms. Quantitative PCR of RNA transcripts showed that the 16S r RNA : Oo GST1a ratio (a measure of anti –
Wolbachia effect) was significant only in the OXY group, observations supported by immunohistochemical staining for
Wolbachia surface protein. Bovine transcripts for key cytokines involved in neutrophil activation (GRO and IL-8) were
significantly lowered in the OXY group.
Summary/conclusions: These results support the hypothesis that in this nodule-dwelling filarial worm, OXY-associated worm
death is a result partly or wholly of eosinophil activity, and that in untreated worms, Wolbachia confound this by stimulating a
neutrophil – rich cellular environment in which worms survive for many years.


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