Toxocara encephalitis presenting with autonomous nervous system involvement.

Human toxocariasis has been reported to cause a broad spectrum of neurological syndromes, including encephalitis, meningitis and meningo-radiculitis. Nevertheless, cerebral infection by Toxocara may go undiagnosed due to its rarity, elusive symptoms and lack of availability of appropriate testing. We report the case of a 54-year-old man who presented with abdominal pain and paralytic ileus approximately 3 weeks after having eaten raw snails (a folk remedy for peptic ulcer). Three weeks later, marked eosinophilia ensued, associated with mental clouding, nystagmus, diplopia, peripheral limbs ataxia, urinary retention, slackened deep tendon reflexes, arthralgias and myalgias. Cerebrospinal fluid (CSF) examination demonstrated an eosinophilic meningitis, and Toxocara canis cerebral infection was diagnosed by positive serology and by the detection of T. canis DNA in the CSF. The patient made a full recovery following treatment with albendazole and corticosteroids. Physicians should be aware of this rare presentation of toxocariasis, whose diagnosis is, today, facilitated by molecular biology techniques. A history of ingestion of raw snails may alert the clinician to consider the possibility of such an uncommon condition.

Toxocara canis: molecular cloning, characterization, expression and comparison of the kinetics of cDNA-derived arginine kinase.

Arginine kinase (AK) is a member of a highly conserved family of phosphagen kinases. We determined the cDNA sequence of Toxocara canis AK, cloned it in pMAL plasmid and expressed it in Escherichia coli as a fusion protein with maltose-binding protein. The protein has a theoretical molecular mass of 45,376 Da and an estimated isoelectric point (pI) of 8.38. Alignment of the cDNA-derived amino acid sequence of T. canis AK with other phosphagen kinase sequences showed high amino acid identity with other nematode AKs, and phylogenetic analysis placed it as a distinct branch within a nematode AK cluster. Analysis of the N-terminus sequence of T. canis AK revealed the presence of a signal targeting peptide presumably targeting this protein to cytosol or endoplasmic reticulum (ER). T. canis AK showed high activity for l-arginine. The kinetic constants (K(m) = 0.12 mM, K(cat) = 29.18, and K(d) = 0.23 mM) and V(max) (43.76 micromolPi/min/mg protein) of T. canis recombinant-AK were determined for the forward reaction. It also exhibited a synergism for substrate binding (K(d)(Arg)/K(m)(Arg)=1.96). Comparison of K(cat)/K(m)(Arg) values in various arginine kinases indicates that T. canis AK has a high catalytic efficiency (248.19s(-1)mM(-1)). The present study contains the first description of arginine kinase in a zoonotic nematode. The determination of T. canis AK and its phosphagen biosynthetic pathway, which is completely different from those in mammalian host tissues, suggests this enzyme as a possible novel chemotherapy target for VLM syndrome in humans.

A novel C-type lectin secreted by a tissue-dwelling parasitic nematode.

Many parasitic nematodes live for surprisingly long periods in the tissues of their hosts, implying sophisticated mechanisms for evading the host immune system. The nematode Toxocara canis survives for years in mammalian tissues, and when cultivated in vitro, secretes antigens such as TES-32. From the peptide sequence, we cloned TES-32 cDNA, which encodes a 219 amino-acid protein that has a domain characteristic of host calcium-dependent (C-type) lectins, a family of proteins associated with immune defence. Homology modelling predicted that TES-32 bears remarkable structural similarity to mammalian immune-system lectins. Native TES-32 acted as a functional lectin in affinity chromatography. Unusually, it bound both mannose- and galactose-type monosaccharides, a pattern precluded in mammalian lectins by a constraining loop adjacent to the carbohydrate-binding site. In TES-32, this loop appeared to be less obtrusive, permitting a broader range of ligand binding. The similarity of TES-32 to host immune cell receptors suggests a hitherto unsuspected strategy for parasite immune evasion.