Zur Wirkung verschiedener Benzimidazolcarbamate auf somatische Larven von Ancylostoma caninum ERCOLANI 1859 (Ancylostomidae) und Toxocara canis WERNER 1782 (Anisakidae)1

Transmission trials, ITS2-PCR and RAPD-PCR show identity of Toxocara canis isolates from red fox and dog

Toxocara canis isolates from dog and from red fox were compared in transmission trials and with molecular analysis using RAPD-PCR technique and comparison of the ITS2 sequence. After oral infection of bitches with 20,000 embryonated T. canis eggs of vulpine and canine origin, the vertical transmission to pup's was examined. All animals of both groups developed typical clinical symptoms of toxocarosis. The haematological, serological, parasitological and post mortem results showed no differences between both isolates except for the infectivity of T. canis stages in mice where the fox isolate showed a significant higher infectivity than the dog isolate. The RAPD-PCR showed a similarity coefficient of 0.95, similar to the range of intraspecific variation in Toxocara cati and Toxascaris leonina specimens as outgroups. The ITS2 comparison showed a 100% identity between both isolates with no intraspecific variations. Therefore, the study shows that the fox and the dog isolate of T. canis were identical in infectivity, transmission and molecular structure; a host adaptation could not be found and the fox has to be seen as a reservoir for T. canis infections in dogs. Considering the increasing number of foxes in urban areas the importance of helminth control in dogs is stressed.

The efficacy of doramectin on arrested larvae of Ancylostoma caninum in early pregnancy of bitches

The efficacy of doramectin treatment on arrested A. caninum larvae during early pregnancy of bitches was examined. Four bitches were percutaneously infected with 20,000 third-stage larvae of A. caninum on the day of conception and treated subcutaneously with 1 mg doramectin per kg body weight on day 30 of pregnancy. Four infected untreated pregnant bitches served as controls. A single application of dormectin substantially reduced the number of somatic larvae in bitches and the number of intestinal stages in bitches and puppies. However, it did not completely prevent lactogenic transmission of A. caninum larvae because five out of 23 puppies from three litters of the treated bitches harboured adult worms in their intestines, two of them shed eggs with the faeces. Although clinical disease did not occur in puppies from treated bitches the efficacy of the treatment was not satisfactory from an epidemiological point of view. Despite the treatment puppies with patent infections contaminated their environment with high numbers of eggs thus producing an intolerable infection risk for dogs and humans. No fetotoxic side-effects of the early treatment with doramectin were seen.

Evaluation of mebendazole activity on experimental murine toxocariasis by immune complexes determination

The mebendazole action on experimental murine toxocariasis, using different formulations and vehicles, was studied by means of the detection of antibodies and immune complexes by ELISA. After inoculation with 1000 embryonated Toxocara canis eggs, BALB/c mice were submitted to the anthelmintic treatment as follows: group 1 (control without treatment); group 2 (mebendazole (MBZ), Lomper, Steve Laboratories, Barcelona, Spain, suspended in 1% sodium carboxymethylcellulose (CMC) at a dose of 100 mg/kg/day); group 3 (MBZ, pure compound suspended in 1% CMC at a dose of 100 mg/kg/day); group 4 (MBZ, pure compound suspended in water at a dose of 100 mg/kg/day); group 5 (MBZ, pure compound, formulated to a solid dispersion at 10% in polyethylene glycol 6000 (PEG) then dissolved in water at a dose of 100 mg/kg/day); group 6 (MBZ, pure compound, formulated to a solid dispersion at 10% in PEG then dissolved in water at a dose of 50 mg/kg/day); group 7 (MBZ, pure compound, formulated to a solid dispersion at 10% in PEG then dissolved in water at a dose of 25 mg/kg/day). The treatments were administered on days 5-7 post-inoculation (p.i.) inclusive. The dynamics of the production of the specific antibodies for both excretory-secretory (ES) antigen or crude extract showed a similar profile as compared to the control group. In groups 2 and 6, from the beginning of the treatment, values of immune complexes fell rapidly and were undetectable for the remainder of the experiment. Reductions of immune complex levels by the 4th-6th, 2nd-3rd and 2nd-5th weeks p.i. were observed from groups 3, 5 and 7, respectively. In the other groups, similar profiles as compared to the control group were observed in the dynamics of the specific immune complexes. The evaluation of chemotherapy by immunological methods is a valid technique for the efficiency of the treatment without the disadvantages of larval recovery from several digested tissues. Mebendazole, pure compound, formulated to a solid dispersion in PEG, then dissolved in water reduced immune complexes from the beginning of the treatment. The larval immobilization produced by MBZ should entail a reduction in their metabolic activity with a reduction in the production of excretory-secretory substances which are responsible for the formation of immune complexes. The rapid clearance of specific immune complexes together with a total larvae reduction would explain the decrease in specific immune complexes, which detection is a valid technique for monitoring the efficiency of treatment.

Investigations into the efficacy of doramectin on reactivated somatic larvae of Ancylostoma caninum Ercolani 1859 (Ancylostomatidae) in pregnant bitches

The aim of this investigation was to examine whether reactivated somatic Ancylostoma caninum larvae can be eliminated by the administration of doramectin to pregnant bitches. Four pregnant bitches experimentally infected with 20,000 third-stage larvae of A. caninum were treated subcutaneously with 1 mg doramectin per kg body weight on day 55 of the pregnancy (5-8 days before parturition). Another four experimentally infected pregnant bitches served as controls. The single doramectin treatment completely prevented galactogenic infections in the puppies. Neither intestinal stages nor somatic larvae could be found. The administration of doramectin caused no local or generalized side-effects in the bitches. All 16 puppies of the treated bitches were born healthy and remained so during the whole trial period. Beginning during the third week after birth, all 20 puppies of the untreated bitches developed a severe microcytic, hypochromic anaemia. They had to be killed between 17 and 35 days after birth. Post mortem, they revealed a total of 8649 intestinal stages of A. caninum.

[Behavior and pathogenicity of larva of Toxocara canis Werner 1782 (Anisakidae) in the mouse]

To evaluate the interdependence between pathological changes and the level of infection the behaviour of Toxocara canis larvae in the host, the course of the disease as well as quality and quantity of histological changes were investigated after experimental infection with 1,000, 500, 250, and 125 larvae respectively. The main places where the larvae of Toxocara canis were found at any time after infection were musculature and brain. Regardless of the level of infection the absolute and relative number of larvae in the brain increased linearly, and parallel decreased in musculature. After the 60th day post infection the mice infected with 1,000 larvae showed compulsive movements, disturbance of equilibrium and paralysis of the hindlegs. The mice infected with 500 larvae showed similar symptoms 30 to 40 days later. Mice with weaker infections only showed slight disturbances of the general condition at the end of the trials. In the brain of all animals infected with larvae of Toxocara canis inflammatory reactions were found. Severe destructive changes in the nervous substance together with clinical symptoms were seen only in higher infected mice.

[The effect of ivermectin on reactivated somatic larva of Ancylostoma caninum Ercolani 1859 (Ancylostomidae) in the pregnant dog]

It was evaluated by means of a controlled test to what extent reactivated larvae of Ancylostoma caninum were influenced by single or double treatment with ivermectin. The investigations were done with a total of ten experimentally infected bitches. The single treatment of dams two to ten days ante partum with 0.5 mg or 1 mg ivermectin per kg bodyweight reduced the wormburden of their puppies on an average by 96.6% and 98.5%, respectively. The double treatment with 0.5 mg/kg bodyweight ante and post partum each with an interval of ten days completely prevented lactogenic infections with Ancylostoma caninum. Following a single application of 0.5 mg ivermectin per kg bodyweight the excretion of larvae was markedly delayed and remained on a low level. In addition the infections of the puppies of single treated dams became patent on an average 9.5 and 14.5 days later than the controls. In the bitches no side-effects, neither local nor general, were seen after the treatment with ivermectin. All forty puppies of the treated bitches were born without visible damages.