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At least 127 records · Page 7Linked to original sources
PubMed1996

Sex ratio characteristics in Ixodes rubicundus (Acari:Ixodidae), the Karoo paralysis tick.

The sex ratio is an important parameter which characterizes the state and dynamics of natural populations of animals. Although ixodid ticks are specialized ectoparasites, most species are bisexual and are characterized by a 1:1 sex ratio for their progeny. In natural populations and even in laboratory colonies, biased sex ratios are often observed. Ixodes rubicundus, the Karoo paralysis tick, parasitizes domestic stock and wild ungulates in South Africa. Adults quest from vegetation, can mate off or on the host and males are seldom parasitic. We hypothesized that the sex ratio for I. rubicundus would be 1:1 when observed directly in the progeny but that it would be strongly biased towards females in samples of parasitic adults. The results mostly supported the hypothesis but it was also shown that unexplained and unpredictable variations can occur. On hosts, females dominated strongly, except on adult angora goats where the sex ratio was biased in favour of the males. This disparity may be related to a greater retention of males in the coarse, curly hair of angora goats compared to the other hosts. Monthly variations in the sex ratios of the tick on hosts are believed to be related to the large fluctuations in sex ratios of questing ticks.

Animals↗
PubMed1978

[The vulnerability of peripheral nerves and the somatic toxin linkage in tick paralysis of chickens, caused by Argas (Persicargas) walkerae (author's transl)].

Investigations on the impulse propagation and the pattern of amplitudes of toxically by Argas (Persicargas) walkerae larvae impaired peripheral nerves were carried out under oxygen saturated and anoxic conditions. It was demonstrated, that the maximum nerve conduction velocities of the isolated N. ischiadicus were slightly lowered in the first carbogenic and anoxic phase, in comparison with normal nerves. After the second incubation the conduction velocities were, however, almost the same or even higher. The survival times of the nerves after anoxic exposure, which were determined by the temporal persistence of the potentials, revealed that this neurophysiological parameter always resulted in a higher value for the damaged nerves after every two anoxic phases. The diseased nerves therefore tolerate anoxia longer and better than do healthy nerves in respect to their excitability and in their function of impulse propagation. From these in vitro investigations it is concluded that the noxious substance responsible for the paralysis is not cell-bound, but circulates humorally. The toxin possesses membranophilic properties, but its somatic linkage is very labile.

Animals↗
PubMed2003

The Australian paralysis tick may be the missing link in the transmission of Hendra virus from bats to horses to humans.

Hendra virus is a new virus of the family Paramyxoviridae. This virus was first detected in Queensland, Australia, in 1994; although, it seems that the virus has infected fruit-eating bats (flying-foxes) for a very long time. At least 2 humans and 15 horses have been killed by this virus since it first emerged as a virus that may infect mammals other than flying-foxes. Hendra virus is thought to have moved from flying-foxes to horses, and then from horses to people. There is a reasonably strong hypothesis for horse-to-human transmission: transmission of virus via nasal discharge, saliva and/or urine. In contrast, there is no strong hypothesis for flying-fox-to-human transmission. I present evidence that the Australian paralysis tick, Ixodes holocyclus, which has apparently only recently become a parasite of flying-foxes, may transmit Hendra virus and perhaps related viruses from flying-foxes to horses and other mammals.

Animals↗
PubMed1967

Tick paralysis.

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Bites and Stings↗
PubMed1994

Vertical migration of adult Ixodes rubicundus, the Karoo paralysis tick (Acari: Ixodidae).

Mortality due to Karoo paralysis amongst livestock is of considerable economic importance in South Africa. Indications are that the extent of vertical migration of adult ticks, to reach questing positions on grasses, is influenced by sudden climatic changes. Such influences as well as selection of questing substrates were investigated under controlled conditions. Vertical migration of adult Ixodes rubicundus on copper rods was determined in a square metal arena within a closed glass container in a room in which temperature and light could be controlled. Significantly more female and male ticks migrated vertically on 1.5 mm diameter rods than on 4.0 mm rods and on 450 mm long rods than on 100 mm rods. More ticks of both sexes migrated vertically at RH > 80% than at RH < 50% and at 12 degrees C than at 21 degrees C. More female than male and more older than younger ticks migrated vertically in all experiments. The results of this study contribute towards an understanding of the epidemiology of Karoo paralysis.

Animals↗
PubMed2005

Tick paralysis.

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Child, Preschool↗
PubMed2005

Prefeeding Dermacentor andersoni (Acari: Ixodidae) on cattle with prior tick exposure may inhibit detection of tick paralysis by using hamster bioassay.

The effect of prefeeding Dermacentor andersoni Stiles on naive and previously challenged cattle before conducting virulence assays by using hamsters was examined. In an initial observational trial, ticks prefed on a previously challenged heifer did not cause paralysis after transfer to hamsters, whereas ticks from the same lot that were prefed on a naive heifer did cause paralysis. Subsequent paired trails were conducted to simultaneously compare paralysis after feeding on naive and previously challenged heifers. In the first trial, prefeeding ticks on a previously challenged heifer did not result in loss of virulence. In a second trial, ticks fed on a previously challenged heifer had greatly diminished virulence after transfer to hamsters. This also occurred in a third trial after the previously challenged animal had two prior exposures to virulent D. andersoni. Weight gains of ticks that did not cause paralysis after transfer to hamsters were higher after feeding on previously challenged cattle, indicating that loss of virulence was not due to failure of ticks to reattach and feed. Ticks gained little weight on paralyzed hamsters due to the reduced time spent feeding on hamsters when paralysis occurred. Results indicate that assaying ticks for virulence requires prefeeding on naive hosts. If these are not available, rabbits, a resistant host, can be used for prefeeding ticks.

Animals↗