Parasitology
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Individual and combined effects of cadmium and 3,3,4,4,5-pentachlorobiphenyl (PCB 126) on the humoral immune response in European eel (Anguilla anguilla) experimentally infected with larvae of Anguillicola crassus (Nematoda)
Parasitology - Tập 128 Số 4 - Trang 445-454 - 2004
Studies on the transmission and course of infection of a Kenyan strain of <i>Theileria mutans</i> Summary Theileria mutans (Aitong) isolated from cattle exposed in the Narok District of Kenya and blood-passaged through cattle 8 times, appeared to have lost its original pathogenicity for cattle. It was demonstrated that the parasite was trans-stadially transmissible by the tick Amblyomma variegatum but not by Rhipicephalus appendiculatus . Four tick–bovine passages were made using A. variegatum , and infective parasites were also harvested from A. variegatum nymphs which had been fed for 5 days on rabbits. Blood containing piroplasms, or lymphoid cells infected with schizonts taken from cattle, at the 2nd tick–bovine passage were shown to be infective on inoculation.The course of the T. mutans infections in the cattle was studied. In tick-induced infections macroschizonts occurred transiently, persisting longest in circulating lymphoid cells. Microschizonts were rarely detected. The macroschizonts were morphologically distinct from those of other Theileria species described from East Africa. In tick-induced infections, the piroplasm parasitaemia increased rapidly and there was evidence of restored pathogenicity of the parasite since high piroplasm parasitaemias were associated with a marked anaemia.
Parasitology - Tập 76 Số 1 - Trang 99-115 - 1978
Human fascioliasis infection sources, their diversity, incidence factors, analytical methods and prevention measures Abstract Human fascioliasis infection sources are analysed for the first time in front of the new worldwide scenario of this disease. These infection sources include foods, water and combinations of both. Ingestion of freshwater wild plants is the main source, with watercress and secondarily other vegetables involved. The problem of vegetables sold in uncontrolled urban markets is discussed. Distinction between infection sources by freshwater cultivated plants, terrestrial wild plants, and terrestrial cultivated plants is made. The risks by traditional local dishes made from sylvatic plants and raw liver ingestion are considered. Drinking of contaminated water, beverages and juices, ingestion of dishes and soups and washing of vegetables, fruits, tubercles and kitchen utensils with contaminated water are increasingly involved. Three methods to assess infection sources are noted: detection of metacercariae attached to plants or floating in freshwater, anamnesis in individual patients, and questionnaire surveys in endemic areas. The infectivity of metacercariae is reviewed both under field conditions and experimentally under the effects of physicochemical agents. Individual and general preventive measures appear to be more complicated than those considered in the past. The high diversity of infection sources and their heterogeneity in different countries underlie the large epidemiological heterogeneity of human fascioliasis throughout.
Parasitology - Tập 145 Số 13 - Trang 1665-1699 - 2018
On the invasion of the central nervous system by nematodes: II. Invasion of the nervous system in ascariasis 1. Experimental infections in mice showed that the larvae ofToxocara canis, T. mystax, Ascaris devosi, A. columnaris andToxascaris transfuga reached the brain of mice; the larvae ofAscaris lumbricoides, A. suum, Parascaris equorum andToxascaris leonina were not recovered from the brain. The larvae ofT. canis, T. mystax, T. transfuga andA. columnaris remained hi the brain of mice for several months. 2. Larvae reaching the brain produced characteristic haemorrhages on the surface of the cerebral hemispheres in the early stages of infection. It was concluded that the larvae reach the brain via the arterial blood stream, leave the arteries at the point where their diameter approximates that of the larvae, i.e. mostly on the surface of the brain, and penetrate into the brain from the subarachnoid space and chorioidal tissues. 3. The larvae ofT. canis were found to occur in the brain of mice in relatively greater numbers than the larvae of other species, but only very rarely caused nervous symptoms. The larvae ofT. canis andT. mystax showed no growth in the brain. 4. The larvae ofA. columnaris (skunk) frequently caused nervous symptoms in mice, the effect appeared to result from traumatic damage due to the relatively large size attained by these larvae about 3 weeks after infection. 5. The brain of infected mice showed very slight changes consequent upon infection with larvae ofT. canis . These larvae moved actively through the tissues; they incited little or no cellular reaction, but left haemorrhagic tracks. The larvae ofA. columnaris also moved actively; when in the extended state they were usually found in normal tissue; when coiled, they were often associated with a necrotic focus infiltrated with leucocytes. 6. After experimental infections of dogs with larvae ofT. canis , two out of twelve infected animals harboured larvae in the brain. No natural infections with these larvae were found in the brains of dogs and cats. After experimental infection, larvae ofT. canis were found in the brain of mice, rats and guinea-pigs, but not of rabbits. 7. Larvae ofA. suum were recovered from the cerebrum of one pig suffering from posterior paralysis, but not in an experimentally infected pig. 8. No larvae ofP. equorum were found in the brain of foals in natural and experimental infections.
Parasitology - Tập 45 Số 1-2 - Trang 41-55 - 1955
On the invasion of the central nervous system by nematodes I. The Incidence and pathological significance of nematodes in the central nervous system A wide variety of nematode species have been observed to invade the central nervous system. They may be located in the meningeal spaces or may penetrate into the tissues of the brain and spinal cord. The pathological changes resulting from invasion of the central nervous system are influenced by the route of entry, the size and the mobility of the parasite. They may be diffuse or focal and may include haemorrhage, degenerative changes, cellular infiltration and glial proliferation. Such changes may or may not be observed in close association with the parasite. Symptoms indicating involvement of the central nervous system have long been associated with nematode infections outside the central nervous system. The pathogenesis of these symptoms is obscure, but they may possibly be of allergic origin. The direct pathological effects on the central nervous system are mainly the result of trauma and are directly proportional to the size and activity of the parasite. The possibility that nematodes may transport viruses into the central nervous system is briefly discussed.
Parasitology - Tập 45 Số 1-2 - Trang 31-40 - 1955
The phylogeny of the Schistosomatidae based on three genes with emphasis on the interrelationships of <i>Schistosoma</i> Weinland, 1858 Schistosomes are digenean flukes, parasitic of birds, mammals and crocodiles. The family Schistosomatidae contains species of considerable medical and veterinary importance, which cause the disease schistosomiasis. Previous studies, both morphological and molecular, which have provided a good deal of information on the phylogenetics of this group, have been limited in the number of species investigated or the type or extent of molecular data used. This paper presents the most comprehensive phylogeny to date, based on the sequences of 3 genes, complete ribosomal small subunit rRNA and large ribosomal subunit rRNA, and mitochondrial cytochrome oxidase 1, sequenced from 30 taxa including at least 1 representative from 10 of the 13 known genera of the Schistosomatidae and 17 of the 20 recognized Schistosoma species. The phylogeny is examined using morphological characters, intermediate and definitive host associations and biogeography. Theories as to the origins and spread of Schistosoma are also explored. The principal findings are that Ornithobilharzia and Austrobilharzia form a sister group to the Schistosoma ; mammalian schistosomes appear paraphyletic and 2 Trichobilharzia species, T. ocellata and T. szidati , seem to be synonymous. The position of Orientobilharzia within the Schistosoma is confirmed, as is an Asian origin for the Schistosoma , followed by subsequent dispersal through India and Africa.
Parasitology - Tập 126 Số 3 - Trang 203-224 - 2003
Observations on the development of<i>Toxocara canis</i>(Werner, 1782) in the dog 1. Evidence from previous literature shows that puppies are commonly infected with larvae ofToxocara canis at birth and that prenatal infection can be produced by feeding embryonated eggs to pregnant bitches. 2. Observations on fifty-eight dogs in Brisbane showed that all of twenty-nine puppies 1–6 months old were infected, while only three out of twenty-nine dogs over 6 months old were infected. 3. In naturally infected puppies, 1–3 weeks old, it was found that at birth third-stage larvae were present in the lungs. Third-stage larvae continued to appear in the lungs for the first week of life; their length was 0·6–1·3 mm. 4. Third-stage larvae were found in the stomach on the day after birth; at 3 days after birth fourth-stage larvae were found in the intestine. 5. It appeared likely that the second moult occurs in puppies before birth, and that the third moult takes place at a length of 1·0–1·3 mm. in the lungs and stomach within the first week of life. 6. By the beginning of the second week, fourth-stage larvae were fully grown and had commenced the fourth moult at a length of 5–7 mm. 7. Throughout the second and third weeks, adults grew rapidly, reaching a length of about 67 mm. by the end of the third week, but no eggs had appeared in the faeces at this time. 8. Experimental infection of mice with eggs showed that the larvae were distributed to the somatic tissues, few reaching the alimentary tract. The larvae did not progress beyond the second stage in the tissues of mice. 9. Experimental infection of dogs with eggs showed that in dogs over 5 weeks old the larvae were distributed to the somatic tissues and did not reach the alimentary tract. The larvae did not progress beyond the second stage, though some of them showed signs of commencing the second moult. In contrast, 1 to 3-week-old puppies infected in the same way were found to harbour larvae in the alimentary tract. Though some of these larvae were probably derived from a naturally acquired prenatal infection, it was evident from the progress of development that the experimental infection resulted in the presence of second-stage larvae in the liver and lungs and that these larvae underwent the second moult, commenced development as third-stage larvae in the lungs, migrated into the stomach and developed to the adult stage in the intestine. 10. Experimental infection of dogs and foxes with mice harbouring second-stage larvae in the tissues showed that, in some instances, development of larvae proceeded in the alimentary tract. No evidence of somatic migration was found in dogs infected in this way, but in foxes second-stage larvae were found in the lungs. 11. The structure and development of the second, third and fourth stage is described in detail and found to resemble closely the development ofT. cati larvae (Sprent, 1956). Second-stage larvae from dog tissues had a length of 0·34–0·44 mm. and the second moult occurred at a length of 0·37–0·44 mm. Third-stage larvae varied in length from 0·46 to 1·36 mm., and the third moult occurred at a length of 0·98–1·3 mm. Fourth-stage larvae measured 1·2–6·3 mm., though moulting fourth-stage larvae were observed up to a length of 7·4 mm. Sexual differentiation occurred during the fourth stage and was evident at a length of about 1·5 mm. 12. The migratory behaviour of the larvae ofT. canis andT. cati is compared and discussed in relation to their wide range of hosts. It is concluded that differences in migratory behaviour are adaptations to prevailing modes of nutrition and it is suggested that the somatic migration occurring in dogs is an adaptation to the non-predatory habits of this particular host.
Parasitology - Tập 48 Số 1-2 - Trang 184-209 - 1958
Evaluation of anthelmintic properties of some plants used as livestock dewormers against Haemonchus contortus infections in sheep
Parasitology - Tập 129 Số 2 - Trang 245-253 - 2004
Migration of the schistosomula of<i>Schistosoma mansoni</i>in mice vaccinated with radiation-attenuated cercariae, and normal mice: an attempt to identify the timing and site of parasite death SUMMARY The migration of the schistosomula ofSchistosoma mansoni labelled with [75 Se] has been followed from the skin to the hepatic portal system. Parasites were detected in all mouse tissues by compressed organ autoradiography. Two separate experiments were performed to track parasites in normal mice, and in mice previously vaccinated with irradiated cercariae. In normal mice, the profile of numbers of autoradiographic foci detected in the skin, lungs, systemic and splanchnic organs was described with time post-infection. The distribution of parasites to systemic organs, following exit from the lungs, paralleled the fractional distribution of cardiac output. Accumulation of schistosomula in the hepatic portal system was complete by day 21 post-infection. Only 2–3 passes of parasites around the vascular system would be required to produce the hepatic portal population. No significant decline in total foci was detected in the first 12 days post-infection. The majority of parasite elimination appeared to occur in the lungs as late as day 21, with lesser proportions in the systemic organs and skin infection site. The pattern of migration in vaccinated mice was similar to that in normal animals. One difference observed was the longer duration of stay in the skin; however, the majority of parasites eventually reached the lungs. The systemic phase of migration occurred on a reduced scale, as did accumulation of parasites in the hepatic portal system. The decline in total foci in vaccinated mice commenced approximately 7 days earlier than in normal mice and proceeded to a lower end-point. Again the majority of parasite elimination appeared to occur in the lungs with lesser proportions in the systemic organs and skin infection site. It is suggested that resistance to reinfection in vaccinated mice has two additive components which combine to retard the migration of schistosomula within the vasculature, preventing them from reaching the hepatic portal system.
Parasitology - Tập 92 Số 1 - Trang 101-116 - 1986
Neurosecretory granules in the infective stage of <i>Haemonchus contortus</i> Large numbers of electron-dense bodies, 700–1900 Å in diameter, usually seen each with its own limiting membrane, were found in axons of the ventral nerve of infective juveniles of H. contortus . Axons containing these granules merged, without limiting membranes, with a ‘light’, diffusely granular region, about 1·5–2 μm3 . The ‘light’ area also merged without boundaries with the underlying cuticle which was different from the surrounding cuticle. This modified cuticle, of which the anterior border lies about 1·3 μm from the posterior edge of the excretory pore, extends slightly beyond the ‘light’ area. Otherwise it is a useful topographical marker for the extent of the ‘light’ area. It is considered that the ‘light’ region has a special role in the physiology of the cuticle. I wish to thank Mrs M. Ross for expert technical assistance and Mr R. I. Sommerville for valuable advice. This work was supported by a U.S. Public Health Service Grant, AI 04093–05. The use of the Siemens electron microscope was made possible by a grant from the Australian Research Grants Committee. Financial help from Parke, Davis and Co. (Australia) is also gratefully acknowledged.
Parasitology - Tập 58 Số 3 - Trang 657-662 - 1968
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