Toxoplasma gondii: How an Amazonian parasite became an Inuit health issue

Toxoplasma gondii is a protozoan parasite that originated in the Amazon. Felids (mammals in the cat family) are the only definitive hosts. These animals shed large numbers of infectious oocysts into the environment, which can subsequently infect many intermediate hosts, including birds, mammals and, possibly, fish. Human T. gondii seroprevalence is high in some parts of the Canadian Arctic and is associated with adverse health consequences among Inuit population. Since the range of felids does not extend to the Arctic, it is not immediately obvious how this parasite got from the Amazon to the Arctic. The objectives of this overview are to summarize the health impacts of T. gondii infection in Inuit in Canada's North and to consider how this infection could have reached them. This article reviews the prevalence of T. gondii infection in terrestrial and marine animals in the Canadian Arctic and discusses their potential role in the foodborne transmission of this parasite to humans. Two distribution factors seem plausible. First, felids in more southern habitats may release infectious oocysts into waterways. As these oocysts remain viable for months, they can be transported northward via rivers and ocean currents and could infect Arctic fish and eventually the marine mammals that prey on the fish. Second, migratory terrestrial and marine intermediate hosts may be responsible for carrying T. gondii tissue cysts to the Arctic, where they may then pass on the infection to carnivores. The most likely source of T. gondii in Inuit is from consumption of traditionally-prepared country foods including meat and organs from intermediate hosts, which may be consumed raw. With climate change, northward migration of felids may increase the prevalence of T. gondii in Arctic wildlife.

Giardia and Cryptosporidium on dairy farms and the role these farms may play in contaminating water sources in Prince Edward Island, Canada

BACKGROUND

Cattle represent a reservoir for Giardia and Cryptosporidium and may contaminate water sources.

OBJECTIVES

To determine the distribution of Cryptosporidium and Giardia on dairy farms and in water bodies near the farms. FARMS AND WATER SOURCES: Twenty dairy farms and 20 wells and 13 surface water samples associated with dairy farms.

METHODS

Proportions of samples positive for Cryptosporidium or Giardia were determined by a direct immunofluorescence assay. Fecal and water samples were taken at different times.

RESULTS

Thirty-two (95% CI: 29-35%) and 14% (95% CI: 12-17%) of fecal samples, and 100 (95% CI: 96-100) and 55% (95% CI: 32-77%) of herds, were positive for Giardia and Cryptosporidium, respectively. Giardia duodenalis assemblage E was detected in high proportions (90%) of fecal samples. Cryptosporidium bovis predominated (51%) in all cattle. C. andersoni predominated in adult cattle (53%), whereas the predominant species in animals < 2 months and 2-6 months was C. bovis, respectively. Only calves < 2 months of age were positive for C. parvum. In 46% (95% CI: 19-75%) and 85% (95% CI: 55-98%) of surface water, concentrations of Giardia cysts and Cryptosporidium oocysts were higher in downstream, than in upstream, locations of farms, whereas only 1 groundwater sample was positive for Cryptosporidium.

CONCLUSIONS

This sample of dairy cattle was predominantly infected with nonzoonotic species and genotypes of Cryptosporidium, Giardia, or both. More studies are needed to determine if the presence of Giardia or Cryptosporidium in surface water was associated with shedding in animals from nearby farms.

Cryptosporidiosis in quails

Cryptosporidial infection was diagnosed in a flock of 4-week-old common quails (Corturnix cortunix). The main gross pathological changes were excess mucus in the trachea, nasal mucosal congestion and shrunken bursa of Fabricius (Bursa cloacalis). Microscopically, the main changes were epithelial deciliation and hyperplasia and inflammatory cell infiltration of the lamina propria in the trachea, bronchi and nasal cavity; epithelial hyperplasia in some oesophageal and salivary glands, and epithelial hyperplasia and follicular atrophy in the bursa. Protozoan parasites attached to the affected epithelium were identified by electron microscopy as Cryptosporidium spp.

Argas persicus sensu stricto does occur in Australia

The status of Argas persicus in Australia has been a matter of controversy for over 25 years. Although early records of A. persicus sensu stricto are common, a major revision of the genus indicated that these records refer to A. robertsi, first described in 1968 from northern Australia, and to an "undescribed" member of the complex occurring in the south. Here, we show that A. persicus sensu stricto does occur in southern Australia and is the only species of Argas in the area recorded from poultry. Another undescribed species belonging to the A. persicus complex, from crows' nests near Lake Eyre in South Australia, was also discovered. This information is of considerable epidemiological significance, as A. persicus sensu stricto is a major vector for a number of highly pathogenic diseases of poultry, not all of which have yet been recorded from Australia.

A simplified method of cleaning ixodid ticks for microscopy

The cleaning of ixodid ticks for microscopy can be achieved quickly and efficiently using a combination of a wax solvent and an ultrasonic cleaner. The technique involves minimum handling of specimens, produces no detectable damage and is suitable for cleaning many specimens at the same time.

Fish- and shellfish--borne trematode infections in Canada

Food-borne trematode infections are endemic in various parts of the world, particularly Southeast Asia. Despite the high prevalence, morbidity and total costs of these infections, they remain poorly recognized by public health authorities and consumers. Factors such as poor sanitation and traditional methods of food preparation hasten the spread of food-borne trematode infections in endemic regions and must be carefully examined in order to develop effective control strategies. There is also a growing risk to consumers in non-endemic countries as a result of international trade. A considerable quantity of freshwater fish and shellfish is imported into Canada from endemic countries in Southeast Asia. Some of these products are imported fresh or processed in such a way that the infective metacercariae may not be destroyed. Further, current inspection procedures in Canada may not detect the presence of all parasites in imported fish products. Therefore, there may be a risk of infection if the fish or shellfish is consumed raw or lightly cooked. Many of the cases of infection in Canada involve recent immigrants from endemic regions who have become infected either before arriving or through the consumption of traditional or ethnic dishes prepared from imported products. International travel and the increasing availability and interest in ethnic foods also contribute to the risk of infection in all Canadians. In addition to these imported trematodes, a number of species are found in freshwater fishes and shellfish in North America and have also caused illness in humans. Although the prevalence of infection remains relatively low in Canada, the need for an increased general awareness of food-borne trematode infections and their causes is indicated.

A comparison of conventional microscopy, immunofluorescence microscopy and flow cytometry in the detection of Giardia lamblia cysts in beaver fecal samples

A variety of domestic and wild animals are considered to be potential sources of giardiasis in humans. As a result, numerous studies have been reported on the prevalence of Giardia lamblia infection in animals. The majority of these surveys have involved various floatation techniques followed by conventional microscopy in order to detect cysts in fecal samples. Immunofluorescence microscopy has become popular in recent years for the detection of G. lamblia cysts in both clinical and environmental samples. This technique can be automated by combining it with flow cytometry. The present study represents a direct comparison of conventional microscopy, immunofluorescence microscopy, and flow cytometry in terms of their relative efficiency in the detection of G. lamblia cysts in beaver fecal samples. As a result of viewer fatigue, or low cyst concentrations, false negatives were common with conventional microscopy, leading to low prevalence estimates. By specifically targeting the cysts, immunofluorescence microscopy provided more reliable results in a shorter time than conventional methods. When flow cytometry was used in combination with immunofluorescence, a larger number of samples could be examined in a relatively short period of time. The results obtained indicated that this technique allowed for more consistent recognition than either conventional or immunofluorescence microscopy of positive samples containing smaller numbers of cysts.

Diphyllobothrium, Anisakis and other fish-borne parasitic zoonoses

Fish-borne parasitic zoonoses such as anisakiasis and diphyllobothriasis occur infrequently in Canada and more work needs to be done on the interactions and transmission dynamics of marine and freshwater anisakids in North America. The diphyllobothriid tapeworms are primarily restricted to the northern Canada. Problems with the specific identification of these parasites from their fish hosts prompted the development of a series of nucleic acid probes. Use of the polymerase chain reaction proved to be quick, accurate and requires little skill, once developed.

Anthelmintic-induced destrobilation and its influence on calculated drug efficacy in Hymenolepis diminuta infections in rats

Anthelmintic efficacy studies typically involve direct counts of worms remaining in the host shortly after drug treatment. Few such studies, however, have considered the phenomenon of tapeworm destrobilation when determining effective dosages. The present study reports on the frequency of drug-induced destrobilation and the subsequent regeneration of Hymenolepis diminuta in rats following treatment with niclosamide or praziquantel and its implications with respect to the apparent efficacy of these anthelmintics. Drug efficacies very similar to those reported in the literature were determined upon examination of infected animals 24 hr posttreatment. Small regenerating worms were, however, observed in the small intestine of rats 8 days after treatment, indicating that destrobilated worms were present, but overlooked, during the initial examination. Within several days posttreatment, destrobilated worms can regenerate to a size that is readily apparent in the gut contents, allowing the effective dosage to be determined with much greater confidence. Due to the demonstrated ability of these destrobilated worms to regenerate to the gravid state, it is imperative that a fully effective anthelmintic dosage be determined and administered.

Caprine arthritis-encephalitis virus infection of goats in South Australia

Caprine arthritis-encephalitis virus (CAEV) infection of dairy goats was shown by virus isolation and serology to be widespread in South Australia. CAEV was isolated at necropsy from 24 of 27 dairy goats with swollen joints from 13 herds, and from 9 of 30 liver dairy goats in 7 herds. Virus was isolated most frequently from synovial membranes, and occasionally from mammary glands, mammary lymph nodes, choroid plexus, lungs, spleen, bone marrow, salivary glands, leucocytes, synovial fluid and milk. Antibody to CAEV was detected in the serum of 13 of 17 of the necropsied goats tested in a single-line gel diffusion test, and in another 3 retested with a modified double-line technique. Serum antibody was also demonstrated in 61 of 77 dairy goat herds, many with histories of arthritis. In 1984 to 1986 the annual number of serologically positive serums and proportions of the numbers tested were 134 (40%), 121 (45%) and 42 (18%), respectively. CAEV was isolated from leucocytes of 8 live goats in 6 of these herds. In fibre goats antibody was detected in the serum of 25 Angora and 19 crossbreds (0.1%) from the 33,279 Angora, 1,705 Cashmere, 8,715 crossbred and 904 feral goats tested.

Ultrastructure of Sarcocystis spp. (Protozoa: Apicomplexa) in rodents from North Sulawesi and West Java, Indonesia

Tissue cysts of the protozoan genus Sarcocystis were detected in the skeletal muscles of 16 (40%) of 40 wild rodents captured in North Sulawesi and West Java, Indonesia. Two types of cysts were found to differ in their morphological characteristics. Macroscopic and microscopic cysts bounded by thick radially-striated cyst walls were detected at both locations in a total of 13 rodents belonging to seven different species (Bunomys chrysocomus, B. fratrorum, Maxomys bartelsii, M. musschenbroekii, Paruromys dominator, Rattus xanthurus and R. exulans). The primary cyst walls contained numerous broad spatula-like protrusions and the cysts were identified as S. singaporensis Zaman and Colley, 1976. In contrast, microscopic cysts bounded by thin smooth cyst walls were detected in seven rodents belonging to three different species captured at Toraut in North Sulawesi (B. chrysocomus, B. fratrorum and P. dominator). Ultrastructural examination revealed numerous slender hair-like protrusions of their primary cyst walls. It is proposed that these cysts be named S. sulawesiensis sp. n. on the basis of their unique morphological characteristics, their intermediate host range and their limited geographic distribution. Mixed infections by both species were found in three rodent species (B. chrysocomus, B. fratrorum and P. dominator).

Sarcocystis mucosa (Blanchard 1885) Labbé 1889 in unadorned rock wallabies (Petrogale assimilis) and Bennett's wallabies (Macropus rufogriseus)

Macroscopic cysts of a protozoan parasite were detected in the gastro-intestinal walls of two unadorned rock wallabies (Petrogale assimilis) and 20 Bennett's wallabies (Macropus rufogriseus). The cysts were located predominantly in the muscularis externa and the submucosa of the forestomach, small intestine and colon and sometimes in the muscularis externa of the oesophagus and caecum. All cysts exhibited similar morphological and ultrastructural characteristics. They were bounded by thick primary cyst walls (containing distinctive bulbous-like protrusions) and were surrounded by collagen fibres and host connective tissue cells (mainly fibrocytes). The cysts were divided by septae into internal compartments containing metrocytes and cystozoites. The cystozoites contained numerous organelles typical of apicomplexan protozoan parasites (including an apical complex, a micropore, rhoptries, micronemes, polysaccharide granules and 22 subpellicular microtubules) and they were observed to divide by the process of endodyogeny. Despite the unusual location of the cysts, they were classified on the basis of their ultrastructural characteristics as Sarcocystis mucosa (Blanchard 1885) Labbé 1889.

The fine structure of the intramitochondrial crystalloids in mitochondrial myopathy

The fine structure of the intramitochondrial crystalloids found in mitochondrial myopathies was investigated using high angle tilting of ultrathin sections and freeze fracture replicas. Observations show the crystalloids to be composed of 8 nm granules in a unique array. Analysis of the arrangement seen in three mutually perpendicular planes has permitted a model of the crystalloid and its relationship to the mitochondrial membranes to be proposed. The biochemical nature and pathophysiological significance of the crystalloids is still undetermined.

Bidirectional differentiation in a large cell pleomorphic primary endocrine carcinoma of the skin (a variant of malignant Merkel cell tumour)

A primary endocrine carcinoma of the skin is described in which the tumour cells showed the unusual features of large size and marked nuclear pleomorphism. Ultrastructural examination revealed combined features of squamous and endocrine differentiation in the same cells, a phenotype which has been previously anticipated but only recently described in endocrine carcinomas of the skin. In addition, immunocytochemical staining showed the co-expression of cytokeratin and neurofilament. The globular masses of cytokeratin corresponded to paranuclear whorls of intermediate filaments and there was also strong and diffuse staining for neuron specific enolase. Many tumour cells stained for calcitonin, VIP, ACTH, and S100 protein. Large tumour cells with markedly pleomorphic nuclei and co-expression of cytokeratin and neurofilament add to the expanding morphological spectrum of primary endocrine carcinomas of the skin.

Morphological and biochemical correlates in the characterization of Sarcocystis spp

Isoenzyme electrophoretic techniques were applied to the characterization of seven Sarcocystis spp. that had been identified by conventional morphological studies. Cystozoites were harvested from macroscopic cysts from sheep, cattle, and mice and from microscopic cysts from sheep, cattle, and goats. Soluble cystozoite extracts were subjected to cellulose acetate gel electrophoresis and characterized at 15 of the 39 enzyme loci examined. Genetic relationships among isolates were examined by simple phenetic clustering. Two different morphological types of macroscopic cysts from sheep, identified as S. gigantea (syn. S. ovifelis) and S. medusiformis, consistently differed at 40% of the loci examined. Such genetic divergence confirms their separate morphotypic classification. Both differed from microscopic cyst isolates from sheep at 87% of the loci examined; however, two different morphotypes of microscopic cysts were found in the sheep sampled (thick-walled and thin-walled cysts). Until sufficient numbers of each type can be isolated and examined separately, both were regarded as belonging to the species S. tenella (syn. S. ovicanis). Macroscopic and microscopic cysts from cattle consistently differed at 80% of the loci thereby supporting their separate classification as S. hirsuta (syn. S. bovifelis) and S. cruzi (syn. S. bovicanis), respectively. Isolates from goats (microscopic cysts identified as S. capracanis) differed from S. tenella and S. cruzi at 20% and 47% of the loci, respectively. All macroscopic cyst isolates from the various host animal species (including S. muris from mice) differed from each other at nearly all loci. Isoenzyme electrophoretic techniques therefore provided genetic evidence supporting the classification of these various Sarcocystis spp. by their morphological characteristics.

The ultrastructural identification of Auer body precursors in a case of acute promyelocytic leukemia using high-angle specimen tilt

Auer body (AB) precursors were identified in a case of poorly differentiated acute promyelocytic leukemia (APL). They consist of azurophilic granules containing membraneous lamellae. In most granules the lamellae were seen only after high-angle specimen tilting. In small but more mature ABs, the periodic tubular structure also was visualized best by specimen tilting. An intermediate granule having both lamellae and tubules is described and discussed in relation to the fusion of azurophilic granules to form ABs. The early diagnosis of APL, in the absence of ABs and intravascular coagulation, is assisted by specimen tilting to resolve the lamellae in the azurophilic granules.

The role of electron microscopy and microanalytical techniques in the understanding of the pathophysiology of environmental dusts associated with lung disease

The purpose of this study has been to elucidate the usefulness of TEM/STEM/EDX system in the identification of environmental dust within the interstitial macrophages of the lung. The four cases chosen for this study gave variable history of exposure to occupational "dust". A review of literature with particular reference to clay associated pneumoconiosis has been made. Previous studies have given little prominence to the fate or behaviour of inhaled "dust" particles in the intracellular environment. It is here that it is believed that a TEM/STEM/EDX system has the potential of playing a significant role in promoting our understanding of "dust" associated pneumoconiotic disease of the lung. The results obtained from the three cases demonstrate the presence of clay particles in the form of granules, plates and needles or thin flakes within the phagosomes of the interstitial macrophages. On morphological grounds the thin needles or flakes appeared to undergo a process of stacking within the phagosomal matrix resulting in the formation of large closely stacked needle-like structures which lie free in the cytoplasm. The possibility of a physicochemical basis for such a morphological sequence is discussed. The fourth case, that of stainless steel associated pneumoconiosis, also showed evidence of breakdown of the original dust in the macrophages. From the evidence presented it is concluded that application of the TEM/STEM/EDX technique may advance our knowledge of the interaction of inhaled dust and the macrophages at the subcellular level.