An outbreak of schistosomiasis in Atlantic brant geese, Branta bernicla hrota

Neonatal Care of Anseriformes

Neonatal Anseriformes require specialized care for successful development including access to clean swimming water and food presentation that stimulates natural feeding behavior. Knowledge of natural history is essential for successful rearing. Lightweight and waterproof materials can be used for corrective splinting of many developmental disorders that allow birds to ambulate normally and swim. Captivity-associated lesions can be minimized through proper husbandry and hygiene. Anseriformes are susceptible to a variety of bacterial, viral, fungal, and parasitic diseases, some of which are reportable to state health agencies.

Descriptive Pathological Study of Avian Schistosomes Infection in Whooper Swans (Cygnus cygnus) in Japan

Simple Summary

Avian schistosomes are a group of parasites responsible for most of the reported cases of cercarial dermatitis outbreaks. Among others, Trichobilharzia is considered the largest genus of avian Schistosomatidae, and it infects more than 40 avian species. The present study involves a descriptive pathological study of avian schistosome in 54 whooper swans (Cygnus cygnus) from various rescue/rehabilitation centers in Honshu, Japan. Interestingly, adult schistosomes were detected in the lumen of mesenteric, serosal, portal, and testicular veins, in the capillaries of the intestinal lamina propria, and in the sinusoids of the adrenal gland, spleen, and liver of 23 (42.59%) swans. Schistosomes were assumed to be Allobilharzia visceralis based on the morphological characteristics of the worm and eggs found at histopathological examination of internal organs, along with suggestive pathological findings as well as the pathological findings. Collectively, the present study provides novel descriptive pathological data about schistosome infection in whooper swans with new insights on their role in the transmission and spreading of avian schistosomes in Japan.

Abstract

Cercarial dermatitis, or Swimmer’s itch, is one of the emerging diseases caused by the cercariae of water-borne schistosomes, mainly Trichobilharzia spp. Since the zoonotic potential of Allobilharzia visceralis is still unknown, studies on this schistosome would be helpful to add knowledge on its possible role in causing human infections. In the present study, 54 whooper swans (Cygnus cygnus) from rescue/rehabilitation centers in Honshu, Japan, were necropsied to identify the cause of death. Grossly, 33 (61.11%) swans were severely emaciated and 23 (42.59%) had multiple reddened areas throughout the length of the intestine with no worms detected in the internal organs. Microscopically, adult schistosomes were found in the lumen of the mesenteric, serosal, portal, and testicular veins, in the capillaries of the intestinal lamina propria, and in the sinusoids of the adrenal gland, spleen, and liver of 23 (42.59%) swans. Hypertrophy of veins containing adult worms was identified in 15 (27.77%) swans, and vascular lumen obliteration was observed in 8 (14.81%) swans. Mild to severe villous atrophy and superficial enteritis were observed in 8 birds (14.81%), whereas bile pigments and hemosiderin were detected in the livers of 14 (25.92%) and 18 (33.33%) swans, respectively. In three swans (5.55%), schistosome parasites were found in the subcapsular veins of the testes. The schistosomes in the present study were assumed to be A. visceralis based on the microscopical and histological evidence of adult schistosomes found in the lumen of veins as well as the infection pathology, which was very similar to the schistosome-induced pathology previously reported in swans infected by A. visceralis in Europe and Australia. The swans examined herein most likely died from obstructive phlebitis associated with A. visceralis, but further molecular confirmation is required for identification of this species. However, the present study does not provide new data on the zoonotic potential, but only on the pathogenic potential of this schistosome in swans. Furthermore, our study provides a novel contribution to the description of the pathological effects of avian schistosomes infection in whooper swans in Japan.

Emerging and Re-emerging Diseases of Selected Avian Species

Emerging infections and re-emerging diseases in birds can be caused by numerous factors and need to be recognized and understood. This article introduces and summarizes author-selected emerging and re-emerging diseases of avian species. These diseases hold significance as they relate to scientific research, disease recognition and identification, avian welfare aspects, and ecosystem health. Some are significant in human health and others affect production medicine. These and many others remain important pathogens of worldwide consequence.

Having bird schistosomes in mind-the first detection of Bilharziella polonica (Kowalewski 1895) in the bird neural system

Nasal bird schistosomes can cause bilharziosis in birds and have the potential to cause swimmer's itch in humans. We determined the prevalence of bird schistosomes in 106 mallards (Anas plathyrhynchos) from 11 water sources in Germany from 2014. Dissections were performed focusing on parasitic infections of the neural system. Infections with Trichobilharzia regenti (Horák et al. 1998) were found in 21% of the birds (n = 22), whereas Bilharziella polonica (Kowalewski 1895) were found between the brain membranes (meninges) and the brain, in the spinal cord or in the intestine of 12% of the mallards (n = 13). No significant influence of sex, age, and body condition between infected and non-infected animals was observed. Our study provides the first description of B. polonica from the neural system of birds and provides an epidemiological understanding of a parasite of human health concern.

Obliterative Endophlebitis in Mute Swans (Cygnus olor) Caused by Trichobilharzia sp. (Digenea: Schistosomatidae) Infection

Schistosome infections in mammals cause chronic proliferative vascular lesions associated with the presence of adult parasites in the lumen of mesenteric and portal veins. In birds, however, this has never been reported. In this study, we found obliterative endophlebitis associated with the presence of adult schistosomes ( Trichobilharzia sp., probably Trichobilharzia filiformis) as the main pathologic finding in five of eight mute swans ( Cygnus olor). On histologic examination, the intestinal and portal veins of these swans showed moderate to severe, diffuse, hyperplastic endophlebitis, characterized by myointimal hyperplasia, often with obliteration of the vascular lumen. In addition, moderate to severe lymphocytic and granulocytic enteritis occurred in all eight swans associated with the presence of schistosome eggs in the intestinal mucosa. Other findings included hepatic and splenic hemosiderosis and high hepatic copper levels. The vascular lesions associated with Trichobilharzia sp. infection may have contributed to the emaciation and death of those mute swans by obstruction of venous return in the intestinal and portal veins.

Avian schistosomes and outbreaks of cercarial dermatitis

Cercarial dermatitis (swimmer's itch) is a condition caused by infective larvae (cercariae) of a species-rich group of mammalian and avian schistosomes. Over the last decade, it has been reported in areas that previously had few or no cases of dermatitis and is thus considered an emerging disease. It is obvious that avian schistosomes are responsible for the majority of reported dermatitis outbreaks around the world, and thus they are the primary focus of this review. Although they infect humans, they do not mature and usually die in the skin. Experimental infections of avian schistosomes in mice show that in previously exposed hosts, there is a strong skin immune reaction that kills the schistosome. However, penetration of larvae into naive mice can result in temporary migration from the skin. This is of particular interest because the worms are able to migrate to different organs, for example, the lungs in the case of visceral schistosomes and the central nervous system in the case of nasal schistosomes. The risk of such migration and accompanying disorders needs to be clarified for humans and animals of interest (e.g., dogs). Herein we compiled the most comprehensive review of the diversity, immunology, and epidemiology of avian schistosomes causing cercarial dermatitis.

Final hosts and variability of Trichobilharzia regenti under natural conditions

In Europe, despite of intensive work on avian schistosomes in the past, only one representative of nasal schistosomes has been detected so far, Trichobilharzia regenti, a species that remained undescribed to the scientific community until 1998. Since then, however, T. regenti has gained a considerable attention, not only due to the induction of serious lesions concomitant with the migration of the schistosomulae through the central nervous system of their natural hosts (birds) but also due to their implication in cercarial dermatitis and their neurotrophic behaviour in mammals (mice, experimental) where the parasite migrate to the CNS. From 2001 to 2010, by a parasitic control of various potential final hosts (aquatic birds) living in natural condition in France and in Iceland, we detected T. regenti in six species: Anas platyrhynchos, Cygnus olor, Aythya fuligula, Aythya ferina, Mergus merganser and Anser anser. Although morphological features, mainly of eggs, showed some variations with the original description of the parasite, molecular analysis confirmed their membership to the T. regenti species. Nevertheless, specific molecular and morphological variations were especially observed for nasal parasite isolated from Anas clypeata. For this species, we discuss the possibility for this nasal schistosome to belong to a nasal Trichobilharzia species already described in Africa or even an undescribed nasal species.

Molecular systematics of the avian schistosome genus Trichobilharzia (Trematoda: Schistosomatidae) in North America

Trichobilharzia is a genus of threadlike schistosomes with a cosmopolitan distribution in birds. Species of Trichobilharzia achieve notoriety as major etiological agents of cercarial dermatitis, or swimmer's itch. There are 40 species described in the literature, for which the majority lacks molecular sequence information. To better understand the phylogenetic relationships, diversity, species boundaries, host use, and geographic distribution of this genus better, we surveyed 378 birds and over 10,000 snails from North America. The phylogenetic analysis was based on nuclear 18S, 28S rDNA, internal transcribed spacer region and mitochondrial cytochrome oxidase I sequence data. Specimens were recovered that could be related to 6 of the 14 described species of Trichobilharzia from North America (Trichobilharzia physellae, Trichobilharzia querquedulae, Trichobilharzia szidati, Trichobilharzia stagnicolae, Trichobilharzia franki, and Trichobilharzia brantae). An additional 5 lineages were found that could not be related directly to previously described species. Trichobilharzia brantae, transmitted by Gyraulus parvus, grouped outside the clade containing the recognized species of Trichobilharzia. A subgroup of the Trichobilharzia clade designated Clade Q was comprised of closely related species whose adults and eggs are similar, yet the European species use lymnaeids whereas the North American species use physids as snail hosts. This molecular phylogeny provides a useful framework (1) to facilitate identification of worms, including those involved in dermatitis outbreaks; (2) to test hypotheses about the evolution, diversification, host-parasite interactions and character evolution of Trichobilharzia; and (3) to guide future taxonomic revision of Trichobilharzia.

Avian schistosomes in French aquatic birds: a molecular approach

The prevalence of human cercarial dermatitis (HCD) caused by bird schistosomes appears to be increasing in France, in light of the impact of tourism combined with high densities of wild aquatic hosts in freshwater areas. The present work expands our knowledge of schistosome systematics by including samples of bird schistosomes collected from their natural hosts in France. Heads (318) and viscera (81) of aquatic birds belonging to 16 species from five orders, collecting during the hunting seasons or found dead, were autopsied for nasal and visceral schistosomes. Eggs and/or adults were analysed by molecular methods using the D2 domain and the second internal transcribed spacer (ITS-2) region of rDNA to determine species. Even if nasal eggs were polymorphic according to the host, all haplotypes were similar to that of Trichobilharzia regenti. Marked diversity of visceral species was observed. Final hosts under natural conditions were reported. For the first time, Trichobilharzia franki is reported in its natural bird hosts, Anas platyrhynchos, Anas crecca, Aythya fuligula and Cygnus olor. We also identified T. szidati in A. crecca and Anas clypeata. Bilharziella polonica was found in six species of aquatic birds, including Grus grus. This finding is the first record of bird schistosomes in this aquatic bird. Three new taxa of visceral schistosomes in Anser anser are strongly suspected according to their haplotypes. Futhermore, a new haplotype of visceral schistosomes isolated in Cygnus olor and similar to Allobilharzia visceralis was identified.

Health of herring gulls (Larus argentatus) in relation to breeding location in the early 1990s. II. Cellular and histopathological measures

Organosomatic indices, hematological indicators of stress, and histopathological lesions were quantified for over 150 incubating herring gulls (Larus argentatus) sampled in 11 colonies throughout the Great Lakes and reference colonies in Lake Winnipeg and the Bay of Fundy. Of 21 parameters assessed, significantly more differed between Great Lakes colonies and reference colonies than between the two reference colonies. Relative adrenal, kidney, and liver masses of gulls from some Great Lakes colonies were reduced and thyroid masses increased relative to gulls from reference colonies. Foci of cellular atypia were observed in the hepatocytes of two Great Lakes gulls. Chronic periportal hepatitis, lipogranulomas and vacuolation of hepatocytes, and chronic granulomatous interstitial nephritis were more prevalent or severe in gulls from Great Lakes colonies and were associated with contaminants. The kidneys of gulls from the three most contaminated locations were damaged and functionally compromised. Interstitial nephritis was likely the most functionally significant histopathological lesion. Portal-tract fibrosis, granulomatous hepatitis, and kidney tubule dilation/obstruction and splenic enlargement were more prevalent or severe at reference sites and were associated with blood-borne parasites. Amyloid deposits were observed in the spleen, kidneys, or liver of nearly half of the gulls. Associations between the prevalence or severity of lesions and contaminant levels in gull tissues or the trophic level of their diet suggest some lesions are toxicopathic. Associations were most frequently found with planar halogenated aromatic hydrocarbons and lead. The stress response, as measured by the heterophil/lymphocyte ratio, was attenuated in gulls from Areas of Concern and associated with decreased adrenal mass. Our findings suggest that adult Great Lakes gulls suffered from chronic exposure to chemical stressors in the early 1990s sufficient to modulate endocrine function and physiological processes and induce structural changes in tissues.

Allobilharzia visceralis gen. nov., sp. nov. (Schistosomatidae-Trematoda) from Cygnus cygnus (L.) (Anatidae)

In Iceland, the examination of whooper swans (Cygnus cygnus L.) viscera resulted in the detection of adult digenean flukes of the family Schistosomatidae. The mature worms occurring in the blood vessels of the large intestine and mesenterium caused vascular lesions, around the eggs deposited in the intestinal mucosa and liver granulomatous reactions developed. The morphology of the isolated schistosomes shows certain similarity with the flukes of the genus Trichobilharzia; in males reduced gynecophoral canal, and on both sexes both suckers and spatulate ends are present. However, the Icelandic flukes possess other morphological features which are distinct from the genus: the point of caecal reunion in males takes place posterior to gynecophoral canal and the genital pore is behind acetabulum and anterior to caecal reunion. In order to evaluate the identity of Icelandic schistosomes, sequencing of ITS region of DNA was performed, and the obtained sequence was deposited in GenBank under the accession no. DQ067561. Following phylogenetic analysis of relationship between the sequence of Icelandic flukes and database sequences of other bird schistosome genera (Trichobilharzia, Gigantobilharzia and Dendritobilharzia) showed different position of Icelandic worms in the phylogenetic tree. In conclusion, our study revealed new genus and species of schistosome flukes--Allobilharzia visceralis gen. et sp. n.

Molluscan and vertebrate immune responses to bird schistosomes

There is a growing understanding of risks posed by human contact with the cercariae of bird schistosomes. In general, there are no fundamental biological differences between human and bird schistosomes in terms of their interactions with snail and vertebrate hosts. The penetration of host surfaces is accompanied by the release of penetration gland products and the shedding of highly antigenic surface components (miracidial ciliated plates and cercarial glycocalyx) which trigger host immune reactions. New surface structures are formed during transformation: the tegument of mother sporocysts and the tegumental double membrane of schistosomula. These surfaces apparently serve as protection against the host immune response. Certain parasite excretory-secretory products may contribute to immunosuppression or, on the other hand, stimulation of host immune reactions. Discovery of new species and their life cycles, the characterization of host-parasite interactions (including at the molecular level), the determination of parasite pathogenicity towards the host, the development of tools for differential diagnosis and the application of protective measures are all topical research streams of the future. Regularly updated information on bird schistosomes and cercarial dermatitis can be found at http://www.schistosomes.cz (web pages of Schistosome Group Prague).

Biology of the schistosome genus Trichobilharzia

Trichobilharzia is the largest genus within the family Schistosomatidae, covering over 40 species of avian parasites. To clarify the existing confusion in the systematics of the genus, we recommend combining knowledge of life cycles and developmental stages, snail/bird hosts, cytogenetical and molecular data together with morphological criteria for the characterization of particular species. The high specificity of Trichobilharzia for the intermediate host is a likely reflection of the ability to avoid the internal defence of specific snails. The spectrum of final hosts (birds) seems to be much wider. The infection of birds--trichobilharziasis--may lead to considerable tissue injuries, caused by eggs of the parasite or migration of immature/mature worms through the body. Most Trichobilharzia (visceral species) migrate through the viscera of the host, but nasal species display a neurotropic mode of migration. Due to a low specificity of penetrating cercariae, mammals (including humans) can be attacked. This leads to cercarial dermatitis, predominantly in sensitized hosts. Experimental infections indicate that Trichobilharzia never mature in an incompatible (mammalian) host. However, not all cercariae and schistosomula are necessarily trapped and eliminated in the skin, and parasites may migrate throughout the viscera and the nervous system of mammals. These findings suggest that the pathogenicity of Trichobilharzia may have been underestimated in the past and health risks associated with trichobilharziasis need to be studied further.