RNAscope in situ hybridization reveals microvascular sequestration of Plasmodium relictum pSGS1 blood stages but absence of exo-erythrocytic dormant stages during latent infection of Serinus canaria

BACKGROUND

Birds chronically infected with avian malaria parasites often show relapses of parasitaemia after latent stages marked by absence of parasites in the peripheral circulation. These relapses are assumed to result from the activation of dormant exo-erythrocytic stages produced during secondary (post-erythrocytic) merogony of avian Plasmodium spp. Yet, there is no morphological proof of persistent or dormant tissue stages in the avian host during latent infections. This study investigated persistence of Plasmodium relictum pSGS1 in birds with latent infections during winter, with the goal to detect presumed persisting tissue stages using a highly sensitive RNAscope® in situ hybridization technology.

METHODS

Fourteen domestic canaries were infected with P. relictum pSGS1 by blood-inoculation in spring, and blood films examined during the first 4 months post infection, and during winter and spring of the following year. After parasitaemia was no longer detectable, half of the birds were dissected, and tissue samples investigated for persisting tissue stages using RNAscope ISH and histology. The remaining birds were blood-checked and dissected after re-appearance of parasitaemia, and their tissues equally examined.

RESULTS

Systematic examination of tissues showed no exo-erythrocytic stages in birds exhibiting latent infections by blood-film microscopy, indicating absence of dormant tissue stages in P. relictum pSGS1-infected canaries. Instead, RNAscope ISH revealed rare P. relictum blood stages in capillaries of various tissues and organs, demonstrating persistence of the parasites in the microvasculature. Birds examined after re-appearance of parasitemia showed higher numbers of P. relictum blood stages in both capillaries and larger blood vessels, indicating replication during early spring and re-appearance in the peripheral circulation.

CONCLUSIONS

The findings suggest that persistence of P. relictum pSGS1 during latent infection is mediated by continuous low-level erythrocytic merogony and possibly tissue sequestration of infected blood cells. Re-appearance of parasitaemia in spring seems to result from increased erythrocytic merogony, therefore representing recrudescence and not relapse in blood-inoculated canaries. Further, the study highlights strengths and limitations of the RNAscope ISH technology for the detection of rare parasite stages in tissues, providing directions for future research on persistence and tissue sequestration of avian malaria and related haemosporidian parasites.

A survey of parasitic infections in Psittaciformes and Passeriformes in Mashhad, Iran

The health, growth and fertility of avian species can be negatively affected by parasite infection. This survey assesses the presence, variety and distribution of internal and external parasites among parrots and perching birds in Mashhad, Iran. This study examined 751 caged pet birds from different species and regions in Mashhad for faecal samples and 132 oral swabs for digestive tract parasites. Furthermore, skin scrapings were conducted on 14 canaries displaying dishevelled feathers. During the study, mortalities and moribund birds that had been referred underwent necropsies to examine internal parasites. Following the formol ether faecal examination, only one Malango parrot tested positive for Heterakoidea eggs among 751 faecal samples (0.13%). Further, one cockatiel showed evidence of parasitic infection with Eimeria spp. (0.13%). However, neither Cryptosporidium nor Giardia protozoa were detected in the samples (0%). Oral swabs revealed no evidence of Trichomonas (0%). On the other hand, skin scraping revealed the presence of the mite Dermanyssus in 7 out of 14 canaries with dishevelled feathers (50%). Of 25 moribund and weak budgerigars, 2 were infected with Acuaria in their proventriculus (8%). In addition, 3 out of 14 deceased myna birds carried the nematode Diplotriana in their coelomic cavities (21.42%). In conclusion, the rate of internal parasites has been relatively low in ornamental birds of Mashhad, whereas the prevalence of external parasites has been higher.

Different distribution of malaria parasite in left and right extremities of vertebrate hosts translates into differences in parasite transmission

Malaria, a vector-borne disease caused by Plasmodium spp., remains a major global cause of mortality. Optimization of disease control strategies requires a thorough understanding of the processes underlying parasite transmission. While the number of transmissible stages (gametocytes) of Plasmodium in blood is frequently used as an indicator of host-to-mosquito transmission potential, this relationship is not always clear. Significant effort has been made in developing molecular tools that improve gametocyte density estimation and therefore prediction of mosquito infection rates. However a significant level of uncertainty around estimates remains. The weakness in the relationship between gametocyte burden, measured from a blood sample, and the mosquito infection rate could be explained by a non-homogeneous distribution of gametocytes in the bloodstream. The estimated gametocyte density would then only be a single snapshot that does not reflect the host infectivity. This aspect of Plasmodium infection, however, remains largely neglected. In both humans and birds, we found here that the gametocyte densities differed depending on which side of the body the sample was taken, suggesting that gametocytes are not homogeneously distributed within the vertebrate host. We observed a fluctuating asymmetry, in other words, the extremity of the body with the highest density of parasites is not always the same from one individual to another. An estimation of gametocyte density from only one blood sample, as is commonly measured, could, therefore, over- or underestimated the infectivity of gametocyte carriers. This might have important consequences on the epidemiology of the disease since we show that this variation influences host-to-mosquito transmission. Vectors fed on the least infected body part had a lower parasite burden than those fed on the most infected part. The heterogeneous distribution of gametocytes in bloodstream should be considered to improve diagnosis and test new malaria control strategies.

Trichomonosis outbreak in a flock of canaries (Serinus canaria f. domestica) caused by a finch epidemic strain of Trichomonas gallinae

In the present paper, an outbreak of trichomonosis in a flock of 15 breeding pairs of canaries is described. Trichomonosis was diagnosed on characteristic clinical signs, microscopic examination of crop/esophageal swabs, gross pathology and histopathology. Trichomonads were successfully grown in culture media and were characterized by multi-locus sequence typing. The three genomic loci ITS1-5.8S-ITS2, 18S rRNA and Fe-hydrogenase were analyzed. Molecular characterization confirmed the finch trichomonosis strain, identical to the strain that caused emerging disease in free-living passerine birds in Europe. Flock treatment with metronidazole (200mg/L) in drinking water for 5days was partially effective. After individual treatment with oral application of metronidazole (20mg/kg SID) for 5days no further clinical signs were observed in the flock over next 30 months.

The Strategy to Survive Primary Malaria Infection: An Experimental Study on Behavioural Changes in Parasitized Birds

Avian malaria parasites (Haemosporida, Plasmodium) are of cosmopolitan distribution, and they have a significant impact on vertebrate host fitness. Experimental studies show that high parasitemia often develops during primary malaria infections. However, field studies only occasionally reveal high parasitemia in free-living birds sampled using the traditional methods of mist-netting or trapping, and light chronic infections predominate. The reason for this discrepancy between field observation and experimental data remains insufficiently understood. Since mist-netting is a passive capture method, two main parameters determine its success in sampling infected birds in wildlife, i. e. the presence of parasitized birds at a study site and their mobility. In other words, the trapping probability depends on the survival rate of birds and their locomotor activity during infection. Here we test (1) the mortality rate of wild birds infected with Plasmodium relictum (the lineage pSGS1), (2) the changes in their behaviour during presence of an aerial predator, and (3) the changes in their locomotor activity at the stage of high primary parasitemia.We show that some behavioural features which might affect a bird's survival during a predator attack (time of reaction, speed of flush flight and take off angle) did not change significantly during primary infection. However, the locomotor activity of infected birds was almost halved compared to control (non-infected) birds during the peak of parasitemia. We report (1) the markedly reduced mobility and (2) the 20% mortality rate caused by P. relictum and conclude that these factors are responsible for the underrepresentation of birds in mist nets and traps during the stage of high primary parasitemia in wildlife. This study indicates that the widespread parasite, P. relictum (pSGS1) influences the behaviour of birds during primary parasitemia. Experimental studies combined with field observations are needed to better understand the mechanisms of pathogenicity of avian malaria parasites and their influence on bird populations.

Chlamydia psittaci infection in canaries heavily infested by Dermanyssus gallinae

Dermanyssus gallinae is a haematophagous ectoparasite responsible for anemia, weight loss, dermatitis and a decrease in egg production. Dermanyssus gallinae may play a role in the modulation of the host immune system, maybe predisposing the host to some bacterial infections such as chlamydiosis. This is an important zoonosis. Humans are exposed to Chlamydia psittaci through inhalation of the agent dispersed from the infected birds. In this study, a syndrome observed in an aviary of canaries was investigated. A heavy infestation by D. gallinae was reported. Simultaneously, a C. psittaci infection was molecularly confirmed in the canaries. Combined therapy was applied successfully. The association of C. psittaci with the examined mites has been confirmed. Therefore, we think that D. gallinae have played a role in the spreading of C. psittaci infection among the canaries. Moreover, D. gallinae could have played an important role predisposing the canaries to the development of chlamydiosis, by inducing anemia and debilitation. The control of mites in the aviaries may represent a crucial step for the prevention of important infection such as chlamydiosis in birds and humans.

Effect of repeated exposure to Plasmodium relictum (lineage SGS1) on infection dynamics in domestic canaries

Parasites are known to exert strong selection pressures on their hosts and, as such, favour the evolution of defence mechanisms. The negative impact of parasites on their host can have substantial consequences in terms of population persistence and the epidemiology of the infection. In natural populations, however, it is difficult to assess the cost of infection while controlling for other potentially confounding factors. For instance, individuals are repeatedly exposed to a variety of parasite strains, some of which can elicit immunological memory, further protecting the host from subsequent infections. Cost of infection is, therefore, expected to be particularly strong for primary infections and to decrease for individuals surviving the first infectious episode that are re-exposed to the pathogen. We tested this hypothesis experimentally using avian malaria parasites (Plasmodium relictum-lineage SGS1) and domestic canaries (Serinus canaria) as a model. Hosts were infected with a controlled dose of P. relictum as a primary infection and control birds were injected with non-infected blood. The changes in haematocrit and body mass were monitored during a 20 day period. A protein of the acute phase response (haptoglobin) was assessed as a marker of the inflammatory response mounted in response to the infection. Parasite intensity was also monitored. Surviving birds were then re-infected 37 days post primary infection. In agreement with the predictions, we found that primary infected birds paid a substantially higher cost in terms of infection-induced reduction in haematocrit compared with re-exposed birds. After the secondary infection, re-exposed hosts were also able to clear the infection at a faster rate than after the primary infection. These results have potential consequences for the epidemiology of avian malaria, since birds re-exposed to the pathogen can maintain parasitemia with low fitness costs, allowing the persistence of the pathogen within the host population.

[Investigation of the prevalence of gastrointestinal parasites in aviary birds in homes in the Van province]

This study was conducted to investigate the prevalence of gastrointestinal parasites in aviary birds in the Van province. For this purpose, fecal samples were collected from aviary birds (6 parrots, 5 nightingales, 24 canaries and 35 lovebirds) in Van. In the parasitology laboratory, seventy fecal samples were examined using the native and sedimentation technique for helminth eggs, Eimeria sp. oocysts and Giardia sp. cysts. The same samples were examined by modified-acid-fast staining for Cryptosporidium sp. oocysts. Prevalence of gastrointestinal parasites was found to be 8.57% (6/70) in Van. Eimeria sp. oocysts were detected in lovebird (8.57%) and canaries (8.33%). Cryptosporidium sp. oocysts were detected only in parrots (16.67%). Helminth eggs and Giardia sp. cysts were not found in aviary birds. However no parasites were detected in nightingales.

Atoxoplasma spp. Infection in Captive Canaries (Serinus canaria)

Clinical signs, histopathological and ultrastructural findings associated with Atoxoplasma spp. natural infection in captive canaries (Serinus canaria) are described. Intracytoplasmic Atoxoplasma-like protozoa were found in the liver and lung. In the liver, protozoa were found in hepatocytes and Kupffer's cells and were associated with granulomatous hepatitis and a marked bile duct hyperplasia. An usual finding was the presence of infected mononuclear cells adhered to the endothelium of the blood vessels in lung. The diagnosis was confirmed by ultrastructural examination of reprocessed paraffin-embedded tissues.

Parasites affect song complexity and neural development in a songbird

There is now considerable evidence that female choice drives the evolution of song complexity in many songbird species. However, the underlying basis for such choice remains controversial. The developmental stress hypothesis suggests that early developmental conditions can mediate adult song complexity by perturbing investment in the underlying brain nuclei during their initial growth. Here, we show that adult male canaries (Serinus canaria), infected with malaria (Plasmodium relictum) as juveniles, develop simpler songs as adults compared to uninfected individuals, and exhibit reduced development of the high vocal centre (HVC) song nucleus in the brain. Our results show how developmental stress not only affects the expression of a sexually selected male trait, but also the structure of the underlying song control pathway in the brain, providing a direct link between brain and behaviour. This novel experimental evidence tests both proximate and ultimate reasons for the evolution of complex songs and supports the Hamilton-Zuk hypothesis of parasite-mediated sexual selection. Together, these results propose how developmental costs may help to explain the evolution of honest advertising in the complex songs of birds.

Plasmodium (Haemamoeba) cathemerium gene sequences for phylogenetic analysis of malaria parasites

The DNA sequence information on avian malaria parasites of the genus Plasmodium is quite limited. At present, sequences of only 6 out of 34 valid species are available. However, sequence data of avian malaria parasites are particularly important with regard to the resolution of the phylogenetic relationships of the most virulent human malaria agent, Plasmodium falciparum. The question as to whether P. falciparum originates from avian or from mammalian parasites would contribute to our understanding of its biology and would probably facilitate the interpretation of experimental results. To add to the body of molecular data, we sequenced three genes (cytochrome b, 18 SSU rRNA, caseinolytic protease C) of different organellar origin of one of the most widespread avian malaria parasites, Plasmodium (Haemamoeba) cathemerium, which once used to be an important laboratory in vivo model in human malaria research. The analysis of the new P. cathemerium sequences in direct comparison with the rodent parasite P. berghei and the four human malaria parasites by pairwise distance calculation do not suggest a closer relationship of P. cathemerium to P. falciparum than to the other species involved.

[Natural helminth infection in Sicalis flaveola (Linnaeus, 1766), by Acuaria mayori Lent, Freitas and Proença, 1945 (Nematoda: Acuarioidea) in Brazil]

This is the first report of a natural infection in the saffron finch Sicalis flaveola (Linnaeus, 1766) captured in Brazil, with the establishment of a new host record for the acuarioid nematode Acuaria mayori Lent, Freitas and Proença, 1945, previously referred in Cyanocorax chrysops (Vieillot, 1818) from Paraguay and Sporophila caerulescens caerulescens (Vieillot, 1823) and C. cyanomelas (Wied, 1821) from Brazil and Myarchus nuttingi (Ridgway, 1883) from Costa Rica.

Measuring the effects of an ever-changing environment on malaria control

The effectiveness of malaria control measures depends not only on the potency of the control measures themselves but also upon the influence of variables associated with the environment. Environmental variables have the capacity either to enhance or to impair the desired outcome. An optimal outcome in the field, which is ultimately the real goal of vaccine research, will result from prior knowledge of both the potency of the control measures and the role of environmental variables. Here we describe both the potential effectiveness of control measures and the problems associated with testing in an area of endemicity. We placed canaries with different immunologic backgrounds (e.g., naïve to malaria infection, vaccinated naïve, and immune) directly into an area where avian malaria, Plasmodium relictum, is endemic. In our study setting, canaries that are naïve to malaria infection routinely suffer approximately 50% mortality during their first period of exposure to the disease. In comparison, birds vaccinated and boosted with a DNA vaccine plasmid encoding the circumsporozoite protein of P. relictum exhibited a moderate degree of protection against natural infection (P < 0.01). In the second year we followed the fate of all surviving birds with no further manipulation. The vaccinated birds from the first year were no longer statistically distinguishable for protection against malaria from cages of naïve birds. During this period, 36% of vaccinated birds died of malaria. We postulate that the vaccine-induced protective immune responses prevented the acquisition of natural immunity similar to that concurrently acquired by birds in a neighboring cage. These results indicate that dominant environmental parameters associated with malaria deaths can be addressed before their application to a less malleable human system.

Trypanosoma avium: experimental transmission from black flies to canaries

Trypanosomes identified as Trypanosoma avium were found in the ornithophilic black flies ( Eusimulium latipes) attacking buzzard nestlings ( Buteo buteo). Parasites formed plugs and rosettes in the hindgut of the vector and were attached on the cuticular lining of the black fly anterior intestine (ileum) by hemidesmosome-like plaques. Hindgut stages from infected black flies were experimentally transmitted into canaries ( Serinus canaria) by ingestion of vectors and by contamination of host conjunctiva. This is the first clear evidence of such transmission in avian trypanosomes. Parasites survived in peripheral blood of birds at the least 10 months. In contrast to the direct inoculation of insect stages, parasites from culture failed to produce infection in experimental birds; this has consequences for laboratory studies of host susceptibility and transmission.

Diagnosis of atoxoplasmosis in a canary (Serinus canarius) by histopathologic and ultrastructural examination

Our paper describes pathologic and ultrastructural features of a canary (Serinus canarius) infected by Atoxoplasma sp. Histologically, numerous mononuclear cells were observed in intestinal mucosa, liver, and spleen. Most of these cells contained a variable number of protozoal-like organisms. These organisms were identified as Atoxoplasma sp. by ultrastructural examination of reprocessed paraffin-embedded tissues.

Skeletal muscle ultrastructural pathology in Serinus canarius infected with Plasmodium cathemerium

Serinus canarius infected with Plasmodium cathemerium was used as an animal model in order to study the skeletal muscle compromise in malaria. Pectoral muscle biopsies were obtained from 7 infected female birds. The transmission electron microscopic study showed alterations of contractile and sarcotubular systems, mitochondrial abnormalities, lysosomal proliferation and nuclear pyknosis. The sarcolemma looked disrupted and separated from the necrotic fibres. Capillary abnormalities included endothelial degeneration with proliferation of lysosomal structures, penetration of endothelial cell by the parasites and necrosis. A mononuclear cell infiltrate formed by plasmocytes, lymphocytes and macrophages was observed. This investigation shows that skeletal muscle is an important target tissue for some malaria parasites.

The Leucocytozoidae of South African birds: Passeriformes

The leucocytozoids of ten families of Passeriformes--Estrildidae, Fringillidae, Laniidae, Nectariniidae, Passeridae, Ploceidae, Promeropidae, Pycnonotidae, Sturnidae and Zosteropidae--are reviewed. Leucocytozoon roubaudi from the Estrildidae, L. fringillinarum from the Fringillidae, L. balmorali from the Laniidae, L. gentili from the Passeridae, L. bouffardi from the Ploceidae, L. brimonti from the Pycnonotidae and L. zosteropis from the Zosteropidae are re-described. Leucocytozoon dutoiti, L. nectariniae, L. deswardti, L. pycnonoti and L. sturni are new species described from the Fringillidae (Carduelinae), Nectariniidae, Promeropidae, Pycnonotidae and Sturnidae respectively while L. monardi is considered to be a synonym of L. gentili and L. molpastis is considered to be a synonym of L. brimonti.

Pathology of experimental Sarcocystis falcatula infections of canaries (Serinus canarius) and pigeons (Columba livia)

Sarcocystis falcatula is an apicomplexan parasite with a broad range of avian intermediate hosts. The pathology and pathogenesis of infection with this parasite has been studied experimentally in the budgerigar (Melopsittacus undulatus). The present study quantitatively examines the pathology of this parasite in canaries (Serinus canarius) and pigeons (Columba livia) and compares it with that found in budgerigars. The general progression of merogony and cyst formation is similar qualitatively to that seen in budgerigars, but it differs quantitatively. The principal site of precystic merogony is in pulmonary endothelial cells. The magnitude of pulmonary meront burdens (at similar inoculated dosages) varies in different intermediate host species. Merogony is less persistent than in budgerigars. Among the various species of birds, the magnitude of precystic merogony correlates differently with the magnitude of skeletal muscle cyst burdens. The distribution of cyst burdens among various muscles also differs. The composition of inflammatory cells differs among various avian species' response to S. falcatula. Pathologic changes quantitatively parallel tissue meront burdens (except possibly in the liver of canaries), resulting in an interstitial pneumonitis, hepatitis, and mild inflammatory lesions of other organs.

Description of Sarcocystis falcatula stiles, 1893, a parasite of birds and opossums

Sarcocystis falcatula Stiles, 1893 is re-described. Intermediate hosts of the parasite which was earlier described as Sarcocystis debonei Vogelsang, 1929 are species of passeriform, psittaciform, and columbiform birds. In these birds, muscle zoites are 6.88 X 2.19 (4.8-8.4 X 1.2-3.6) micron and are enclosed in a cyst wall with regular protrusions, 1-5 micron long. The convoluted primary wall has multiple thin areas in the osmiophilic layer. Microtubules originate in the ground substance and extend to the tips of the protrusions. The only known definitive host is the opossum, Didelphis virginiana; rats, cats, a dog, and a ferret could not be infected from muscle cysts. Sporocysts from opossums infected from five different infected avian sources measure 11.2 X 7.4 (9.6-12.0 X 6.0-8.4) micron.

Hemorrhagic disease in canaries (Serinus canarius)

Two aviaries were diagnosed as harboring an infectious and fatal disease of canaries (Serinus canarius) characterized by acute hepatocellular necrosis and associated with megaloschizonts of a protozoan parasite and extravasation of blood into the thoracoabdominal cavity.

Cryptosporidiosis in domestic birds

From March to June 1982, three cases of avian cryptosporidiosis were encountered in chickens, ducklings, and canaries. The bursa of Fabricius of chickens and ducklings were the main target organs and the agents were found to attach the microvillus border of the plical epithelium. In canaries, the parasites adhered to the microvillus border of mucosal epithelium of the proventriculus. Diagnoses were based on the microscopic pathology, the morphology of the parasites, and the type of attachment to epithelium. This represents the first authenticated evidence of cryptosporidial infection in Taiwan.

Life cycles of two isopora species in the canary, Serinus canarius Linnaeus

The endogenous stages of Isospora serini Arogão and Isospora canaria Box are described from experimentally infected canaries, Serinus canarius Linnaeus. Unlike other Coccidia, the first part of the I. serini life cycle takes place in mononuclear phagocytes. Five asexual generations are described from this cell type; 2 additional asexual generations and the sexual stages take place in the intestinal epithelium. Isospora canaria, on the other hand, has a conventional coccidian life cycle in that all of the endogenous stages are in the epithelium of the small intestine, with 3 asexual generations and the sexual generation described in the duodenal epithelium. The 2 species differ in their position relative to the nucleus of the intestinal epithelial cell. Isospora serini is usually on the lumenal side of the nucleus while I. canaria is below the nucleus, toward the basement membrane. The prepatent period is 4-5 days for I. canaria and 9-10 days for I. serini. Patency lasts for 11-13 days in I. canaria infections, but duration of oocyst output is more chronic in I. serini infections, persisting for as long as 231 days. Both species have a diurnal periodicity of oocyst discharge which occurs in late afternoon and evening.

Plasmodium (Giovannolaia) pedioecetii from gallinaceous birds of Colorado

Forty-nine Colorado birds of 6 galliform species were positive for Plasmodium (Giovannolaia) pedioecetii which we feel to be the same parasite described by Wetmore (1939) from a shaptailed grouse from North Dakota. Except for its presence in Darwin's tinamou (Nothura darwinii) from Colorado, it has been reported only from gallinaceous birds. Most stages were predominantly subpolar to polar. There were a daily 8 am to noon peak of merozoite production, but no synchronicity. Merozoite number ranged from 8 to 22, with a mean of 10.9. Gametocytes were long and slender, some curving around one end of the host nucleus.

Fine structure of the oocyst walls of Isospora serini and Isospora canaria and excystation of Isospora serini from the canary, Serinus canarius L

Oocysts of Isospora serini and Isospora canaria, from the canary Serinus canarius, were broken, added to a cell suspension, fixed in Karnovsky's fluid, and studied in the electron microscope. The oocyst wall of each species had an electron-lucent inner layer, a more osmiophilic middle layer and an outer layer of electron-lucent (I. serini) or electron-dense material interspersed with some electron-lucent material (I. canaria). A few, relatively large lipid-like bodies were present in the outer or middle layer of the oocyst wall of I. canaria. As many as 9 membranes were present in the oocyst wall of I. canaria and 3 in that of I. serini. When exposed to a trypsin-sodium taurocholate fluid, sporozoites of I. serini excysted from 5-month-old sporocysts in vitro, but not from sporocysts stored for more than 6 months. No excystation occurred in 15-month-old I. canaria sporocysts. Similarities and differences in excystation between I. serini and other Isospora, Eimeria, and Sarcocystis species are discussed.