Studies of Growth and Development of Gametocytes in Haemoproteus columbae Kruse*

SYNOPSIS As determined by their ability to exflagellate and round up, it took the macrogametocyte and the microgametocyte of Haemoproteus columbae in pigeons 68 and 116 h, respectively, after patency to reach maturity. Pigment granules appeared in the undifferentiated gametocytes 8 h after invasion of blood. Vacuoles were observed in young gametocytes and persisted in the older forms. The growth curve of H. columbae is close to the sigmoidal curve for growth in protozoa. Multiple infection was noticed in pigeons with high levels of parasitemia, but no more than 2 gametocytes reached maturity; such multiple infections were rare in relapses. The sex ratio of the gametocytes was 1:1. Strong lateral displacement of the nuclei of infected erythrocytes was the rule; hypertrophy was negligible.     

A New Vector of Haemoproteus colmubae in England

SUMMARY. Haemoproteus columbae of English wood pigeons ( Columba palumbus palumbus L.) was found to undergo sporogony in Ornithomyia avicularia. It is suggested that this insect is a vector of H. columbae , in spite of the failure of six attempts to transmit the haemosporidian to uninfected domestic pigeons ( C. livia var. domestica ) by the bite, or injection, of infected O. avicularia.     

Haemoproteus palumbis sp. nov. (Sporozoa, Haemosporina) of the English Wood-Pigeon Columba p. palumbus

SYNOPSIS. Haemoproteus palumbis sp. nov. is described from the English wood-pigeon, Columba p. palumbus. Its pigmented gametocytes inhabit erythrocytes and resemble those of H. columbae (in C. livia ) but may be slightly longer and narrower. It is characterized by having oval or slightly lobed, not elongate, schizonts in endothelial cells of lung and heart, a prepatent period of 14 days, and a sporogonic cycle in the hippoboscid fly Ornithomya avicularia lasting 6 1/2–7 days. H. palumbis sp. nov. cannot infect C. livia but can infect a small proportion of individuals of Pseudolynchia canariensis , the vector of H. columbae.     

Characteristics of the haemoproteid community in an expanding white-winged dove population

The haemoproteid community of 171 eastern white-winged doves (Zenaida asiatica asiatica) from the expanding Texas population was examined using thin blood smears. During summer 1997, heart blood was taken from doves within their historical breeding range (Lower Rio Grande Valley of Texas), an intermediate region (San Antonio and surrounding area), and the new breeding periphery (north central to southeast Texas). Two species were found: Haemoproteus columbae and Haemoproteus sacharovi. Infracommunities rarely occurred in heart blood, as only 20 of 132 infected doves demonstrated gametocytes of both species. Overall prevalence of H. columbae and H. sacharovi was 77 and 15%, respectively. Prevalence of H. columbae was higher in the Lower Rio Grande Valley (LRGV) and intermediate regions than at the periphery, higher in adults than juveniles, and similar between males and females. Prevalence of H. sacharovi was lower in the LRGV than intermediate and peripheral regions, similar between juveniles and adults, and higher in females than males. Mean density of H. columbae and H. sacharovi was 15.9 +/- 2.7 and 0.3 +/- 0.1 (mean +/- SE per 3,000 erythrocytes), respectively. Overall mean abundance of H. columbae and H. sacharovi was 12.2 +/- 2.2 and 0.04 +/- 0.02, respectively. Mean abundance of H. columbae was higher in the LRGV and intermediate regions than at the periphery and was similar between host age and between host sex; H. sacharovi was similar among regions, host age, and host sex. This study emphasizes the importance of using prevalence, density, and abundance data to assess haemoproteid community structure and pattern.     

Geographical variation in blood parasites in feral pigeons: the role of vectors

Prevalence and intensity of blood parasites are known to vary in space within a same species, yet the causes underlying such variation are poorly known. Theoretically, blood parasites variation can be attributed to differences to exposure to parasite vectors and/or to differences in host susceptibility. Here, we show that prevalence of Haemoproteus columbae in feral pigeons Columba livia varied among five near-by populations (range 15%-100%), paralleled by variation in the abundance of its main vector, the louse flies Pseudolynchia canariensis. Geographic variation in intensity of blood parasites did not covary with abundance of vectors. Within populations, older individuals had a higher probability of being parasitized than younger ones, whereas younger birds, when infected, suffered higher intensities. Furthermore, we found no evidence of sex-related differences neither in prevalence nor in intensity of blood parasite infections. To demonstrate that geographical variation in prevalence was actually due to differences in vector exposure, we conducted two experiments based on translocation of unparasitized pigeons from a vector-free area to an area where both the parasite and vector were abundant. With the first experiment, we demonstrated that unparasitized pigeons were not resistant to the parasite because when transmission was possible pigeons became parasitized in a few months. With the second experiment, in which half of the pigeons were prevented from contacts with the vector, we ruled out the posibility that pigeons we considered as unparasitized would have suffered from latent infections. Therefore, both observational and experimental evidence supports the view that vector abundance is the major factor influencing the spatial variation in prevalence of H. columbae in pigeons.     

Ultrastructural Study of Gametocytes and Gametogenesis of Haemoproteus metchnikovi

SYNOPSIS. The ultrastructure of gametocytes and microgametogenesis of Haemoproteus metchnikovi , an intracellular malaria parasite of chelonians, was compared with other malarial parasites. Gametocytes resemble those described for other avian, reptilian and mammalian malarial parasites. The process of microgametogenesis is similar in many respects to that reported for Leucocytozoon simondi (Aikawa et al., 1970) and Haemoproteus columbae (Bradbury and Trager, 1968). Atypical centrioles are described from both microgametocytes and macrogametocytes. Axoneme development begins before the microgametocyte leaves the host red blood cell. Fully developed microgametes which bud off from the parent gametocyte contain a single axoneme with the typical 9 + 2 pattern of microtubules.     

Differentiation of Gametocytes in Microcultures of Human Blood Infected with Plasmodium falciparum*

SYNOPSIS. Gametocytes differentiated from ring-stage parasites in microcultures of human blood infected with Plasmodium falciparum. Immature gametocytes could be distinguished morphologically from late asexual trophozoites after ～ 40 h of culture. Differentiation into crescentic forms took several days and the incorporation of [³H]-isoleucine by developing gametocytes was demonstrated. About 1% of red cells contained gametocytes at the maximum densities attained. Differentiation of gametocytes occurred either directly from rings placed in culture or from the progeny of subsequent cycles of schizogony and invasion in vitro. The latter occurrence was confirmed by the development of gametocytes in marker fetal red cells added to cultures, although fetal red cells provide a less favorable environment than those with HbA for growth of the parasites.     

The Host-Restriction of Haemoproteus sp. indet. of the Wood-Pigeon Columba p. palumbus

SYNOPSIS. Earlier experiments suggested that the species of Haemoproteus which infects English wood-pigeons ( Columba p. palumbus ) and is transmitted by the hippoboscid dipteran fly Ornithomya avicularia , was unable to infect Columba livia domestica , a host of H. columbae . This has now been confirmed by the injection of sporozoites into two pairs of pigeons, one of each species; in both experiments the C. palubus developed parasitemia while the C. livia did not. It has also been shown that this species of Haemoproteus can complete sporogony in a small proportion (2/73) of Pseudolynchla canariensis , the vector of H. columbae .     

The prevalence and intensity of external parasites in domestic pigeons (Columba livia domestica) in Egypt with special reference to the role of deltamethrin as insecticidal agent

This study aimed to investigate the prevalence and intensity of external parasites in domestic pigeons in Giza, Egypt, from January 2020 to December 2020. A total of 300 domestic pigeons (25 pigeons per month) were examined. The birds were divided into groups based on their age. The oxidative stress parameters; serum zinc concentration, serum malondialdehyde (MDA), and serum Nitric oxide were evaluated in single and mixed external parasitic infestations. The prevalence of external parasites in examined pigeons was 80.3%. The detected parasites were Pseudolynchia canariensis (P. canariensis), Hippobosca equina (H. equina), Columbicola columbae (C. columbae), Menopon gallinae (M. gallinae), Knemidocoptes species (spp.) and Dermanyssus gallinae (D. gallinae); their incidences were 41.6, 26, 7, 5,0.33 and 0.33%, respectively. The highest infestation was recorded in both spring and summer. . The incidence of disease was higher in squabs and young birds than in adults. The mixed external parasitic infestation was recorded in this study. The infected birds showed decreased serum zinc concentration and elevated MDA and serum Nitric oxide levels. In conclusion, regular monthly treatment with deltamethrin is recommended as an effective drug in the treatment of the infested birds and succeeded in reducing the incidence of externalparasites in the treated birds; in addition, pigeon management measures must be implemented to reduce the risk of external parasites.     

Experimental life cycle of Ascaridia columbae in intravenously infected pigeons, Columba livia.

The fate and routes of migration of infective larvae of Ascaridia columbae were studied in intravenously (i.v.) infected pigeons. Larvae were able to complete a trachael migration, and arrived at the small intestine where they established a patent infection. Granulomas were observed and histopathologically described in the lungs of i.v. infected birds.     

A SURVEY OF BLOOD PARASITES OF BIRDS IN THE MASCARENE ISLANDS, INDIAN OCEAN: WITH DESCRIPTIONS OF TWO NEW SPECIES AND TAXONOMIC DISCUSSION

A survey was carried out on the prevalence of blood parasites in birds in the Mascarene Islands. Smears from 357 birds of 25 species in 12 families were examined, of which 150 (42%) were found to harbour blood parasites. The most common parasites were Leucocytozoon ; a new species, L. zosteropis , is described from the Grey White-eye Zosterops borbonica mauritiana. This parasite was observed in smears from 68 birds of three species: Z. borbonica, Z. chloronothos and Z. olivacea. Other species of Leucocytozoon identified were L. fringillinarum from fodies, sparrows and a bulbul and L. marchouxi from two doves.
Haemoproteus was found only in domestic pigeons Columba livia and identified as H. columbae. Plasmodium relictum, P. vaughani and an unidentified species with elongate gametocytes were found in Zosterops , and Plasmodium sp. of low infection observed in other hosts. Trypanosoma mayae is redescribed from the House Sparrow Passer domesticus and the Mauritius Fody Foudia rubra , and considered to be a valid species. A new species of trypanosome, Trypanosoma phedinae , is described from the Malagasy Swallow Phedina b. borbonica. Other birds were found to harbour low infections of unidentified species of trypanosomes. A small number of birds were infected with Atoxoplasma , haemogregarines and Rickettsia-like organisms. An unidentified organism with a predilection for eosinophils was observed in several Mascarene Swiftlets Collocalia francica.
The results are discussed in relation to the possible effects of the parasites on the birds of the Mascarene Islands and comparisons made with the results of similar surveys on other Indian Ocean Islands.     

Haemoproteus columbae: course of infection, relapse and immunity to reinfection in the pigeon.

Studies were performed on the course of infection, relapse, and immunity to reinfection in 11 young pigeons infected with the avian malaria parasite Haemoproteus columbae Kruse. The prepatent period in our experiments varied between 22 and 37 days. The intensity and length of the initial infection period showed wide variations. During this period an initial periodicity of gametocyte production of about 12 days with peaks at about 6-8 and 18-20 days after patency was observed. The various modes of infection (fly bite, intramuscular, intravenous, or intraperitoneal inoculation of sporozoites) did not influence the intensity of the initial infection. No pathogenicity due to heavy infection with the parasite was observed. There was no periodicity of relapse occurrence, nor any correlation between the frequency of relapse and the intensity of the initial infection, and the phenomenon was not influenced by seasonal changes. Pigeons (Columba livia) that had recovered from previous infections were susceptible to reinfection, whereas pigeons with chronic infection acquired immunity (premunition).     

Parasites of Columba livia (Aves: Columbiformes) in Tenerife (Canary Islands) and their role in the conservation biology of the laurel pigeons

The prevalence and intensity of the parasites from 50 wild doves (Columba livia) from the city of Santa Cruz de Tenerife, in the island of Tenerife (Canary Archipelago), were studied. The following ectoparasites were found in apparently healthy pigeons (prevalences are shown in percentage (%) and mean intensities with their standard deviations): the acari Dermanyssus gallinae (De Geer, 1778) (6, 241.0 +/- 138.9) and Tinaminyssus melloi Fain, 1962 (10%, 218.3 +/- 117.3); the louses, Columbicola columbae Linnaeus, 1758 (100%, 111.4 +/- 76.8) and Campanulotes bidentatus Scopoli, 1763 (94%, 48.4 +/- 26.6); and the pigeon fly, Pseudolynchia canariensis Macquart, 1839 (36%, 6.2 +/- 1.6). The endoparasites we found were: a haemoprotozoan species, Haemoproteus columbae Kruze, 1890 (82%, 14.8 +/- 10.3 per 1000); coccidian oocysts, Eimeria sp. (50%, 0.2 x 10(3) +/- 1.7 x 10(3) per gr); a cestode species Raillietina micracantha (Fuhrmann, 1909) López Neyra, 1947 (44%, 12.3 +/- 9.4); and four nematode species, Tetrameres (Tetrameres) fissispina (Diesing, 1861) Travassos, 1915 (4%, 99.5 +/- 34.1), Synhimantus (Dispharynx) spiralis (Molin, 1858) (8%, 46.8 +/- 11.6), Ascaridia columbae (Gmelin, 1790) Travassos, 1913 (40%, 8.4 +/- 8.8) and Aonchotheca sp. (18%, 6.0 +/- 3.1). Several species detected in our study can be pathogens for C. bollii and C. junoniae, which are endemic pigeons of the Canary Islands, considered endangered species. Parasites (ectoparasites, protozoa and helminths) of C. livia found in Tenerife and others from wild and farm birds in the island were considered as healthy controls.     

Activity of clinically relevant antimalarial drugs on Plasmodium falciparum mature gametocytes in an ATP bioluminescence "transmission blocking" assay

Background

Current anti-malarial drugs have been selected on the basis of their activity against the symptom-causing asexual blood stage of the parasite. Which of these drugs also target gametocytes, in the sexual stage responsible for disease transmission, remains unknown. Blocking transmission is one of the main strategies in the eradication agenda and requires the identification of new molecules that are active against gametocytes. However, to date, the main limitation for measuring the effect of molecules against mature gametocytes on a large scale is the lack of a standardized and reliable method. Here we provide an efficient method to produce and purify mature gametocytes in vitro. Based on this new procedure, we developed a robust, affordable, and sensitive ATP bioluminescence-based assay. We then assessed the activity of 17 gold-standard anti-malarial drugs on Plasmodium late stage gametocytes.

Methods and Findings

Difficulties in producing large amounts of gametocytes have limited progress in the development of malaria transmission blocking assays. We improved the method established by Ifediba and Vanderberg to obtain viable, mature gametocytes en masse, whatever the strain used. We designed an assay to determine the activity of antimalarial drugs based on the intracellular ATP content of purified stage IV–V gametocytes after 48 h of drug exposure in 96/384-well microplates. Measurements of drug activity on asexual stages and cytotoxicity on HepG2 cells were also obtained to estimate the specificity of the active drugs.

Conclusions

The work described here represents another significant step towards determination of the activity of new molecules on mature gametocytes of any strain with an automated assay suitable for medium/high-throughput screening. Considering that the biology of the forms involved in the sexual and asexual stages is very different, a screen of our 2 million-compound library may allow us to discover novel anti-malarial drugs to target gametocyte-specific metabolic pathways.     

Parasite mediated mortality and host immune response explain age-related differences in blood parasitism in birds

An important pattern in host-parasite assemblages is a higher intensity of parasites in juveniles than in adults, but the reasons for these differences remain obscure. Three non-mutually exclusive hypotheses have been proposed: (1) heavily parasitized juveniles die before being recruited into the adult population ('selection' hypothesis); (2) the development of an acquired immunity by the host in front of the parasite reduces the intensity of the parasite in adult hosts ('immunity' hypothesis); and (3) differences in behavior makes adults less exposed to the parasite than juveniles ('vector exposure' hypothesis). Having rejected the 'vector exposure' hypothesis in a previous study, here we tested the 'selection' and 'immunity' hypotheses in feral pigeons (Columba livia) infected by the blood parasite Haemoproteus columbae. In agreement with the 'selection' hypothesis, young (but not adult) pigeons that were highly parasitized had a lower probability of surviving until adulthood, independent of their body condition. However, selection was not strong enough to account for the observed differences in parasite intensity between age-classes, and after selection parasite intensity of survivors still remained 85% higher in juveniles than in adults. In contrast, the 'immunity' hypothesis offered a greater explanatory power. The intensity of blood parasites in young pigeons, but not in adults, decreased over time so dramatically that by the time they had become adults their intensities were indistinguishable from that typically seen in adults. Therefore, while selection against highly parasitized juveniles can contribute to some extent to a reduction in parasitism seen in the adult population, age-specific blood parasitism in feral pigeons is best explained as a transitory phase just before the host develops an effective immune response.     

Life history of a malaria parasite (Plasmodium mexicanum): independent traits and basis for variation

Plasmodium mexicanum, a malaria parasite of lizards, exhibits substantial variation among infections in the life-history traits which define its blood-dwelling stages. Such variation in life histories among infections is common in Plasmodium and may influence the ecology and evolution of the parasite's transmission success and virulence. Insight into these issues requires identification of independent traits (some traits may be bound by developmental trade-offs) and the importance of genetic versus host effects producing the variation. We studied 11 life-history traits in 120 induced infections of P. mexicanum in its natural lizard host (20 each from six donor infections). The traits varied among infections and fell into three clusters: rate/peak (rate of increase and peak parasitaemia of asexuals and gametocytes), time (duration of pre-patent period and the infection's growth) and maturity (timing of first gametocytes). Thus, few life-history traits define an infection in the lizard's blood. Donor effects were significant for ten traits and two trait clusters (maturity was the exception) suggesting genetic differences among infections may influence the rate of increase and peak parasitaemia, but not the timing of the first production of gametocytes.     

The dynamics of naturally acquired immune responses to Plasmodium falciparum sexual stage antigens Pfs230 & Pfs48/45 in a low endemic area in Tanzania

Background

Naturally acquired immune responses against sexual stages of P. falciparum can reduce the transmission of malaria from humans to mosquitoes. These antigens are candidate transmission-blocking vaccines but little is known about the acquisition of sexual stage immunity after exposure to gametocytes, or their longevity and functionality. We conducted a longitudinal study on functional sexual stage immune responses.

Methodology/Principal Findings

Parasitaemic individuals (n = 116) were recruited at a health centre in Lower Moshi, Tanzania. Patients presented with gametocytes (n = 16), developed circulating gametocytes by day 7 (n = 69) or between day 7 and 14 (n = 10) after treatment or did not develop gametocytes (n = 21). Serum samples were collected on the first day of gametocytaemia and 28 and 84 days post-enrolment (or d7, 28, 84 after enrolment from gametocyte-negative individuals). Antibody responses to sexual stage antigens Pfs230 and Pfs48/45 were detected in 20.7% (72/348) and 15.2% (53/348) of the samples, respectively, and were less prevalent than antibodies against asexual stage antigens MSP-1₁₉ (48.1%; 137/285) and AMA-1 (52.4%; 129/246)(p<0.001). The prevalence of anti-Pfs230 (p = 0.026) and anti-Pfs48/45 antibodies (p = 0.017) increased with longer duration of gametocyte exposure and had an estimated half-life of approximately 3 months. Membrane feeding experiments demonstrated a strong association between the prevalence and concentration of Pfs230 and Pfs48/45 antibodies and transmission reducing activity (TRA, p<0.01).

Conclusions/Significance

In a longitudinal study, anti-Pfs230 and Pf48/45 antibodies developed rapidly after exposure to gametocytes and were strongly associated with transmission-reducing activity. Our data indicate that the extent of antigen exposure is important in eliciting functional transmission-reducing immune responses.