Hemoparasites are microscopic parasites that live in the blood of their hosts, and reptiles are no exception to these intriguing organisms. Understanding hemoparasites of reptiles, especially the various Plasmodium species, is crucial for veterinary science, ecology, and herpetology students. This article provides a comprehensive overview of several key Plasmodium parasites found in African reptiles, detailing their life stages, host interactions, and geographical distribution.
What are Hemoparasites of Reptiles?
Hemoparasites of reptiles are diverse, but a significant group includes species from the genus Plasmodium, commonly known for causing malaria in other vertebrates. These parasites primarily infect red blood cells, impacting the host's health in various ways. Their life cycles often involve both a vertebrate host (the reptile) and an invertebrate vector, though the vectors for many reptilian Plasmodium species are still unknown or poorly understood. This guide will explore specific Plasmodium species, focusing on their unique characteristics and ecological contexts.
Exploring Key Plasmodium Species in Reptiles
We'll delve into several notable Plasmodium species, primarily found in African lizards and chameleons, based on detailed scientific observations.
Plasmodium tanzaniae: A Chamaeleon Parasite
Discovered in Chamaeleo werneri from Tanzania, P. tanzaniae is characterized by its meronts, which are typically fan-shaped or oblong. These meronts measure 6–12 × 4–7 μm and produce 8–22 merozoites. They are predominantly found in proerythrocytes (immature red blood cells), with pigment dispersed as large, dark golden granules or clumped at the base of fans. The gametocytes are usually elongate, 8–19 × 4–9 μm, and are almost entirely erythrocytic (in mature red blood cells). Macrogametocytes are larger and slightly more elongate than microgametocytes. Interestingly, some gametocytes exhibit a clear, light bluish-green area, possibly where pigment previously aggregated.
Effects on the host include hypertrophy (enlargement) of both host cells and their nuclei when meronts are present, though distortion is rare. Gametocytes cause host cells to distort but not hypertrophy, often displacing nuclei.
Plasmodium arachniformis: The Arachnoid Anomaly
Also found in Chamaeleo werneri in Tanzania, P. arachniformis is notable for its young asexual stages that can assume bizarre, polymorphic forms. Meronts often form fans before segmentation, with merozoites sometimes linearly arranged, connected by thin cytoplasmic bridges, giving them an “arachnoid” appearance. Mature meronts are 4–12 × 2–7 μm and produce 4–12 merozoites. They occur in both mature and immature erythrocytes. Gametocytes are typically elongate and slender, 6–17 × 3–8 μm. While macrogametocytes are longer and more slender, both sexes are similar in size. Small dark golden pigment granules are dispersed in both sexes.
P. arachniformis generally does not cause hypertrophy of host erythrocytes, and distortion is seldom observed. Meronts can enlarge host cell nuclei, but distortion or displacement is rare. Gametocytes may cause hypertrophy of nuclei in some infections.
Plasmodium holaspi: Marginal Position and Chromatin Blocks
Identified in Holaspis guentheri from Tanzania, P. holaspi is distinguished by its young asexual stages occupying marginal positions in erythrocytes. Meronts are usually oblong or rosette-shaped, 5–13 × 4–7 μm, containing 8–18 merozoites. A single, dark, irregular pigment mass is characteristic. Elongate gametocytes are 6–18 × 3–8 μm, with conspicuous, dispersed, irregular dark pigment granules. A unique feature is the presence of large masses of intensely reddish-staining chromatin in maturing gametocytes of both sexes. Exoerythrocytic (EE) meronts are commonly found in the lungs of infected hosts, appearing ovoid to elongate and containing numerous nuclei.
This parasite can cause hypertrophy and distortion of host erythrocytes and displacement of their nuclei. Gametocytes commonly distort host cells and displace nuclei, but rarely distort the nuclei themselves.
Plasmodium uluguruense: Fan-shaped Meronts in Geckos
Found in Hemidactylus platycephalus from Tanzania, P. uluguruense has asexual stages parasitic in both mature and immature erythrocytes. Meronts are typically fan-shaped, 4–10 × 2–6 μm, and produce 4–12 merozoites. Light golden pigment granules aggregate at the base of these fans. Ovoid gametocytes are 5–10 × 4–7 μm, with dark greenish-yellow to black pigment granules that tend to aggregate in a single focus near the gametocyte margin. Microgametocytes are longer and larger than macrogametocytes but do not differ in shape. This species shows a prevalence of up to 64.8% in certain localities.
Effects on the host vary with infection phase. In active infections, host cells with meronts can be hypertrophied and distorted, and their nuclei enlarged and displaced. In chronic infections, these effects are less pronounced.
Plasmodium fischeri: Small Asexual Stages
This species infects Chamaeleo f. fischeri in Tanzania. Its small asexual stages are rounded with a large central vacuole and no filiform cytoplasmic projections. Mature meronts are estimated around 9 × 6 μm, producing 21–25 merozoites arranged as a broad fan with large dark pigment granules concentrated near the base. Gametocytes are oblong to elongate, 8–11 × 5–8 μm. Pigment in microgametocytes consists of large, irregular dark granules, while macrogametocytes have smaller, dispersed granules.
Ball and Pringle (1965) observed little or no hypertrophy of cells infected with P. fischeri meronts, though nuclear displacement and cell distortion are present for both meronts and gametocytes.
Plasmodium gologoloense: Proerythrocyte Preference
Identified in Bradypodion oxyrhinum from Tanzania, P. gologoloense typically presents with oval or round meronts, 5–7 × 4–6 μm, yielding 6–14 merozoites. These meronts most commonly parasitize proerythrocytes. Pigment appears as one or two prominent, often squarish, light greenish-gold granules. Gametocytes are usually ovoid or round, 5–11 × 4–6 μm. Microgametocytes are generally larger and more elongate than macrogametocytes. Pigment is dispersed along gametocyte margins as prominent dark gold granules.
Erythrocytes infected by meronts, and their nuclei, are hypotrophic (reduced in size), but when occupied by gametocytes, they are normal in dimensions.
Plasmodium uzungwiense: Immature Erythrocyte Specialist
Also found in Chamaeleo werneri from Tanzania, P. uzungwiense is unique for primarily infecting immature erythrocytes across all stages. Meronts are 4–8 × 3–6 μm, typically fan-shaped, oblong, or rounded, producing 4–12 merozoites. Pigment consists of large dark golden granules clumped at the base of the fan or in a single focus. Most gametocytes are elongate, 5–13 × 3–7 μm. Macrogametocytes are slightly longer and more slender than microgametocytes. Pigment is dispersed as small dark golden granules, tending to be marginal in macrogametocytes and somewhat aggregated in microgametocytes.
Neither asexual nor sexual stages induce hypertrophy in host proerythrocytes. Meronts do not distort host cells or nuclei. Gametocytes may distort host cells and rarely their nuclei, but usually displace the latter, and do cause enlargement of the proerythrocyte nucleus.
Plasmodium cnemaspi: Gecko Parasite in Rainforests
Infecting Cnemaspis barbouri from Tanzania, P. cnemaspi has variably shaped meronts (6–13 × 3–7 μm) that parasitize both mature and immature red blood cells, containing 8–24 merozoites. Proerythrocytic meronts are larger and produce more merozoites. Dark, greenish-yellow pigment granules are loosely aggregated. Gametocytes parasitize only erythrocytes, typically elongate in active infection and ovoid/round in chronic infection, 7–14 × 3–9 μm. The dark pigment granules are dispersed in both sexes of gametocytes, which do not differ in dimensions. One EE meront was observed in a monocyte, and phanerozoites (EE stages) were found in the lungs and gut wall.
Host cells with meronts are not enlarged, but erythrocyte nuclei can be hypertrophied. Gametocytes often distort host cells and displace their nuclei. In chronic infections, gametocytes cause striking hypotrophy of host erythrocytes and their nuclei.
Plasmodium loveridgei: Polymorphic Meronts in Lygodactylus
This species, found in Lygodactylus l. luteopicturatus and Lygodactylus capensis grotei in Tanzania, features polymorphic, usually elongate or fan-shaped meronts (5–15 × 3–7 μm) that parasitize both mature and immature erythrocytes, producing 6–26 merozoites. Proerythrocytic meronts are larger and produce more merozoites. Dark greenish-gold pigment granules (1–3) are dispersed. Gametocytes are elongate, rarely rounded, 8–23 × 3–11 μm. There is no sexual dimorphism in gametocyte dimensions, and their size is not affected by infection phase. Pigment is dispersed as dark greenish-gold-to-black granules. Phanerozoites are found in the heart and liver connective tissue.
Erythrocytes hosting meronts are hypertrophied in acute infections. Gametocytes cause hypertrophy and distortion of erythrocytes and their nuclei, commonly displacing nuclei. In chronic infections, gametocytes cause hypotrophy and distortion.
Plasmodium maculilabre: A Congo Basin Species
Reported in Mabuya maculilabris from Congo, P. maculilabre has ovoid or round meronts (estimated ~10.0 × 6.9 μm) that may nearly fill the host erythrocyte, producing 15–20 merozoites. Gametocytes are ovoid to elongate, 7–13 × 5–8 μm. Macrogametocytes are longer, larger, and more elongate than microgametocytes. Pigment appears sparse in meronts but is dispersed as round dark granules in gametocytes.
Erythrocytes parasitized by either meronts or gametocytes are hypertrophied and often distorted, with nuclei displaced and sometimes distorted. This species is poorly described and requires further study.
Plasmodium agamae: Widespread Agama Parasite
Found in Agama agama across Africa (Sudan, Gambia, Ethiopia, Nigeria, Liberia, Sierra Leone, Congo, Kenya, Tanzania), P. agamae typically has fan-shaped meronts (4–11 × 3–6 μm) with 4–15 merozoites. Dimensions and merozoite numbers are similar in mature and immature erythrocytes. Gametocytes are 6–19 × 3–8 μm, with dimensions varying by sex and infection phase. Pigment forms as two or three coarse greenish-gold granules in meronts and is dispersed as fine-to-coarse, dark greenish-gold-to-black granules in both sexes of gametocytes. EE merogony occurs in hepatic and splenic macrophages and circulating monocytes. Sporogony has been observed in Culicoides nubeculosus, with oocysts developing in the midgut, though sporozoites did not reach salivary glands.
Infected lizards show an increase in immature erythrocytes and a slight reduction in hematocrit and hemoglobin. Maximal oxygen consumption decreases by about 20%. Host cells with gametocytes are hypotrophied in chronic infections, while meront infection can cause hypertrophy of host cell nuclei. The presence of encysted EE meronts in A. agama suggests a mechanism for long-term maintenance of chronic infections.
Plasmodium mossambica: Distinct Meronts in Agama mossambica
This species infects Agama mossambica in Tanzania. Meronts are elongate or oblong (5–15 × 3–7 μm), producing 6–34 merozoites, with more merozoites than P. agamae. Gametocytes are usually elongate, 6–17 × 3–8 μm, not sexually dimorphic in dimensions but differing in pigment distribution. Macrogametocytes often have a terminal aggregation of golden pigment clumps with small black granules, while microgametocytes have two or three large, black individual granules alongside small dispersed ones. Secondary EE meronts are common in circulating thrombocytes.
In active infections, meronts distort host erythrocytes and nuclei, displacing the latter. Gametocytes often distort host cells and displace nuclei. P. mossambica is distinguished from P. agamae by its larger, differently shaped meronts producing more merozoites, and distinct pigment distribution in gametocytes.
Plasmodium zonuriae: Curving Around Nuclei
Found in Cordylus vittifer and Pseudocordylus microlepidotus melanotus in South Africa, P. zonuriae has variably shaped meronts (7–17 × 4–9 μm) with peripherally arranged nuclei, producing 12–28 merozoites. Dark golden-brown pigment granules are dispersed within meronts, which tend to curve around the host cell nucleus. Gametocytes are usually elongate, 7–20 × 4–10 μm. Microgametocytes are more elongate than macrogametocytes. Dark brown pigment granules are dispersed in both sexes. Both meronts and gametocytes tend to curve around the host cell nucleus.
Heavy infections can lead to marked debilitation and severe anemia. Meronts cause hypertrophy of host cells and their nuclei, with distortion and displacement. Gametocytes also cause hypertrophy and distortion of erythrocytes and nuclei, and common displacement.
Plasmodium cordyli: Nucleophilic Meronts
Infecting Cordylus t. tropidosternum and Cordylus vittifer in Tanzania and South Africa, P. cordyli features polymorphic, usually fan-shaped meronts (4–7 × 3–6 μm) that produce 4–11 merozoites. Meronts are strongly nucleophilic, meaning they tend to associate with the host cell nucleus. Dark golden pigment granules are clumped at the base of fans or aggregated centrally. Gametocytes are round or ovoid, 5–8 × 4–7 μm, with no sexual dimorphism. Dark pigment granules are dispersed in macrogametocytes but form a single cluster in microgametocytes. Phanerozoic meronts are common in the endothelium and connective tissue of the heart, lungs, and kidney.
Meronts do not enlarge host cells or nuclei, but nuclei may be displaced. Gametocytes cause hypertrophy and distortion of erythrocytes and their nuclei, and commonly displace nuclei.
Plasmodium mabuiae: Nucleophilic Young Stages
This species is widespread in African Mabuya species (M. quinquetaeniata, M. striata, M. maculilabris). Meronts are usually fan-shaped (4–9 × 2–5 μm), producing 4–12 merozoites. Young asexual stages are strongly nucleophilic. Pigment is typically a dark yellow mass at the base of fan-shaped meronts. Gametocytes are predominantly elongate, 5–11 × 3–5 μm, with no sexual dimorphism in dimensions, though they are smaller and more rounded in chronic infections. Pigment often remains clumped in one or two foci. Microgametocytes often show a thick reddish-staining area.
Young asexual stages and immature gametocytes often appear to be touching host cell nuclei without apparent effect. Meronts rarely cause distortion but sometimes displace nuclei. Gametocytes uncommonly distort cells or nuclei, but more commonly displace nuclei. Host cells of gametocytes are slightly hypertrophied.
Plasmodium pitmani: Polymorphic Meronts in Mabuya
Infecting Mabuya striata, M. maculilabris, M. varia, and M. quinquetaeniata across East and Central Africa, P. pitmani has meronts most commonly fan-shaped, a rosette, or elongate (4–11 × 3–7 μm), producing 4–25 merozoites. Proerythrocytic meronts are larger and produce more merozoites. Pigment usually forms one or more pale yellow masses. Gametocytes are usually ovoid, 5–16 × 4–9 μm, without sexual dimorphism in size or shape. Pigment is dark greenish-gold, often loosely aggregated in one or two foci. EE meronts have been observed in heart muscle and spleen macrophages, as well as circulating monocytes.
In active infection, meronts sometimes distort host erythrocytes and their nuclei, and commonly displace nuclei. Gametocytes often distort host cells and usually displace their nuclei. In active infection, erythrocytes with meronts are hypotrophied, while gametocytes scarcely enlarge host cells.
Plasmodium diploglossi: Neotropical Elongate Meronts
Moving to Neotropical lizards, P. diploglossi infects Diploglossus fasciatus and Mabuya mabouya in Brazil, Panama, and Colombia. Meronts are elongate (6–20 × 3–8 μm), usually partially encircling the host cell nucleus, and produce 11–58 merozoites. Pigment forms a golden-yellow mass at one end. Gametocytes are ovoid to an elongate lentiform shape, 7–21 × 4–9 μm, seldom distinctly halteridial. A round vacuole may be present in about half of gametocytes. Pigment in both sexes comprises 20–30 scattered blackish granules. Sexual dimorphism is minimal. All types of erythroid cells are parasitized by meronts, from apparent stem cells to mature erythrocytes.
This parasite causes significant hypertrophy of host erythrocytes (up to 39-44%) and their nuclei (up to 62-65%) when infected by both meronts and gametocytes. A high percentage of host cells and nuclei are distorted and displaced, and enucleation can occur. Lysis of host cell nuclei is common.
FAQ about Reptilian Hemoparasites
What are the main types of hemoparasites in reptiles?
The main types of hemoparasites in reptiles include various species of Plasmodium, which are a type of protozoan parasite. These are often studied due to their prevalence and diverse morphological forms and host interactions, as detailed in this article.
How do Plasmodium parasites affect their reptile hosts?
Plasmodium parasites can have a range of effects on their reptile hosts, from causing hypertrophy (enlargement) or hypotrophy (reduction) of host red blood cells and their nuclei, to distorting and displacing these cells. Some species lead to anemia or reduced oxygen consumption, while others show minimal observable impact, depending on the parasite species and infection phase.
Are there specific reptile hosts for particular Plasmodium species?
Yes, Plasmodium species often exhibit host specificity. For example, P. tanzaniae and P. arachniformis are found in Chamaeleo werneri, while P. holaspi infects Holaspis guentheri. However, some species, like P. agamae and P. mabuiae, have broader host ranges within specific reptile families or genera, such as Agama or Mabuya species, respectively. These relationships highlight the intricate coevolution between parasites and their hosts.
What is the role of vectors in the life cycle of reptilian Plasmodium?
While not always fully understood for all reptilian Plasmodium species, vectors play a crucial role in transmitting the parasites between reptile hosts. For instance, Culicoides nubeculosus has been identified as a vector for P. agamae, undergoing sporogony in its midgut. Identifying vectors is key to understanding disease transmission and ecology. The presence of EE meronts in various tissues further suggests complex life cycles.
What are some unique morphological features of reptilian Plasmodium?
Reptilian Plasmodium species display fascinating morphological variations. Examples include the “arachnoid” appearance of P. arachniformis merozoites, the prominent masses of chromatin in P. holaspi gametocytes, or the nucleophilic (nucleus-loving) tendency of P. mabuiae and P. cordyli meronts. Pigment granule size, color, and distribution also vary significantly between species and life stages, providing diagnostic clues for identification.