Pathogenicity and chemotherapy of Plasmodium durae in experimentally infected domestic turkeys

Only 3 out of 8 South African isolates of Plasmodium durae used in 524 turkeys in 161 passages caused approximately 50% mortality, a further 3 produced approximately 10% mortality while 2 were found to be apathogenic. Exoerythrocytic schizonts were the main pathogenic stage. In most survivors the effect on mass gains was minimal. Twelve drugs currently available for use in poultry, as well as chloroquin phosphate, were tested for their activity against experimental infections with Plasmodium durae in domestic turkeys. While chloroquin phosphate showed a certain degree of effectivity, Amprolium, Amprolium + Ethopabate, Maduramycin, Toltrazuril, Metronidazole, Furazolidone, Enrofloxacin and Sulfamethoxypyridazine + Trimethoprim were ineffective. Halofuginone and Penta-Sulfa at a high dose had some protective effect. At high doses Sulfachloropyrazine protected from mortality without affecting the parasitaemia, while Sulfamonomethoxine suppressed parasitaemia without entirely protecting from mortality. From these data it is concluded that Halofuginone has a potential as possible chemoprophylactic. While a combination of Sulfamonomethoxine and Sulfachloropyrazine could be used in the treatment of outbreaks in the field.

A host-parasite list of the haematozoa of domestic poultry in sub-Saharan Africa and the isolation of Plasmodium durae Herman from turkeys and francolins in South Africa

An annotated host-parasite list of the blood parasites of domestic poultry in sub-Saharan Africa is presented. This list contains the haematozoa found in domestic waterfowl (ducks, geese and muscovies) and phasianids (turkey, fowl and peafowl). In South Africa Plasmodium durae was isolated from 4 out of 8 backyard turkeys, from 3 out of 26 Swainson's francolins and from 1 redwing francolin, but not from 20 helmeted guineafowls and 9 greywing francolins. This points at Swainson's and redwing francolins as being the main natural hosts of P. durae in South Africa. The increase in the period of prepatency after intramuscular subinoculation as compared with the intravenous route was found to correspond to that of a 1,000 fold dilution of an intravenous inoculum of parasitized blood. This delay was not due to an intervening cycle of exoerythrocytic schizogony, but to large numbers of the injected erythrocytes apparently not finding their way into the circulation of the new host.

Experimental transmission of murine malaria by the oral route

A total of 116 young male CD1 mice were orally inoculated with mouse blood; half of the animals received 0.2 ml of uninfected blood and the others were given 0.2 ml of Plasmodium berghei yoelii-infected blood in six experiments performed at different times. Almost 30% of the experimental mice acquired malaria as demonstrated by the observation of parasites in their blood. In no case were parasites found in the blood of control mice. Rodent malaria parasites may be transmitted to CD1 mice by the ingestion of mouse blood parasitized by P. b. yoelii. As far as we know, this study represents the first demonstration of oral transmission of murine malaria. Oral transmission studies in this mouse-Plasmodium model may produce very important information on the biology of the malaria parasites.

Plasmodium berghei: sporozoites are sensitive to human serum but not susceptible host serum

Human complement was activated by rodent malaria, Plasmodium berghei, sporozoites through the alternative pathway, as revealed by C3 deposition on sporozoites using the fluorescent antibody technique. Sporozoites exposed to fresh human serum decreased in infectivity to HepG2 cells, but those exposed to heated or C3-deficient human serum showed normal infectivity to HepG2 cells. In contrast, C3 deposition was not observed on the sporozoites treated with mouse or rat serum even in the presence of specific polyclonal anti-sporozoite antibody. However, following treatment with trypsin (250 micrograms/ml), 81% of salivary gland sporozoites and 49% of oocyst sporozoites became reactive with mouse serum, and reactive sporozoites deposited mouse C3 on their surface in the presence of 30 mM EGTA and 1 mM Mg2+ without antibody. Concomitantly some sporozoites lost reactivity to anti-circumsporozoite protein monoclonal antibody. These results suggest that P. berghei sporozoites possibly express surface molecules that regulate the complement activation pathway of susceptible hosts but not of nonhosts, and that the putative structures consist of protease-sensitive molecule(s) which are closely associated with the circumsporozoite protein.

Host association and the capacity of sand flies as vectors of lizard malaria in Panama

In this paper the capacity of sand flies (Lutzomyia) as vectors of parasites that cause malaria in anoles (Anolis limifrons) in the Zona de Canal, Panama was investigated. Inhabiting all study plots, often in local abundance, L. trinidadensis emerged as the principal candidate sand fly vector; the results of surveys did not suggest a likely mosquito vector. Although L. trinidadensis and infected anoles co-inhabited all plots, their abundances seemed unrelated. No evidence that sand flies parasitized anoles was uncovered. As anole activity patterns in daylight reciprocate with those of sand flies and at night anoles seem to avoid locations that sand flies frequent, anoles may evade sand fly bites altogether. Further, these sand flies occurred in close numerical and ecological association with Thecadactylus rapicauda, a reclusive moist forest gecko, often parasitizing these hosts in large numbers. Thus, sand flies lack capacity as vectors of malaria-causing parasites in central Panamanian anoles.

Susceptibility of Macaca fascicularis monkeys from Mauritius to different species of Plasmodium

Macaca fascicularis monkeys from Mauritius were shown to be susceptible via sporozoite inoculation to 7 species of Plasmodium (P. fragile, P. coatneyi, P. gonderi, P. inui, P. cynomolgi, P. knowlesi, and P. fieldi), indigenous to macaques in southeastern Asia. Four monkeys were sequentially infected with different species of Plasmodium to determine maximum and course of parasitemia. In 2 nonsplenectomized monkeys, P. fragile developed maximum parasite counts of only 134 and 155/microliters. For Plasmodium knowlesi, a parasite that is life-threatening to rhesus monkeys, maximum parasite counts were 4,278 and 7,440/microliters. Plasmodium coatneyi developed to what must be considered as moderate levels. After animals underwent splenectomy, parasite counts of P. coatneyi were 58,280, 89,094, 4,464, and 43,524/microliters. The maximum parasite counts for P. gonderi (13,508 and 21,576/microliters) and P. fieldi (1,767 and 17,836/microliters) were lower than would be expected in M. mulatta. In 2 monkeys that developed patent parasitemia with P. inui, the maximum parasite counts (95,046 and 728,748/microliters) indicated that this parasite may be the best adapted species for development in these animals once infection is established. Finally, the reinfection of 2 monkeys with P. cynomolgi suggested that some animals may be basically more resistant than others, whether splenectomized or not, to the production of high-density parasitemia.

Multiple alpha-globin genes in crab-eating macaques (Macaca fascicularis)

Alpha-globin genes in crab-eating macaques were found to be triplicated at high frequencies according to restriction-enzyme comparisons. The frequencies of triplicated alpha-globin genes in macaques originally from Malaysia and Indonesia were 0.432 and 0.275, respectively, while no triplication was found in individuals from either the Philippines or northern and central Thailand. Quadruplicated alpha-globin genes were also observed, at frequencies of 0.045 (Malaysia), 0.075 (Indonesia), and 0.021 (the Philippines). A single locus was detected in only one of 40 chromosomes from Indonesia (frequency 0.025).

Immune responses against sexual stages of Plasmodium vivax during human malarial infections in Sri Lanka

During natural infections of P. vivax malaria a variety of immune responses to the infection affect infectivity of the parasites to mosquitoes. Sexual stage antigens present in the blood stage parasites induce antibodies which may either enhance or suppress the infectivity of the sexual parasites to mosquitoes. Subsequent infections of P. vivax do not, unless occurring within less than 4 months, boost this response indicating a very short immune memory for the relevant antigens. Blood infection also results in the release of cytokines and other non-antibody factors which together can mediate death of the blood stage sexual parasites. These factors are associated with paroxysm in non-immune individuals. In individuals from an endemic area with age-acquired anti-disease immunity clinical symptoms are mild and the parasite killing factors are not induced.

[The nucleoprotein fraction of mouse serum in normal and pathological processes]

Analysis of the blood serum of healthy and infected with malaria plasmodium mice showed a steep rise in content of linear double-stranded DNA (0.2-0.5 and 2-15 gamma/ml, respectively). Some physico-chemical properties of serum DNA and a DNA-associated glycoprotein (M approximately 40 kDa) are determined.

[Analysis of the trypsin hydrolysate of a 40-kDa protein, found in the nucleoprotein of serum. Identification of it as alpha(1)-acidic glycoprotein (orosomucoid)]

From the tryptic hydrolysis of 40-kDa protein from the mouse blood serum thirty-four peptides were isolated by HPLC, of which complete and partial amino acid sequence was established for twenty-eight and six, respectively. On the basis of these data the protein is identified as the blood serum alpha 1-acid glycoprotein.

The Peruvian III strain of Plasmodium brasilianum in Saimiri sciureus boliviensis monkeys

A strain of Plasmodium brasilianum was isolated from a naturally infected Saimiri monkey from Peru and subsequently passaged to 21 splenectomized Saimiri sciureus boliviensis monkeys. Nine of 12 attempts to transmit infection by sporozoite inoculation were successful with prepatent periods ranging from 23 to 41 days. Gametocytes were infective to Anopheles freeborni, Anopheles stephensi, Anopheles dirus, Anopheles maculatus, and Anopheles gambiae mosquitoes. The strain demonstrated a high level of resistance to cure with chloroquine.

Virulence of lizard malaria: the evolutionary ecology of an ancient parasite-host association

The negative consequences of parasitic infection (virulence) were examined for two lizard malaria parasite-host associations: Plasmodium agamae and P. giganteum, parasites of the rainbow lizard, Agama agama, in Sierra Leone, West Africa; and P. mexicanum in the western fence lizard, Sceloporus occidentalis, in northern California. These malaria species vary greatly in their reproductive characteristics: P. agamae produces only 8 merozoites per schizont, P. giganteum yields over 100, and P. mexicanum an intermediate number. All three parasites appear to have had an ancient association with their host. In fence lizards, infection with malaria is associated with increased numbers of immature erythrocytes, decreased haemoglobin levels, decreased maximal oxygen consumption, and decreased running stamina. Not affected were numbers of erythrocytes, resting metabolic rate, and sprint running speed which is supported by anaerobic means in lizards. Infected male fence lizards had smaller testes, stored less fat in preparation for winter dormancy, were more often socially submissive and, unexpectedly, were more extravagantly coloured on the ventral surface (a sexually dimorphic trait) than non-infected males. Females also stored less fat and produced smaller clutches of eggs, a directly observed reduction in fitness. Infected fence lizards do not develop behavioural fevers. P. mexicanum appears to have broad thermal buffering abilities and thermal tolerance; the parasite's population growth was unaffected by experimental alterations in the lizard's body temperature. The data are less complete for A. agama, but infected lizards suffered similar haematological and physiological effects. Infected animals may be socially submissive because they appear to gather less insect prey, possibly a result of being forced into inferior territories. Infection does not reduce clutch size in rainbow lizards, but may lengthen the time between clutches. These results are compared with predictions emerging from several models of the evolution of parasite virulence. The lack of behavioural fevers in fence lizards may represent a physiological constraint by the lizards in evolving a thermal tolerance large enough to allow elimination of the parasite via fever. Such constraints may be important in determining the outcome of parasite-host coevolution. Some theory predicts low virulence in old parasite-host systems and higher virulence in parasites with greater reproductive output. However, in conflict with this argument, all three malarial species exhibited similar high costs to their hosts.

Saurian malaria in Kenya: epidemiological features of malarial infections in lizard populations of the West Pokot District

During investigations into the prevalence of malarial parasites among lizards in the West Pokot District in Kenya, 179 lizards comprising eight species were caught. Examination of the Giemsa-stained smears made from their blood showed that 34 lizards were infected with Plasmodium species. Fifteen lizards were infected with a single species of Plasmodium and 19 carried multiple infections, the maximum, in four lizards, was four species. There were 19 combinations of parasite infections. Seventeen Plasmodium species were identified, the commonest being P. icipeensis. Only two of the eight lizard species were infected: the skink Mabuya striata and the agamid Agama agama. Eight of the Plasmodium species infected both; another eight species infected M. striata only but three of these have been described from different lizard families elsewhere in Africa. P. robinsoni infected A. agama only, although it was first described from another lizard family in another part of Africa. The epidemiological significance of these results is discussed.

An ultrastructural study of the exoerythrocytic schizonts of Plasmodium cynomolgi and P. knowlesi in Macaca mulatta

Exoerythrocytic schizonts of Plasmodium cynomolgi and P. knowlesi were examined by electron microscopy in biopsy samples of primate livers. With maturity the parasitophorous vacuole membrane becomes highly sculptured by the addition of a discontinuous dense thickening, the distribution of which can be a distinguishing character between these two species. The parasitophorous vacuole membrane follows the contours of the parasite faithfully with a minimal surrounding vacuole. The marked destruction of the cytoplasm of the host hepatocyte by most of the parasites studied however gave the distinct, but erroneous, appearance of a large parasitophorous vacuole at the light microscope level. The mature parasite often exhibited a highly invaginated surface contour with the result that the cytoplasm of the host cell and parasite became intimately interdigitated, this interweaving is unlikely to be recognized in light microscopic studies.

Discovery of the pre-erythrocytic stages of a saurian malaria parasite, hypnozoites, and a possible mechanism for the maintenance of chronic infections throughout the life of the host

Re-examination of tissue sections from four Takydromus tachydromoides (Sauria: Lacertidae) naturally infected with Plasmodium sasai found liver parenchymal cells, containing uninucleate parasites which may correspond to the hypnozoite stage of primate malaria parasites, schizonts and segmenters in parenchymal cells, and hepatic macrophages which contained numerous schizonts. Following destaining of the original H&E and prolonged restaining with warm Giemsa stain, encysted schizonts, protected by a hyaline wall, were discovered in the connective tissue or capillary endothelium of lung, liver, brain, heart, pancreas, kidney, intestine wall, testis, and both intra- and intermuscularly in the femoral muscles. Unencysted schizonts in the pulmonary endothelium apparently represent the phanerozoic stages, which, following encystment in the various tissues, are recognized as a new stage in the life cycle of reptilian malarial parasites, the chronozoic schizonts. A hypothesis is presented to describe the life cycle of P. sasai, which may be characteristic of other saurian malaria parasites. It interprets the sequence of pre-erythrocytic stages found as follows: sporozoites enter hepatic parenchymal cells where some may become dormant as hypnozoites, and others form cryptozoic schizonts. The cryptozoites parasitize hepatic macrophages and form metacryptozoic schizonts. Metacryptozoites produce phanerozoic schizonts in the capillary endothelium and connective tissue of the lung and other organs. Phanerozoites and possibly metacryptozoites then invade the erythrocytes to begin the erythrocytic cycle. Some of the phanerozoites in endothelium, connective tissue and skeletal muscle become encysted as chronozoic schizonts, and their progeny, chronozoites, renew the erythrocytic cycle throughout the life of the host and produce seasonal relapses of gametocytemia, in spring, at the end of hibernation by the lizard.

The sex ratio of Plasmodium gametocytes

Sex ratio theory usually predicts an equilibrium sex ratio and equal proportions of males and females in a population, including the progenitors of the reproductive cells of protozoans. This proposal was tested with three species of malarial parasites of lizards, Plasmodium mexicanum of the western fence lizard, and P. agamae and P. giganteum of the African rainbow lizard, using single samples from naturally infected lizards, repeated samples from free-ranging lizards (P. mexicanum only), and repeated samples from laboratory maintained animals. Macrogametocytes were usually more abundant than microgametocytes, and were slightly larger, revealing a typically greater investment of resources by the progenitors of female reproductive cells. However, the proportion of microgametocytes varied among the three species and among infections within each species of Plasmodium. The sex ratio of gametocytes often remained constant within infections followed over time even if the absolute number of gametocytes was changing. However, the equilibrium sex ratio of gametocytes varied among those infections that had an unchanging microgametocyte proportion. Thus, although an equilibrium sex ratio apparently occurs for most infections, there appears to be no characteristic proportion of microgametocytes for any of the species. Potential explanations for this conflict with theory are presented.

Host diet in experimental rodent malaria: a variable which can compromise experimental design and interpretation

Over the past few years several experienced groups studying malaria have encountered significant problems with their particular rodent malaria-host system. This has involved, in some cases, periods during which the recovery of cryopreserved parasite stocks and growth of bloodstream parasites was markedly inhibited and, in other cases, periods of drastically increased mortality rates. The common factor linking these incidents was that they coincided with alterations in the experimental animal diet used. The inhibition of growth of cryopreserved stabilates or bloodstream parasites was abolished by supplementation with p-aminobenzoic acid (PABA) or by changing the diet used. Although the suppressive effects of diets lacking PABA on parasite growth have been known for over 30 years, the variation of PABA levels in modern laboratory animal feed concentrates is not well recognized. We have not established the exact cause of increased mortality, but it has been overcome by changing the diet used. We are documenting our experiences with this potential variable to forewarn workers in other laboratories of possible problems inherent in the use of different diets.

Experimental infections of Plasmodium yoelii nigeriensis in mice and rats, and hosts' reactions

In investigations into the course of infection of Plasmodium yoelii nigeriensis in rats and mice, it was found that adult mice, baby mice and baby rats were susceptible to the infection, while adult rats were totally refractive. The infection was rapidly fatal in baby and adult mice but was maintained with a low parasitaemia and tolerated by baby rats until the animals were 7 weeks old, after which they eradicated the infection totally. Although the adult rats did not exhibit any parasitaemia, there was a decrease in their haemoglobin and packed cell volume values. In adult mice, the haemoglobin and packed cell volume values were found to decrease with the increase in parasitaemia.

The use of a DNA probe for the differentiation of rodent malaria strains and species

A clone, PCsv4, derived from a partial genomic library of the rodent malaria Plasmodium chabaudi chabaudi AS strain, contains an insert which when used as a probe at low stringency in Southern blotting of genomic DNA from a variety of strains, subspecies and species of rodent malaria parasites, results in a pattern of hybridisation which is specific to each of the DNA samples used, thus providing an accurate method to define a rodent malaria line. The insert only hybridises to DNA derived from malaria parasites of rodent species. The insert also hybridises to a small number of RNA transcripts.

A nitrocellulose membrane-based ELISA for the detection of Plasmodium infections in mosquitos

A nitrocellulose (NC) membrane was evaluated as a solid-phase support for the detection of malaria-infected mosquitos using monoclonal antibodies (MAb) with a laboratory model based on Plasmodium inui and Anopheles dirus. MAbs produced against sporozoites of the N34 strain of P. inui, and selected by immunofluorescence assay and the circumsporozoite precipitin test, were used. A one-site indirect NC-ELISA that used unlabelled MAb and enzyme-labelled anti-mouse IgG was developed. Its sensitivity was about 200 sporozoites and it reliably detected one infected mosquito in a pool of 20. This indirect NC-ELISA has the advantage that it does not require direct conjugation of the MAb to an enzyme or biotin. In the direct one-site NC-ELISA, which is also reported, the relatively simple biotinylation procedure was an alternative to the enzyme- or radiolabelled MAbs. The NC-ELISAs were simple and rapid. Furthermore, the indirect NC-ELISA can be used to detect sporozoite antigen localized in various body sectors of mosquitos.

Plasmodium vivax malaria in the common marmoset, Callithrix jacchus: adaptation and host response to infection

Infection with Plasmodium vivax was established in splenectomized Callithrix jacchus marmosets by inoculation of parasitized blood from Aotus trivirgatus carrying the Vietnam Palo-Alto line of P. vivax. Subsequent blood passage through intact marmosets resulted in higher peak parasitaemias (about 1% of red cells infected) and the loss of stainable Schüffner's dots in infected cells. Primary infections with the adapted line were patent for 74 days or more, and induced both a substantial antibody response, as determined by indirect fluorescence, and some lymphocytosis, but no marked anaemia. Marmosets which had recovered from their primary infection (or in which it was drug-cured) suffered abbreviated patency with low-grade parasitaemia on re-infection.

Infection of Aotus vociferans (karyotype V) monkeys with different strains of Plasmodium vivax

Twenty splenectomized Aotus vociferans (karyotype V) monkeys were infected with strains of Plasmodium vivax from New Guinea, North Korea, Indonesia, El Salvador, and Honduras. Peak parasite densities ranged from 4,840 to 75,500 per mm3. Gametocytes infective to different species of mosquitoes were produced with all strains of P. vivax studied. Two transmissions of the Chesson strain of P. vivax were made by the intravenous inoculation of dissected sporozoites from An. dirus mosquitoes. Prepatent periods were 16 days.

Re-examination of earlier work on repetitive DNA and mosquito infectivity in rodent malaria

Previous results, relating mosquito infectivity to percentage of repetitive DNA in the genome of Plasmodia, are re-examined in the light of the finding that a parasite line used in the previous studies and classified as Plasmodium berghei NK65, was a mixed infection, where the major component appeared to be Plasmodium yoelii. This conclusion was reached through cloning and isoenzyme typing of different clones. Isoenzyme typing alone is not sufficiently sensitive to reveal contamination amounting to less than 20% in a mixture. Attention is drawn to the risk inherent in work with uncloned lines, where the proportions of species or sub-species present may vary according to line history and gametocyte viability.