Patent Parasitemia Research Articles

Reduced responsiveness of the hypothalamic-pituitary-adrenal axis in Boran (Bos inducus) cattle infected with Trypanosoma congolense.

The response of the pituitary-adrenal axis to corticotrophin-releasing hormone (CRH) and the adrenal response to adrenocorticotrophin hormone (ACTH) stimulation were studied during infection of Boran (Bos indicus) cattle with Trypanosoma congolense. For CRH, 15 animals were challenged during preinfection and infection phases, while for ACTH 10 animals were challenged during pre-infection, infection and post-treatment phases of the experiments. The axis showed a reduced responsiveness after CRH challenge during patent parasitaemia, manifested by low (p < 0.05) plasma ACTH and cortisol concentration as compared to the pre-infection CRH challenge concentrations. Cortisol concentration after ACTH challenge during pre-infection, infection and post-treatment phases did not differ. The reduced pituitary-adrenal response to CRH challenge and the normal adrenal response to ACTH challenge found during trypanosomiasis indicates pituitary dysfunction due to infection.

Antibody patterns in rabbits showing different levels of susceptibility to an experimental Trypanosoma evansi infection

Using SDS-PAGE and Western blotting, the antibody spectrum of rabbits infected with Trypanosoma evansi to homologous T. evansi antigens was monitored. Animals that developed parasitaemia later or had lower levels of parasitaemia as the infection progressed were considered to have a degree of resistance to the infection. Sera of these resistant animals recognised the T. evansi antigens earlier and subsequently identified more antigens than their susceptible counterparts. The susceptible animals developed patent parasitaemia earlier and had higher parasite counts as the infection progressed, and their sera recognised T. evansi antigens later with fewer parasite components labelled during the course of the infection. These observations demonstrate clear differences between animals in response to T. evansi infections. Selection of T. evansi-tolerant animals on an individual basis may be possible as has been suggested for other trypanosome species.

Follow-up of patent and subpatent parasitemias and development of muscular lesions in mice inoculated with very small numbers of Trypanosoma cruzi

A sequential analysis of patent and subpatent parasitemias, mortality, and histopathology during acute Chagas' disease experimentally produced by inoculation of 10 or 100 bloodstream forms of Trypanosoma cruzi Y strain in susceptible mice was carried out. Parasites were searched for comparatively using three different methods: direct counting, Ficoll-MI density flotation, and hemoculture. Ficoll-MI density flotation promptly discriminated with high reproducibility subpatent parasitemic states not detected in the blood samples analyzed by direct counting. Despite the high proportion of supposedly uninfected animals and depending on the postinfection time, the majority of the mice had bloodstream parasites at the subpatent level detected by Ficoll-MI, and all of them had muscular lesions during the acute phase. All Ficoll-MI-negative blood samples from infected mice were also negative by hemoculture. Normal mouse blood purposely contaminated with parasite quantities ranging from 200 to 2000/ml was tested comparatively by density flotation and hemoculture and showed frequencies of reisolation varying from 25 to 100%. Overall, these data showed that inoculum as low as 10 infective forms of Y strain is able to induce acute Chagas' disease in susceptible mice and that a subpatent parasitemic state of 600–1000 forms/ml is a common finding. The use of Ficoll-MI to detect subpatent parasitemia is discussed.

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.

Relationships between trypanosome infection measured by antigen detection enzyme immunoassays, anaemia and growth in trypanotolerant N'Dama cattle

Relationsips were evaluated between trypanosome infection as measured by antigen detection enzyme immunoassays (antigen ELISA), anaemia as determined by average packed red cell volume (PCV), and animal performance as assessed by daily weight gain in 99 N'Dama cattle in Gabon exposed to natural tsetse challenge at 11.5 months of age and recorded 14 times over a 13 week period. Approximately half the animals were found to be infected for an average of five of the 14 times that they were examined: 38% with Trypanosoma congolense, 13% with Trypanosoma vivax and 49% with a mixed infection. Trypanosoma congolense infections had significant deleterious effects on animal growth, while T. vivax infections did not. Animals found on several occasions to be infected with T. congolense had significantly lower PCV values than those demonstrated to be infected on fewer occasions. No relationship was found between mean optical density (OD) values in antigen ELISA and PCV values. Animals capable of maintaining PCV values, even when antigen ELISA positive on a high number of occasions, grew at the same rate as uninfected animals. Animals that could not maintain PCV values when infected had poorer growth. Antigen ELISA has the potential to increase the efficiency of selection of trypanotolerant N'Dama cattle under tsetse challenge in the field, in three main ways. (1) Accurate identification of trypanosome species, especially in mixed species infections, clarifies relations between infection, anaemia and animal performance. (2) Detection of animals antigenaemic without patent parasitaemia could allow individuals with superior ability to control trypanosome infection to be identified. (3) More accurate measurement of the proportion of time an animal is infected allows more accurate evaluation of its anaemia control capability.

Biological characterization of Trypanosoma cruzi strains from different zymodemes and schizodemes

The development in C3H mice of thirteen strains of Trypanosoma cruzi belonging to different zymodemes and schizodemes was studied. Host mortality, virulence, histiotropism, parasitemia and polymorphism of the parasites were recorded. The strains were grouped into: a) high virulence--causing 100% mortality and characterized by predominance of very broad trypomastigotes in the bloodstream at the end of infection; b) medium virulence--causing no mortality and with a predominance of broad trypomastigotes; c) low virulence--causing no mortality with blood forms not described due to the very low parasitemia. During 18 months maintenance the parasitemia curves were kept constant for all strains except one. A direct correlation between either zymodeme or schizodeme and experimental biological properties of T. cruzi strains was not found. However, the parasitemia was subpatent and patent for strains from zymodeme C and the others respectively. Furthermore the high virulence seems to be related to one of two schizodemes found within zymodeme B strains. All strains presenting patent parasitemia independent of shizodeme and zymodeme showed a myotropism towards heart and skeletal muscle with variable inflammatory intensity. The present study confirmed the heterogeneity found by isoenzyme and k-DNA patterns among the strains of T. cruzi isolated from chagasic patients in Bambuí, Minas Gerais State, Brasil.

Longitudinal study of seroreactivities to Pf 155/RESA and its repetitive sequences in small children from a holoendemic area of Liberia

The seroreactivities to Pf155/RESA antigen and to three oligopeptides (EENV)2, EENVEHDA and K(DDEHVEEPTVA)2, which constitute repeat subunits of the RESA molecule, were investigated between 1980 and 1986 in two cohorts of children (n = 114) with and without monthly chemosuppression (pulsed reduction of parasite load) against malaria from six months to five years of age during development of protective immunity. Serum samples were collected first at half-yearly and then yearly intervals. Positive immunofluorescence against Pf155/RESA (EMIF) was only found in 24% of the samples. The children with chemosuppression were more often seropositive (30%) than the non prophylactic children (17%). This was in contrast to the seroreactivity against crude parasitic antigens which was highest in the non prophylactic children. In these children, there was a general decrease of EMIF titres around two years of age. Immunosuppression by chronic parasitaemia may be suggested as a reason for this. ELISA seroreactivity was found against one, two or three oligopeptides in all children with high EMIF titres (greater than 250) although (EENV)2 appeared to best correlate (92%) with the EMIF seropositivity. While EMIF seropositivity only showed partial correlation to immunoprotection against patent parasitaemia in the non prophylactic children, the individual profiles of the seroreactivities to the different specific epitopes of the Pf155/RESA molecule and their relevance with regards to protective immunity to malaria need to be investigated further.

Short-Tailed Shrews as Reservoirs of the Agents of Lyme Disease and Human Babesiosis

To determine whether short-tailed shrews (Blarina brevicauda) serve as reservoir hosts for the Lyme disease spirochete (Borrelia burgdorferi) and the agent of human babesiosis (Babesia microti), we examined nymphal ticks that had fed as larvae on shrews collected from 3 enzootic sites in coastal Massachusetts for evidence of infection by either or both of these agents. Xenodiagnosis indicated that 11 of 14 shrews were infected by B. burgdorferi. One of 3 piroplasm-infected shrews also infected ticks with B. microti. In a site where the piroplasm is endemic, 11 of 17 shrews showed patent parasitemias by thin blood smears. Of these, 4 had parasitemias exceeding 40%. Few immature ticks infested shrews, however, suggesting that B. brevicauda, although abundant in some endemic sites and serving as a competent reservoir, would contribute minimally to the population of infected nymphs.

Experimental chagas' disease in rhesus monkeys. I. Clinical parasitological, hematological and anatomo-pathological studies in the acute and indeterminate phase of the disease

Rhesus monkeys (Macaca mulatta) were infected subcutaneously with 1.0 x 10(4) to 1.5 x 10(4) metacyclic trypomastigotes of Trypanosoma cruzi (Colombian strain). Parasitological and immunological parameters were evaluated in these animals for periods of 1 month to over 3 years. A chagoma was observed between the 3rd and the 13th day after infection (a.i.) and patent parasitaemia between the 13th and 59th day a.i.. Thereafter, parasites were demonstrated only by haemoculture and/or xenodiagnosis. Circulating specific IgM and IgG antibodies were observed as early as in the 2nd week a.i. IgG levels persisted until the end of the experiment, but IgM antibodies were detectable nine months a.i. Haematological alterations comprised leucocytosis and lymphocytosis. Electrocardiographic alterations were minor and transient, similar to those observed in non-lethal human acute Chagas' myocarditis. Myocarditis and myositis, characterized by multiple foci of lympho-histiocyte inflammatory infiltrate, were present in monkeys sacrificed on the 41st, 70th and 76th day but not in the animal sacrificed 3 years and 3 months a. i.. The results suggest that Chagas' disease in rhesus monkeys reproduces the acute and indeterminate phases of human Chagas' disease.

Infecção natural das glândulas anais de gambás (Didelphis albiventris) pelo Trypanosoma cruzi no município de Bambuí - MG

De 87 gambás, Didelphis albiventris, capturados na região de Bambuí (MG), 32 (36,7%) estavam infectados pelo Trypanosoma cruzi. Os índices de infecção foram 34,9%, 81,8% e 7,7%, respectivamente, para animais capturados em ambiente silvestre, peridomiciliar rural e periodomiciliar urbano. Em 20 gambás infectados as glândulas anais foram examinadas repetidamente e apenas um (5%) animal (GA09) apresentou exame positivo. Foram positivos 7 dos 17 exames a fresco da secreção glandular desta animal ao longo de 18 meses. Material destas glândulas produziu parasitemia patente em gambás e infecção subpatente em camundongos. A análise isoenzimática realizada com amostras de T. cruzi do GA09, obtidas via hemocultura, xenodiagnóstico e glândulas anais demonstraram pertencerem rigorosamente ao mesmo Zimodema semelhante ao Zimodema Z1. As observações mostram que a infecção das glândulas anias pelo T. cruzi em gambás naturalmente infectados da região de Bambuí é baixa.

Plasmodium falciparum incidence and patency in a high seasonal transmission area of Burkina Faso

Using a mathematical model P. falciparum transition rates were calculated from the parasitological data collected from children of 2 villages of a high and seasonal transmission area in Burkina Faso (West Africa). During the rainy season, patent parasitaemia appeared every 40 to 60 d and was present for 60d approximately. The significance of these values is discussed.

Protective immunity to malaria: studies with cloned lines of Plasmodium chabaudi chabaudi in CBA/Ca mice. III. Protective and suppressive responses induced by immunization with purified antigens.

The protective effect of affinity purified antigen has been investigated in an experimental model for malaria which shows a well marked recrudescence of parasitaemia, a feature of the disease in man. A monoclonal antibody (MoAb) recognizing an epitope common to two genetically distinct cloned lines of Plasmodium chabaudi (AS and CB), was used to purify a Mr250,000 polymorphic schizont antigen (PSA) from these parasites. The purified preparations were then examined for the presence of specific and cross-reactive epitopes by immunoprecipitation with a panel of MoAb raised against P. chabaudi AS. When tested previously on smears of parasitized blood by immunofluorescence, or against lysates of parasitized erythrocytes by immunoprecipitation, most of these MoAb had been found to be AS specific. When either AS or CB affinity purified Mr250,000 PSA was used as the target, these same MoAb immunoprecipitated both antigens, and in some cases, a number of associated polypeptides (AP) which copurify with the Mr250,000 PSA. Subsequently, mice were immunized with either the purified AS or CB antigens in Freund's complete adjuvant (FCA). Prechallenge sera were compared by indirect immunofluorescence and immunoprecipitation. Sera from mice immunized with AS antigen reacted strongly with AS and cross-reacted with CB parasite preparations. Pre-challenge serum from CB antigen immunized mice reacted well with CB, but only faintly with AS preparations. In mice immunized with the AS antigen and then challenged with either AS or CB parasites, the initial parasitaemias were delayed in appearance and the height of the peak parasitaemia reduced, an effect which was most pronounced after challenge with homologous parasites. Only homologous challenge of the mice immunized with CB antigen produced statistically significant modification of the initial parasitaemia. In the immunized mice challenged with homologous parasites, the delayed appearance and slightly reduced peak of the primary parasitaemia was associated with delayed resolution of the patent parasitaemia and significant enhancement of the recrudescence.

Trypanosoma congolense: Lack of correlation between the resistance of cattle subjected to experimental cyclic infection or to field challenge

Twelve male cattle of the Baoulé breed were exposed to natural trypanosome challenge in an area of high Glossina density, to characterize them as trypanoresistant or trypanosensitive. Weekly blood samples were taken for the determination of parasitemia and packed cell volume, as a measure of anemia. Seven Zebu cattle were also exposed to challenge at the same time. The Zebu proved to be trypanosensitive with high parasitemia, pronounced anemia and died or were drug treated in extremis. Five Baoulé were as sensitive as the Zebu while 7 others were trypanoresistant since they showed little or no patent parasitemia, only mild transient anemia and survived in good condition. The 12 Baoulé were allowed to recover from challenge in the field and along with 7 Zebu were subjected to experimental fly challenge in fly-proof accommodation. Glossina morsitans submorsitans infected with a clone of Trypanosoma congolense derived from the stock Serengeti/71/STIB/212 were allowed to engorge on the shaven flanks of tranquilized animals. All animals showed persistant parasitemia for at least 7 weeks, including all the Baoulé resistent to natural challenge. Two Baoulé, one resistant and one sensitive to natural challenge, and 4 7 Zebu appeared unable to control parasitemia, had severe anemia, and were drug treated in extremis. The remaining Baoulé, 6 resistant and 4 sensitive, appeared to be undergoing spontaneous cure by Week 9–10, as did 3 7 Zebu. In Zebu, anemia was as pronounced as under natural challenge. Three resistant Baoulé maintained packed cell volume above 30 as under field challenge but the others showed marked anemia. On the contrary, 4 sensitive Baoulé showed only slight anemia after artificial fly challenge. Clearly there was no correlation between parasitemia, anemia, and disease syndrome in cattle subjected to experimental cyclic infection or exposed to natural trypanosome challenge.

The role of antibody in natural resistance to African trypanosomiasis

The nature and usefulness of trypanoresistance in West African Baoule cattle was studied by exposing animals in areas of high Glossina density. Under such conditions, Zebu and some Baoule died soon with high parasitaemia while resistant Baoule showed little patent parasitemia, almost no anaemia and thrived. Subsequently the role that specific antibody may play in such traypanoresistance was analyzed. In the first instance we examined protective antibody titres during T. congolense infection of inbred mice strains, comparing results obtained in trypanosome-mouse combinations where the host controls parasitemia and survives with those obtained when the host fails to control parasitemia and dies. We then attempted to extend these observations to cattle by following the disease course and appearance of neutralizing antibodies in animals of known sensitivity to natural Glossina challenges, following artificial challenge with T. congolense infected Glossina .

The effect of mosquito transmission of antigenic variants of Plasmodium chabaudi

Plasmodium chabaudi AS strain in mice is characterized by an acute primary parasitaemia, and one or more less acute recrudescences. Previous work has shown, using a passive protection assay, that the recrudescent parasites are usually antigenically different from parasites of the parent population with which the mice were first infected. In this study the effect of mosquito transmission on the antigenic expression of recrudescent populations of P. chabaudi was examined. In the first experiments the recrudescent population which was antigenically different from the parent population was uncloned. After transmission through Anopheles stephensi the recrudescent population appeared to revert to an antigenic type similar to that of the parent population. In the second experiment clones from a recrudescent population were mosquito transmitted and again the parasites of the primary patent parasitaemia in the mice, bitten by the infected mosquitoes, had reverted to the parental type. It is suggested that antigenic variants of P. chabaudi AS strain may revert to a basic type after mosquito transmission.

Merozoite surface coat precursor protein completely protects Aotus monkeys against Plasmodium falciparum malaria.

Groups of Aotus (owl) monkeys were immunized with either the Plasmodium falciparum merozoite surface-coat precursor protein and its processing fragments or a complex of high molecular mass rhoptry proteins and challenged with a lethal infection of the homologous P. falciparum Uganda Palo Alto (FUP) strain. No patent parasitemia could be detected on thick blood films of monkeys immunized with the merozoite surface antigens; however, only one of three monkeys immunized with the rhoptry proteins was partially protected, while two required drug therapy. The experiment clearly demonstrates that the merozoite surface-coat precursor protein can completely protect Aotus monkeys against a lethal infection of the human malaria parasite.

Plasmodium yoelii: Induction of attenuated mutants by irradiation

When erythrocytic forms of Plasmodium yoelii nigeriensis, which is invariably fatal in mice, were exposed to X rays, the dose to reduce surviving parasites to one millionth was 100 gray (10 Krad). A suspension of 5 × 10 6 per ml of parasitized erythrocyte was irradiated at 100 gray, and 0.2 ml aliquots were inoculated into 22 mice. Eleven mice showed patent parasitemia, and in these the growth curves were less steep than that found in nonirradiated parasites. The infections of 8 mice of the 11 were self-resolving, and the attenuated feature of the parasites maintained following a limited number of blood passsages. The parasites were slowly growing even in nude mice and cause self-resolving infections in intact mice. BALB c mice immunized with the attenuated parasites were protected against subsequent challenge infections with the original virulent erythrocytic and sporogonic forms. These findings indicate that attenuated mutants of malaria parasites can be readily induced by this method.

Antigenic variation in Plasmodium chabaudi: analysis of parent and variant populations by cloning.

Nineteen of 22 recrudescent populations of Plasmodium chabaudi AS strain were found to be significantly less sensitive to the protective activity of pools of immune serum, than the parent population from which they were derived. The immune sera were collected from donor mice which had been infected with the parent population and had just reduced the patent primary parasitaemia to subpatent levels. Clones prepared from the parent population (which had previously been cloned) and recrudescent variant populations were tested for their sensitivity to the immune sera. It was found that all the clones from the parent population were sensitive to the immune sera but some were more sensitive than others and that a recrudescent variant population could include both sensitive and insensitive parasites. Two insensitive clones of the recrudescent population were found to be different from each other.

T-cell immunity in murine malaria: adoptive transfer of resistance to Plasmodium chabaudi adami in nude mice with splenic T cells.

Acute infections caused by the murine malarial parasite Plasmodium chabaudi adami are resolved by antibody-independent mechanisms of immunity. The fact that athymic nude mice developed high-grade unrelenting malaria and died when infected with this parasite suggested a significant role for T lymphocytes. Using adoptive transfer techniques, we demonstrated that spleen cells from either nonimmune or immune donor BALB/c mice eventually suppressed P. chabaudi adami infections in histocompatible recipient nude mice in a dose-dependent manner. Infections in recipients of "immune" spleen cells were less severe, demonstrating a depressed peak parasitemia and a shortened duration of patent infection, than was observed in recipients of normal spleen cells. Also, when sufficient numbers of immune spleen cells were transferred, the second wave of parasitemia (characteristic of this infection in nonimmune mice) failed to occur. T lymphocytes mediated protection in recipient mice, since T-cell-enriched, but not B-cell-enriched, spleen cell fractions suppressed P. chabaudi adami infections in nude mice. Protection was best achieved with T cells that bore the L3T4 phenotype. Patent parasitemias developed in all recipient mice, suggesting that the grafted cells did not limit parasite growth directly but achieved this end by activating other as yet unidentified inhibiting cell systems.

In vivo response of Plasmodium falciparum to different doses of chloroquine in semi-immune children in Liberia, West Africa.

The efficacy of different doses of chloroquine in suppressing patent parasitaemia was investigated in 326 children two to 12 years old, living in six villages with holoendemic malaria. The children were given single doses (2, 3, 5-7 or 9-12 mg base kg-1) or a standard treatment over three days (25 mg base kg-1). Parasite prevalences were recorded after one, two, three, four, six and eight weeks. Complete clearance of Plasmodium falciparum trophozoites (TC) by day 7 was achieved by a dosage of 9-12 mg kg-1. By probit analysis of log dose response, 50% clearance (TC50) was established at about 1.5 mg kg-1, whereas a TC95 required 5.5 mg kg-1. The reappearance of patent parasitaemia was dependent on the dose of chloroquine given and on malaria transmission. After the standard dose treatment, only one re-infection in 56 children appeared within 21 days despite high sporozoite inoculation rates in the area. The dosage of 9-12 mg kg-1 yielded a hundredfold reduction of mean parasite density in the children if calculated over a four-week period. It may represent a suitable monthly regimen in a malaria control scheme in a holoendemic area with high P. falciparum sensitivity to chloroquine.