Reproducibility of malaria sporozoite challenge model in humans for evaluating efficacy of vaccines and drugs: a systematic review

Background The development of novel malaria vaccines and antimalarial drugs is limited partly by emerging challenges to conduct field trials in malaria endemic areas, including unknown effects of existing immunity and a reported fall in malaria incidence. As a result, Controlled Human Malaria Infection (CHMI) has become an important approach for accelerated development of malarial vaccines and drugs. We conducted a systematic review of the literature to establish aggregate evidence on the reproducibility of a malaria sporozoite challenge model. Methods A systematic review of research articles published between 1990 and 2018 on efficacy testing of malaria vaccines and drugs using sporozoite challenge and sporozoite infectivity studies was conducted using Pubmed, Scopus, Embase and Cochrane Library, ClinicalTrials.gov and Trialtrove. The inclusion criteria were randomized and non-randomized, controlled or open-label trials using P. falciparum or P. vivax sporozoite challenges. The data were extracted from articles using standardized data extraction forms and descriptive analysis was performed for evidence synthesis. The endpoints considered were infectivity, prepatent period, parasitemia and safety of sporozoite challenge. Results Seventy CHMI trials conducted with a total of 2329 adult healthy volunteers were used for analysis. CHMI was induced by bites of mosquitoes infected with P. falciparum or P. vivax in 52 trials and by direct venous inoculation of P. falciparum sporozoites (PfSPZ challenge) in 18 trials. Inoculation with P. falciparum-infected mosquitoes produced 100% infectivity in 40 studies and the mean/median prepatent period assessed by thick blood smear (TBS) microscopy was ≤ 12 days in 24 studies. On the other hand, out of 12 infectivity studies conducted using PfSPZ challenge, 100% infection rate was reproduced in 9 studies with a mean or median prepatent period of 11 to 15.3 days as assessed by TBS and 6.8 to 12.6 days by PCR. The safety profile of P. falciparum and P.vivax CHMI was characterized by consistent features of malaria infection. Conclusion There is ample evidence on consistency of P. falciparum CHMI models in terms of infectivity and safety endpoints, which supports applicability of CHMI in vaccine and drug development. PfSPZ challenge appears more feasible for African trials based on current evidence of safety and efficacy.

DISTRIBUTION OF PLASMODIUM PARASITES CAUSING MALARIA AMONG LOCAL CHICKENS IN SALAHUDDIN PROVINCE , IRAQ.

This study included two stages, the first one was as epidemiological study of malaria in the local chickens of variuos areas in Salahuddin province the infection rate was 3.16 % out of 433 samples taken. There was different blood stages of the parasite which are represented by trophzoites, schizonts and to less extent gametocytes. The second stage was the experimental study,which showed the ability of induction of infection (subinoculation technique). Prepatent period was represented by the presence of trophozoites m schizonts and gametocytes. The most important clinical signs was partial paralysis , dullness and emaciation. The pathological changes showed congestion and enlargement of liver and spleen. congestion of brain with absence of exo-erythrocytic mild lymphocytosis in the infected group. it was concluded the ability of diagnosis of avian malaria using human malaria antigen by the indirect fluorescence antibody technique.

Highly diluted medication reduces tissue parasitism and inflammation in mice infected with Trypanosoma cruzi

Background: The search for new therapeutic approaches with fewer side effects and better treatment efficacy to the Chagas Disease has been a major challenge. Aim: To evaluate the effects of Kalium causticum, Conium maculatum, and Lycopodium clavatum 13 cH in mice inoculated with the Y strain of Trypanosoma cruzi. Materials and methods: In a blind, controlled, randomized study, 102 male Swiss mice, eight weeks old, were inoculated with 1,400 trypomastigotes of the Y strain of T. cruzi and distributed into the following groups: CI (treated with 7% hydroalcoholic solution), Ca (treated with Kalium causticum 13cH), Co (treated with Conium maculatum 13cH), and Ly (treated with Lycopodium clavatum 13cH). The medicines were selected by three homeopaths using Lince Expert System Software (Albuquerque, NM, USA), considering the behavioral characteristics of the mice. The treatments were performed 48 hours before and 48, 96, and 144 hours after infection [1]. The following parameters were evaluated: infectivity, prepatent period, parasitemia peak, total parasitemia, tissue tropism, inflammatory infiltrate, and survival. Results: The prepatent period was greater in the Ly group than in the CI group (p = 0.02). The number of trypomastigotes on the 8th day after infection was lower in the Ca group than in the CI group (p < 0.05). Total parasitemia was significantly lower in the Ca, Co, and Ly groups than in the CI group. On the 12th day after infection, the Ca, Co, and Ly groups had fewer nests of amastigotes and amastigotes/nest in the heart than the CI group (p < 0.05) (Figure-I). A decrease in the number of nests and amastigotes in the intestine were observed in the Ly group compared with the CI group (p < 0.05). In the liver (day 12), Ly significantly prevented the formation of inflammatory foci compared with the other groups. In muscle, Co and Ly decreased the formation of inflammatory foci compared with CI (p < 0.05). Ly afforded greater animal survival compared with CI, Ca, and Co (p < 0.05). The animals in the Co group died prematurely compared with the CI group (p = 0.031). (Figure-II) Conclusion: All of the experimental homeopathic medications with 13cH dynamization studied herein reduced the parasite peak and total parasitemia. Ly had significantly more benefits in the treatment of mice infected with T. cruzi, reducing the number of blood parasites, amastigotes nests in tissue and the number of amastigotes per nest, resulting in the increasing animal survival. The data may contribute to changes in management strategies in individuals with Chagas disease.

Pathogenicity of Philippine and Indonesian Trypanosoma evansi Isolates in Mice and Their Responses to Trypanocides

Pathogenicity of 10 isolates of <em>T. evansi</em> collected from Mindanao, Philippines, and one isolate from East Java, Indonesia was determined and compared. The susceptibility of these isolates against diminazene aceturate, melarsomine dihydrochloride, suramin and quinapyramine sulphate/chloride was also tested. Twenty-five mice were infected intraperitoneally with each isolate and 20 were treated with the 4 drugs (5 mice/drug) while 5 infected and 7 uninfected mice served as infected-untreated and uninfected controls, respectively. Treatment was carried out 24 hours post-infection and parasitemia was monitored for 35 days. Mice infected with Philippine isolates significantly died earlier (5-11 days) than those infected with the Indonesian isolate (14-16 days). The prepatent period for Philippine isolates (3-8 days) was significantly shorter than the Indonesian strain (11-13 days). Trypanosomes were not observed in the blood of mice infected with any of the Philippine isolates when treated with quinapyramine sulphate/chloride, melarsomine dihydrochloride or suramin. Two of 10 mice infected with either C4 or A9 Philippine isolates and treated with diminazene aceturate had parasitemia on days 29 and 31, respectively. It is concluded that isolates of <em>T. evansi</em> from Mindanao, Philippines, are more pathogenic than the isolate from East Java, Indonesia. This study also indicated that quinapyramine sulphate/chloride, melarsomine dihydrochloride and suramin are effective against these <em>T. evansi</em> isolates from Mindanao, Philippines and East Java, Indonesia, while two of the Mindanao isolates are resistant to diminazene. This information is valuable in the enhancement of the control strategy against surra in the Philippines and Indonesia.

Cryptosporidium myocastoris n. sp. (Apicomplexa: Cryptosporidiidae), the Species Adapted to the Nutria (Myocastor coypus)

Cryptosporidium spp., common parasites of vertebrates, remain poorly studied in wildlife. This study describes the novel Cryptosporidium species adapted to nutrias (Myocastor coypus). A total of 150 faecal samples of feral nutria were collected from locations in the Czech Republic and Slovakia and examined for Cryptosporidium spp. oocysts and specific DNA at the SSU, actin, HSP70, and gp60 loci. Molecular analyses revealed the presence of C. parvum (n = 1), C. ubiquitum subtype family XIId (n = 5) and Cryptosporidium myocastoris n. sp. XXIIa (n = 2), and XXIIb (n = 3). Only nutrias positive for C. myocastoris shed microscopically detectable oocysts, which measured 4.8–5.2 × 4.7–5.0 µm, and oocysts were infectious for experimentally infected nutrias with a prepatent period of 5–6 days, although not for mice, gerbils, or chickens. The infection was localised in jejunum and ileum without observable macroscopic changes. The microvilli adjacent to attached stages responded by elongating. Clinical signs were not observed in naturally or experimentally infected nutrias. Phylogenetic analyses at SSU, actin, and HSP70 loci demonstrated that C. myocastoris n. sp. is distinct from other valid Cryptosporidium species.

The impact of maturity on the ability of Eimeria acervulina and Eimeria meleagrimitis oocysts to sporulate

The sporulation of oocysts of Eimeria that infect poultry is known to be under the influence of environmental conditions, including temperature, oxygen supply, and moisture. However, even when these conditions are optimal, the level of sporulation can remain low. The effect of oocyst maturity on their ability to sporulate was investigated for two species of Eimeria: E. acervulina of chickens, and E. meleagrimitis of turkeys. After oral infection of birds, oocysts were collected at their production site in the intestine at different times around the prepatent period. The percentage of sporulation was determined by observation of 100 oocysts for each sample. With E. acervulina, it was observed that sporulation depended on the time of collection of the oocysts in the intestine, and that it increased with aging oocysts (from 5% to 40% globally in 8 h). With E. meleagrimitis, sporulation remained low with oocysts collected in the duodenum (below 20%), but oocysts collected in the midgut and in the lower intestine sporulated more efficiently (around 80%) than oocysts collected in the duodenum at the same time. One explanation for these results is the assumption that oocysts may be produced before fertilization, and that microgametes have not yet fertilized the newly produced oocysts. As time goes on, more oocysts would be fertilized, locally in the duodenum for E. acervulina, and descending along the gut for E. meleagrimitis. This hypothesis needs to be investigated further, but it could lead to new approaches to control these parasites by targeting the microgametes.

Pathogenicity of trypanosomes in relation to 1 drug sensitivity: comparative studies between a drug-sensitive and drug-resistant Trypanosoma congolense strain in murine-and bovine model

Background: Indiscriminate exposure of Trypanosoma congolense and other trypanosomes to trypanocides have led to emergence of resistant strains, which increasingly undermine the control efforts against tsetse transmitted animal trypanosomosis. Despite the increasing trend of resistance, no studies have conducted to assess whether or not drug sensitivity affects the pathogenicity of T. congolense and other predominant species. Methods: We compared the pathogenicity of two strains of trypanosomes: drug-sensitive Trypanosoma congolense -Mikese and drug-resistant T. congolense Mbagala. These strains were isolated from cattle at Mikese, Morogoro region and Mbagala, Dar es Salaam region, Tanzania, respectively. Experimental mice and cattle were infected with either tryapnosomes and monitored for rectal temperature, prepatent period, parasitemia, packed cell volume (PCV), survival and clinical manifestations. Drug sensitivity status of either strains was re-confirmed before pathogenicity testing. Results: Mean rectal temperature was higher in mice infected with T. congolense -sensitive strain (p=0.049, 95% CI= 0.003-1.13). Mean prepatent period of resistant strain in mice and cattle was shorter than that of sensitive strain. The mean level of parasitemia was significantly higher in resistant- (7.5±0.8) than in sensitive-strain (6.5±0.8) (p<0.001, 95% CI= -1.28 to -0.68). Mice infected with resistant strain were relatively dull and lethargic compared to those infected with sensitive strain. The decline PCV was higher in cattle infected with sensitive- strain than resistant-strain (p=0.041, 95% CI, -6.97 to -0.17). Conclusion: Pathogenicity of the two Trypanosoma congolense strains varied significantly across host species. The resistant strain was highly pathogenic in mice and less so in cattle. Contrarily, the sensitive strain was highly pathogenic to cattle and less so to mice. As such, this study emphasizes variations on the pathways by which different trypanosomes act upon the host; thus warranting subsequent studies using large number of experimental animals, preferentially cattle, in view of reflecting the field situation.

Promastigote secretory gel from natural and unnatural sand fly vectors exacerbate Leishmania major and Leishmania tropica cutaneous leishmaniasis in mice

Leishmania rely heavily on glycans to complete their digenetic life cycle in both mammalian and phlebotomine sand fly hosts. Leishmania promastigotes secrete a proteophosphoglycan-rich gel (Promastigote Secretory Gel, PSG) that is regurgitated during transmission and can exacerbate infection in the skin. Here we explored the role of PSG from natural Leishmania-sand fly vector combinations by obtaining PSG from Leishmania (L.) major-infected Phlebotomus (P.) papatasi and P. duboscqi and L. tropica-infected P. arabicus. We found that, in addition to the vector's saliva, the PSG from L. major and L. tropica potently exacerbated cutaneous infection in BALB/c mice, improved the probability of developing a patent cutaneous lesion, parasite growth and the evolution of the lesion. Of note, the presence of PSG in the inoculum more than halved the prepatent period of cutaneous L. tropica infection from an average of 32 weeks to 13 weeks. In addition, L. major and L. tropica PSG extracted from the permissive experimental vector, Lutzomyia (Lu.) longipalpis, also exacerbated infections in mice. These results reinforce and extend the hypothesis that PSG is an important and evolutionarily conserved component of Leishmania infection that can be used to facilitate experimental infection for drug and vaccine screening.

Gametogony of Eimeria macusaniensis Guerrero, Hernandez, Bazalar and Alva, 1971 in llama (Lama glama)

Camelids (llama, alpaca, vicunãs, guanacos) are important for the economy of South America and Eimeria infections are an important cause of mortality in camelids. Of the six species of Eimeria in camelids, Eimeria macusaniensis, considered the most pathogenic, is distinctive; its oocysts are the largest among all Eimeria species in animals, its prepatent period is more than 1 month, and its oocysts have been found in mummies from prehistoric times. Although, E. macusaniensis gametogonic stages are found associated with enteritis in naturally infected camelids, the schizogonic stages are unknown and clinical disease has been reported in some camelids with no oocysts in feces. Described herein are morphological details of gametogonic development and oocyst formation of E. macusaniensis in a naturally infected llama (Lama lama), solely infected with this parasite. Microgamonts, macrogamonts and oocysts were located in large (up to 300 µm diameter) parasitophorous vacuoles of enterocytes in the ileum. Schizonts were not found. Review of previous reports suggests that multinucleated microgamonts have been mistaken for schizonts. Gametogonic development described in the present study can serve as a guide for differential diagnosis of Eimeria species in the histological sections of intestines.