[To what extent Africa can limit the impact of the COVID-19 pandemic?] / Jusqu'où l'Afrique peut-elle limiter l'impact de la pandémie de COVID-19 ?

Following the onset of the global COVID-19 pandemic and the alerts issued by the World Health Organization, for several months attention has been focused on Africa as a potentially severely endangered continent. A sizable number of African countries, mainly low and middle income, suffer from limited available resources, especially in critical care, and COVID-19 is liable to overwhelm their already fragile health systems. To effectively manage what is shaping up as a multidimensional crisis, the challenge unquestionably goes beyond the necessary upgrading of public health infrastructures. It is also a matter of anticipating and taking timely action with regard to factors that may mitigate the propagation of SARS-CoV2 and thereby cushion the shock of the pandemic on the African continent. While some of these factors are largely unmanageable (climate, geography…), several others (socio-cultural, religious, audio-visual, and potentially political…) could be more or less effectively dealt with by African governments and populations.

The effect of essential oils from Thymus broussonetii Boiss on transmission of Toxoplasma gondii cysts in mice.

In this study, we have evaluated the effect of essential oils of Thymus broussonetii Boiss, an endemic plant of Morocco in experimental transmission of Toxoplasma gondii cysts in mice. These oils were obtained by hydrodistillation and were administered to mice at 20 microg/animal orally at the time of infection and for several days thereafter. This resulted in total absence of intracerebral cysts in mice who received the essential oils signifying that these essential oils of thyme have a blocking effect on the appearance of the cysts. In addition, no abnormality was observed in the control mice who received the essential oils of thyme.

Study of prevalence and parasite load of Schistosoma haematobium in schoolchildren in the Rosso region, Mauritania.

This study assessed the prevalence of schistosomiasis among 307 schoolchildren aged from 7 to 17 years at various schools in four districts in the Rosso region. Hematuria was observed among 17.5% (54/307) and Schistosoma hematobium eggs were found among 15.6% (48/307). We observed the highest prevalence rates (P = 0.003) among schoolchildren in the districts of Breun (19.75% ± 0.09), Tounguen (18.66% ±0.08) and PK 7 (18.42 % ±0.08). The statistical analysis showed that the differences in the prevalence, hematuria rate, and parasite load did not differ significantly by the schoolchildren's age and sex (P > 0.05). Schoolchildren in Demeldek were significantly (P = 0.003) less infested (5.33% ± 0.11) than those in the other districts. The parasite load ranged from 6 to 15 eggs/10 ml of urine. The malacological investigations conducted at the water points of each village visited showed the presence of Bulinus truncatis, Bulinus forskalii, Lymnaea natalanis, Biomphalariae feifferi and Melanoides tuberculata. These results show that schistosomiasis poses a public health problem in the region. To eradicate this parasitosis, it will be necessary to conduct more detailed malacological studies and combine several types of preventive actions.

A technique for dating toxoplasmosis in pregnancy and comparison with the Vidas anti-toxoplasma IgG avidity test.

A comparative evaluation of 384 selected sera was performed using the Beckman Coulter Access and Abbott Axsym Toxo-IgG assays. The Axsym assay yields positive early results following infection, while the Access assay gives higher titres during chronic infection. The ratio between the two complementary tests, Axsym Toxo-IgG/Access Toxo-IgG (Ax/Ac), was compared with the Vidas anti-Toxoplasma IgG avidity index (AI). The Ax/Ac ratio decreased progressively as the time between infection and sampling increased. The mean Ax/Ac values (+/-SE) were 2.50 (+/-0.26), 2.14 (+/-0.13), 2.33 (+/-0.22), 1.34 (+/-0.09), 1.32 (+/-0.10), 0.92 (+/-0.08) and 0.74 (+/-0.07) for groups of sera sampled at 1, 2, 3, 4-5, 6-8, 9-12 and 13-24 months, respectively, after infection in pregnant women. These values were much smaller for cases with chronic infection (>24 months), i.e., 0.56 (+/-0.03), 0.44 (+/-0.04) and 0.53 (+/-0.04), respectively, for pregnant women and immunodepressed patients with and without reactivation. Taking a ratio of 1 as a threshold for recent infection, the patients in the groups sampled at 1, 2 and 3 months had Ax/Ac ratios >1 in 49/50 (98%), 53/55 (96.4%) and 36/36 (100%) cases, respectively. Thus, an Ax/Ac ratio of <1 in serum from a pregnant woman allows a recent infection (<3 months) to be excluded. This technique has the advantage of yielding positive results that develop much more rapidly than the AI, thereby helping to reassure large numbers of pregnant women and avoiding costly and unnecessary prophylactic treatment and follow-up.

[Study of prevalence of Toxoplasma gondii oocysts in the cats of Nouakchott]. / Étude de la prévalence des oocystes de Toxoplasma gondii chez le chat à Nouakchott.

The aim of the work was to evaluate the prevalence of Toxoplasma gondii oocyst shedding on a sample of 100 cats in five districts of Nouakchott, Mauritania. The faecal flotation method revealed that 23% ± 0.08 of cats which underwent the test excreted oocysts and the prevalence was influenced by age and sex. Excretion rates were significantly higher in neighborhoods of Basra (27.8 ± 0.2), Elmina (25 ± 0.13) and Netegue (20 ± 0.35). The average parasite number was less than 5 oocysts/5 g faeces. Hence, the results suggest that cats have an important role in the transmission of the zoonosis in Nouakchott.

Seroprevalence of T. gondii in sheep from Marrakech, Morocco.

Toxoplasma gondii is a ubiquitous intracellular protozoan parasite transmitted by food. Concerning this parasite, there are few studies done in Morocco. In this study, 261 sera from sheep intended for consumption in Marrakech were subjected to the Toxoplasma ELISA based serology test for the detection of anti-T. gondii specific IgG confirming a past infection. Of the total tested 72 (27.6%) sera were positive for IgG. This result shows that the seroprevalence approaches the world average and is similar to what is found in other cities of Morocco. This has prompted us to investigate other animal species in the region in order to evaluate the degree of contamination by this parasite as well as the potential risk incurred on consumption of their meat.

Comparison of excretory/secretory and circulating antigens of Toxoplasma gondii by enzyme immunoassay and immunoblotting.

Toxoplasma gondii trophozoites (RH strain) were cultured in embryonic fibroblasts in order to study the kinetics of production of excretory/secretory antigens, and the results were compared to the production of circulating antigens in an in vivo mouse model. By capture-ELISA, excretory/secretory antigens were first detected on the fourth day of culture whereas circulating antigens were first detected 1 day after infection. Similar concentrations of antigens were detected in both models as evidenced by comparable absorbance values. By immunoblotting, the excretory/secretory antigens were also detected later compared to circulating antigens (day 4 vs day 1). Seven major polypeptides were detected in both antigen preparations, six of them having the same molecular mass (110, 75, 48, 30, 24 and 22 kDa).

Detection of circulating antigens of Toxoplasma gondii in human infection.

Seventy-nine serum specimens from pregnant women and 29 from immunocompromised patients (12 from graft recipients and 17 from patients with acquired immunodeficiency syndrome) were classified into three groups according to their serologic status to Toxoplasma gondii as determined by immunofluorescence and an enzyme-linked immunosorbent assay (ELISA): no antibodies (group 1), acute acquired infection (group 2), and reactivation (group 3). These samples were tested for the presence of circulating antigens (CAg) of T. gondii by capture ELISA and immunoblotting. The presence of CAg was detected by at least one of the two techniques in six of 31 subjects in group 1, 51 of 68 subjects in group 2, and seven of nine subjects in group 3. Of a total of 108 serum specimens, 28 were found to be T. gondii-positive by capture ELISA, 57 by immunoblotting, and 21 by both techniques. Among the nine polypeptides detected by immunoblotting, 38 recognized p14, 17 recognized p8, and 16 recognized p8, and 16 recognized p30. These results demonstrate that the detection of CAg can aid in the diagnosis of infection by T. gondii in humans, especially in immunocompromised patients whose serologic response can be impaired.

Immunoblotting patterns with Mycoplasma pneumoniae of serum specimens from infected and non-infected subjects.

Two hundred and ninety-four serum specimens from 248 subjects, whose complement fixation (CF) titres to Mycoplasma pneumoniae were known, were further investigated by IgG immunoblotting. After analysis of M. pneumoniae proteins by SDS-PAGE, nine polypeptides (p) with mol. wts of 180-43 Kda were selected for immunoblotting studies. Antibodies to M. pneumoniae measured by immunoblotting appeared progressively with age; most subjects more than 19 years old gave positive results. For most of the polypeptides, there was an increase in the frequency of band detection when the CF titres were higher. Furthermore, paired serum specimens from 10 patients with M. pneumoniae infection, as demonstrated by a rise in CF antibody titre, were tested for IgG blotting patterns. Generally, p180 (the P1 adhesin of M. pneumoniae), p172 and p84 were shown to be the dominant targets of the immune response to this organism and may have diagnostic value.

Comparison of PCR, capture ELISA and immunoblotting for detection of Toxoplasma gondii in infected mice.

PCR was compared with capture ELISA and immunoblotting for the detection of Toxoplasma gondii in sera of acutely infected mice. One hundred animals were inoculated intraperitoneally with 5000 trophozoites of RH strain and five of them were killed every 3 h from 3 h to 21 h post infection (p.i.), and every day from day 1 to day 7 p.i.. No assay detected the parasite from 3 h p.i. to 15 h p.i. PCR was the most sensitive assay and detected the T. gondii from 18 h p.i., whereas the other assays detected it only from day 1.

Experimental model of congenital toxoplasmosis in guinea-pigs: use of quantitative and qualitative PCR for the study of maternofetal transmission.

Maternofetal transmission of Toxoplasma gondii was assessed in pregnant guinea-pigs, with a gestational period of 65 +/- 5 days. A total of 56 female guinea pigs was infected by the intraperitoneal route (RH strain), by the oral or the intraperitoneal route (Prugniaud strain; PRU) or by the oral route (76K strain). Inoculation was performed 90 +/- 18 days or 30 +/- 9 days before the onset of gestation or 20 +/- 6 days or 40 +/- 6 days after. Gestational age was determined by a progesterone assay. Parasite loads (fetal brain and liver) were assessed by nested PCR and real-time PCR quantification on Light Cycler was performed with a SYBR Green I technique. The 76K strain appeared to be the most virulent in the model: the neonatal survival rate was 31%, in contrast to 53% and 68% for the PRU and RH strains, respectively. The percentage of survival of neonates for all strains taken together was lower after inoculation at 40 days' gestation (25%) than at 20 days' gestation (77%). Whatever the strain, maternofetal transmission determination was greater with nested PCR (54% for RH, 84% for PRU and 86% for 76K strains) than with real-time quantitative PCR (31% for RH, 66% for PRU and 76% for 76K strains). However, real-time quantitative PCR showed that neonatal parasite load was greater with the cystogenic strains (76K, PRU) and that high hepatic load (> 10000 parasites/g) was often associated with disease severity (11 of 12 cases). Therefore, this technique may provide an important element in understanding this congenital disease.

Detection of immunoglobulin G, M, and A antibodies to enterovirus structural proteins by immunoblot technique in echovirus type 4-infected patients.

Paired serum specimens from 24 patients with echovirus (EV) type 4 infection by virus isolation were tested by the immunoblot technique for the presence of IgG, IgM, and IgA antibodies to EV4 structural proteins. Single sera from 20 patients without neutralizing enterovirus IgM were used as controls. All the sera from EV4-infected patients had IgG antibodies to VP1 of EV4 but also 13 out of the 20 controls. 23 out of 24 EV4-infected patients elicited IgM and IgA specific antibodies to VP1, a pattern highly significant as compared with controls (3/20 for IgM and 8/20 for IgA). In 16 out of the 24 EV4-infected patients, the IgM antibodies were also directed against VP2 (versus 2 out of 20 in the control group). Anti-VP2 IgA were detected in 4 out of the 24 EV4 patients (versus 0 in controls). The 24 paired sera from EV4-infected subjects were also tested by immunoblot technique against three other enteroviruses: EV21, coxsackievirus A9 and poliovirus 1. Cross-reactivities were observed to a large extent against VP1 and VP2 proteins with the three classes of antibodies. These results confirm the data of previous studies on the reactivity of IgM antibodies to various structural proteins that IgG antibodies react exclusively to VP1. Furthermore, this study demonstrates the occurrence of circulating IgA antibodies directed to VP1 and sometimes VP2 in the course of enterovirus infection. The potential interest of this latter finding for diagnosis requires further investigation.

Influence of the quantity of nonspecific DNA and repeated freezing and thawing of samples on the quantification of DNA by the Light Cycler.

Quantification of DNA in real-time using the Light Cycler is increasingly being used for the detection and follow-up of various infectious and other diseases. We evaluated the effect of two parameters, namely the presence of nonspecific DNA and prior repeated freezing and thawing on the accurate quantification of DNA extracts from the RH strain of Toxoplasma gondii by the SYBR Green I and the Hybridization Probe techniques. For both parameters, a high copy number sample containing 5x10(5) parasites/extract and a low copy number sample containing 100 parasites/extract were tested. Reliable quantification was possible in the presence of up to 200 ng of nonspecific DNA by the SYBR Green I technique and up to 1000 ng by the Hybridization Probe technique as compared to the company threshold of 50 and 500 ng, respectively. As tissue samples usually contain more than 200 ng of nonspecific DNA, the ideal choice is the Hybridization Probe technique. The stability of DNA extracts after repeated freeze-thaw cycles was found to be dependent on the volume in which they were stored. Samples stored in 100-microl total volumes were not stable after 3 freeze-thaw cycles, whereas those stored in 1-ml total volumes were stable after 14 freeze-thaw cycles.

Identification and initial characterization of Pneumocystis carinii soluble antigens in rabbit serum and lung lavage.

Lung lavage and serum samples from Azathioprin-treated (acute-phase infection) and untreated (non acute-phase infection) rabbits were used in the immunoblotting technique to look for Pneumocystis carinii (Pc) soluble antigens, using rabbit polyclonal antibodies raised against rabbit-derived Pc antigens and labeled with peroxidase. Analysis of the supernatant of lavage fluid after centrifugation to sediment intact organisms revealed components of approximately 80, 60-65, 55, 39 and 27 kDa in acute-phase samples. The components in the regions of 80, 60-65, 55 kDa and to a lesser extent 39 kDa were also present in non acute-phase lung lavage samples. In acute-phase serum samples, a major component of 80 kDa and minor components of about 65 and 39 kDa are detectable. The 80 and 65 kDa components are also detectable in some of the serum samples from the untreated rabbits. Immunofluorescent staining with FITC-conjugated affinity-purified antibodies to the 80, 60-65, 55, 39 or 27 kDa-components showed that they shared epitopes with both Pc cysts and trophozoites. The affinity-purified antibodies also cross-reacted in immunoblotting with several antigens in the Pc whole preparations. The putative Pc soluble antigens in serum and lung lavage were then isolated by affinity chromatography with polyclonal antibodies to Pc. Preliminary characterization of the column-extracted antigens revealed complete inactivation by trypsin whereas only the 55 and 80 kDa antigens bind to Concanavalin A. In conclusion, the results of this study suggest that Pc soluble antigens are present even in non acute-phase samples and only the low-molecular weight antigens (39 and 27 kDa) seem specific for the acute-phase. These findings are consistent with previous investigations reported by others that development of Pc could occur in nonimmu-nosuppressed rabbits.

Analysis of Pneumocystis carinii antigens by CIEP, SDS-PAGE and immunoblotting.

Pneumocystis carinii (Pc) from rabbit and rat lungs were analyzed by counterimmunoelectro-phoresis (CIEP), Polyacrylamide gel electrophoresis and immunoblotting. In CIEP, considerable cross-reactivity was demonstrated using rabbit polyclonal antisera raised against the rabbit and the rat-derived Pc components. In immunoblotting, both the rat and the rabbit Pc antigens also showed reactivity with the two antisera. Rabbit-derived Pc antigens of about 24-27,39,42-45, 55, 110 and 116 kDa were revealed with infection-derived rabbit sera. The 39, 42-45 and 116 kDa antigens were further recognized by both human and rat immune sera. In addition, many human sera detected the rabbit Pc antigen of 42-45 kDa. Using rat infection-derived sera, rat Pc antigens of 39, 55 to 60, 110 and 116 kDa were identified. The sera from Pc infected rabbits and humans recognized the bands in the regions of 39, 55 and 116 kDa. Carbohydrate residues were further analyzed by Concanavalin A (Con A)-binding experiments, periodate Schiff (PAS) and Alcian Blue (AB) stainings. The 55 and 116 kDa bands of both rabbit and rat Pc strongly reacted with Con A and were stained by PAS indicating the presence of hydroxyl and mannosyl/glycosyl residues. The AB staining-bands were 39, 42-45 and 55 kDa for rabbit Pc isolates and 39, 45, 55-60 and 70 kDa for rat Pc isolates, indicating the presence of carbohydrate residues with acidic function. The rabbit Pc immunodominant 39, 55 and 116 kDa antigens then appeared to be glycoproteins with characteristics similar to those of their counterparts in rats. The implications of these findings are discussed.

Kinetic of circulating antigens by capture ELISA and immunoblotting in murine toxoplasmosis.

Capture ELISA and immunoblotting techniques were applied for the detection of Toxoplasma gondii (T.g) circulating antigens (CAG) in serum specimens of OF-1 mice infected with virulent RH, or cystogenic PGD strains. The capture ELISA assay allowed to detect CAG from the first day of infection to the death of animals with the two T.g strains, although CAG rates were higher when the RH strain was used. Immunoblotting confirmed these findings. Moreover, immunoblotting allowed to identify 7 CAG (MW: 22 kDa to 110 kDa) in serum specimens of mice infected with the RH strain and only 3 (MW: 75 kDa to 110 kDa) in serum specimens of mice infected with the PGD strain. These results are discussed in the light of the evolutive ways of experimental infection by T.g.

Toxoplasma gondii antigens: Analysis by SDS-PAGE and immunoblotting; Relation with circulating antigens.

Cytoplasmic antigenic extracts (CAE) and membranar antigenic extracts (MAE) from Toxoplasma gondii (T.g) purified trophozoites RH strain, were obtained after hypotonic lysis and sonication. Analysis in Polyacrylamide gel electrophoresis (SDS-PAGE) using Coomassie blue staining revealed 21 polypeptides (PP) in CAE and 8 in MAE, whereas the immunoblotting technique detected 28 PP in CAE and 23 in MAE. Immunoblotting is then more sensitive than Coomassie blue staining. This finding is particularly marked for MAE and could be explained by the high antigenicity of some PP that have a lower concentration than the threshold sensitivity of SDS-PAGE. In contrast, some PP in sufficient amount to be detected by SDS-PAGE did not show any antigenic activity since not found by immunoblotting. The molecular weight (MW) ranged from 8 to 130 kDa for cytoplasmic PP and from 4 to 110 kDa for membranar PP. Circulating antigens (CAG) from serum specimens of mice infected with the same strain of T.g were analysed by immunoblotting in comparison with CAE and MAE profiles. From the 7 bands obtained with CAG, 4 were shown to correspond to CAE PP, 2 to common CAE and MAE PP and only 1 to MAE PP (MW: 30 kDa).

Detection of Toxoplasma gondii by polymerase chain reaction in sera of acutely infected mice.

The presence of Toxoplasma gondii DNA was detected in sera of acutely infected mice by polymerase chain reaction. Adult mice were inoculated intraperitoneally with 5 x 10(3) T. gondii RH strain tachyzoites. Five mice were killed every 3 hr from 3 to 21 hr post infection (PI) and every day from 1 to 7 days PI. Toxoplasma gondii DNA was first detected in 60% of the infected mice 18 hr PI and in 100% of the animals 21 hr PI and from 1 to 7 days PI. No mice survived longer than 7 days.

Parasite load in guinea pig foetus with real time PCR after maternofoetal transmission of Toxoplasma gondii.

Parasite loads of different tissues were assessed in guinea pig foetus after maternal infection. Twelve female guinea pigs were infected with 100 cysts of the 76 K strain of Toxoplasma gondii by the oral route. Inoculation was performed 20 +/- 5 days (G20) or 40 +/- 5 days (G40) after the beginning of gestation. Gestational age was determined by progesterone assay. Maternal and foetal organ samples were taken 60 days after the beginning of gestation. Parasite loads (from placenta, amniotic fluid (AF), cord blood (CB), foetal brain, liver, lung and spleen) were assessed by a real-time PCR quantification using fluorescence resonance energy transfer (FRET) hybridization probes on the Light Cycler. Congenital transmission was proven by the presence of parasites in blood or tissue samples of the foetus in 84.6% (11/13) and 100% (16/16) of cases after inoculation on G20 and G40, respectively. The quantitative analysis of our results after inoculation at G20 and G40 has allowed us to determinate the positive parasitic loads as a function of the origin of the sample and the period of inoculation. The parasite loads expressed as log (parasite/g) were low in AF and CB samples: 1.49 +/- 0.50 and 1.05 +/- 0.10 at G20 and 1.21 +/- 0.36 and 1.20 +/- 0.42 at G40 respectively. In contrast the placenta and the different foetal tissues had higher parasite burdens: 2.89 +/- 0.54 to 5.30 +/- 0.51 at G20 and 2.81 +/- 0.71 to 3.65 +/- 0.59 at G40. All the placentae were positive for parasites even in the two cases with no proven transmission. Real time quantitative PCR using the hybridization probe was a very sensitive and reproducible technique to study the kinetics of congenital toxoplasmosis in the guinea pig model wich is close to that of humans.

Evaluation of five commercial tests: complement fixation, microparticle agglutination, indirect immunofluorescence, enzyme-linked immunosorbent assay and latex agglutination, in comparison to immunoblotting for Mycoplasma pneumoniae serology.

A panel of 68 serum specimens from 41 subjects exhibiting various immunological patterns to Mycoplasma pneumoniae as determined by detection of a 180 kDa protein in immunoblotting was used to compare five commercially available tests based on different methods: complement fixation test (CFT), microparticle agglutination (MAG), indirect immunofluorescence assay (IFA), enzyme-linked immunosorbent assay (Elisa), and latex agglutination (LA). The tests were performed according to the manufacturers' instructions. For the determination of immunity to M pneumoniae, the five tests were in good accordance with immunoblotting: sensitivity was 100% for all the five assays, specificity ranged from 95.6% (MAG) to 82.6% (Elisa) and overall agreement ranged from 98.2% (MAG) to 92.8% (Elisa). The comparisons of antibody rates obtained by the four quantitative tests (CFT, MAG, IFA, Elisa) showed correlation coefficients ranging from 0.87 (CFT-IFA) to 0.67 (CFT-Elisa). Six significant antibody rises demonstrated by immunoblotting patterns were detected by all the tests but Elisa in one case. As a whole, the commercial assays gave satisfactory results for routine determination of immune status to M pneumoniae: CFT was the cheapest test and MAG and LA were the easiest to perform.