Risk assessment of recent Egyptian H5N1 influenza viruses.

Highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype are enzootic in poultry populations in different parts of the world, and have caused numerous human infections in recent years, particularly in Egypt. However, no sustained human-to-human transmission of these viruses has yet been reported. We tested nine naturally occurring Egyptian H5N1 viruses (isolated in 2014-2015) in ferrets and found that three of them transmitted via respiratory droplets, causing a fatal infection in one of the exposed animals. All isolates were sensitive to neuraminidase inhibitors. However, these viruses were not transmitted via respiratory droplets in three additional transmission experiments in ferrets. Currently, we do not know if the efficiency of transmission is very low or if subtle differences in experimental parameters contributed to these inconsistent results. Nonetheless, our findings heighten concern regarding the pandemic potential of recent Egyptian H5N1 influenza viruses.

Classification of clinical falciparum malaria and its use for the evaluation of chemosuppression in children under six years of age in Liberia, west Africa.

The possible role of malaria as cause of morbidity was assessed during one year in 262 children aged 6 months to 6 years living in two villages in a rural area of Liberia. The study population was followed by weekly clinics and three-monthly surveys and the children were randomly allocated to receive either chloroquine or placebo every 3 weeks. The morbidity of the children was evaluated by criteria based on the history and the clinical condition into four different stages, in order to describe the probability that an observed clinical event could be attributed to malaria infection, based on the presence of detectable parasites in the blood, the history the previous week, and the clinical status of the child. The level of anaemia, splenomegaly and measured body temperature supported that malaria was the major contributor to the overall morbidity observed. Based on the stage classification of clinical illness, children were classified as having 'possible clinical malaria' or 'probable clinical malaria'. Malaria appeared to be an important cause of febrile episodes during both dry and rainy seasons. During the rainy season more than 60% of the children experienced at least one clinical malaria episode, and during the dry season more than 50% of the children experienced at least one clinical attack of malaria. Children receiving chemosuppression had overall fewer clinical malaria attacks, and the effect of the chemosuppression was most pronounced in the dry season, the odds ratio comparing children receiving regular chemosuppression with children receiving presumptive treatment only was estimated to 0.39 (0.25-0.62).

Human infection by genetically diverse SIVSM-related HIV-2 in west Africa.

Our understanding of the biology and origins of human immunodeficiency virus type 2 (HIV-2) derives from studies of cultured isolates from urban populations experiencing epidemic infection and disease. To test the hypothesis that such isolates might represent only a subset of a larger, genetically more diverse group of viruses, we used nested polymerase chain reactions to characterize HIV-2 sequences in uncultured mononuclear blood cells of two healthy Liberian agricultural workers, from whom virus isolation was repeatedly unsuccessful, and from a culture-positive symptomatic urban dweller. Analysis of pol, env and long terminal repeat regions revealed the presence of three highly divergent HIV-2 strains, one of which (from one of the healthy subjects) was significantly more closely related to simian immunodeficiency viruses infecting sooty mangabeys and rhesus macaques (SIVSM/SIVMAC) than to any virus of human derivation. This subject also harboured multiply defective viral genotypes that resulted from hypermutation of G to A bases. Our results indicate that HIV-2, SIVSM and SIVMAC comprise a single, highly diverse group of lentiviruses which cannot be separated into distinct phylogenetic lineages according to species of origin.

The antibody response to well-defined malaria antigens after acute malaria in individuals living under continuous malaria transmission.

The IgG and IgM antibody responses to the C-terminal 783 amino acids of the P. falciparum glutamate-rich protein, GLURP489-1271, expressed as an E. coli fusion protein, the IgG response to a 18-mer synthetic peptide EDKNEKGQHEIVEVEEIL (GLURP899-916) representing the C-terminal repeats of GLURP, and a synthetic peptide (EENV)6 representing the C-terminal repeats from Pf155/RESA, were investigated longitudinally in 13 children and 7 adults living under conditions of continuous, intense malaria transmission. Some subjects did not recognize the antigens after malaria infection, and in subjects recognizing the antigens, the responses were often short-lived. In adults, the antibody responses to the GLURP489-1271 fusion protein and the (EENV)6 peptide peaked after 2 weeks, and not all individuals responded to all antigens. The antibody response, even against large fragments of conserved antigens, is not uniformly elicited by natural malaria infection in previously primed donors.

The effect of splenectomy on immunity to Plasmodium malariae and P. falciparum in a malaria immune donor.

A 55 year old Liberian male was splenectomized after an abdominal trauma. A few days after splenectomy he experienced a pure Plasmodium malariae infection with high fever. He was later followed for 12 months with monthly blood films and temperature measurements, and did never show any signs of clinical malaria. The parasite densities observed during the longitudinal follow after splenectomy did not differ from parasite densities in villagers with intact spleens.

Clinical and parasitological studies on malaria in Liberian adults living under intense malaria transmission.

Occurrence of fevers and chills, headaches and body and joint pains, and body temperature and malaria parasitaemias were recorded monthly for a year for 121 Liberian adults. There was no apparent correlation between any of the symptoms and the presence or density of blood parasites; it was therefore not possible to define a case of clinical malaria in the study population, which was probably highly immune to infection. Only a few people with patent blood infections had elevated blood temperatures and these were below 37.5 degrees C. Malaria prevalence and levels of parasitaemia declined with age and indicated that immunity continues to develop well into adult age. The data did not support the view that adults experience symptoms at lower parasitaemias than children. Pregnant and non-pregnant women had similar levels of symptoms, but high levels of parasitaemia were found more frequently in the pregnant group.

Development of immunity against Plasmodium falciparum malaria: clinical and parasitologic immunity cannot be separated.

A total of 1622 individuals of all ages living under conditions of continuous malarial transmission in Liberia were enrolled in a cross-sectional study of parasite rates, positive parasite densities, and body temperatures. The age-specific Plasmodium falciparum-positive parasite densities were greatest at ages 0.5-1.0 year, then slowly declined into adulthood. The age-specific mean body temperature at parasite isodensity showed a steady decline even in the oldest age group. The results do not support the hypothesis that adults have higher body temperatures at a given parasite density than do children with the same parasite density. The age-specific P. falciparum parasite density for specific isotemperatures showed that a subgroup of children in the age group 0.5-1.0 year had low temperatures (less than 36.5 degrees C) despite high parasite densities. This indicates that low body temperature should be investigated further as a possible indicator of serious malaria in young children. Parasitologic and clinical immunity develops concomitantly and cannot be separated. The findings do not support the hypothesis that a special "anti-disease" immunity exists independently of parasitologic immunity.

Plasma, erythrocyte and urine concentrations of chlorproguanil and two metabolites in man after different doses.

Failures in the prophylactic effect of the antimalarial biguanide chlorproguanil (Lapudrine) may be caused by insufficient levels of its active metabolite chlorcycloguanil. Concentrations of chlorproguanil, chlorcycloguanil and a second metabolite, dichlorophenylbiguanide, in plasma, erythrocytes and urine, were followed in 13 volunteers, using a HPLC assay. In an initial study the basic kinetics were investigated after an oral dose of 2 mg kg-1. In the main study, the concentration-time curves were followed for 1 week after an oral dose of 20 or 80 mg chlorproguanil, respectively, after either a single dose or one weekly dose for 5 weeks. Higher concentrations of all three compounds were found in erythrocytes than in plasma. The active substance, chlorcycloguanil, was below the probably effective concentration in erythrocytes 24 h after 20 mg chlorproguanil and 72 h after 80 mg. The urinary recovery was about 45% of the dose and t1/2 31-44 h, both higher than previously reported. The apparent clearance was 0.52-0.82 l h-1 kg-1, which is lower than previously found. It is suggested that improved dose regimens, e.g. a higher dose given once a week, should be clinically tested on basis of these kinetic results.

Longitudinal study of seroreactivities to Pf155/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.

A longitudinal study of seroreactivities to Plasmodium falciparum antigens in infants and children living in a holoendemic area of Liberia.

Investigators studied 348 children age 0-10 years, living in a holoendemic area of Liberia, for parasitological, serological and clinical parameters. The age-specific parasite rate increased towards the 7-10 year-old age group in which it was 86.8%. The geometrical mean parasite density decreased from the 3-4 year-old age group, in which fewer episodes of clinical malaria were observed. Antibodies to crude Plasmodium falciparum parasite antigens were detected in all children. The (EENV)6 seropositive rate was a maximum of 67.9% in the 3-11 month-old age group. It declined to a minimum of 31.7% in the 5-6 years age group after which it increased slowly in the 7-10 years age group. Antibodies to the synthetic peptide (NANP)6 showed a steady seropositive rate after the age of 3 months, between 30.0% and 39.3% in all the age groups up to 10 years. No statistically significant correlation was found between seropositivity to (EENV)6 and malarial parasitemia. In contrast, a statistically significant positive correlation was found between seropositivity to (NANP)6 and parasite rates. The antibody response for the individual child was transient to both Pf155/RESA, measured by immunofluorescence, and to (EENV)6 and (NANP)6, measured by ELISA, especially in the younger age groups of this study population. Parasitological and clinical immunity developed before a stable antibody response to these defined malaria antigens was established. These antibodies may still contribute to the immune protection against malaria, but they were not reliable parameters for protective immunity in the population we studied.

In vitro and in vivo susceptibility of Plasmodium falciparum isolates from Liberia to pyrimethamine, cycloguanil and chlorcycloguanil.

In vivo susceptibility of Plasmodium falciparum to chlorproguanil and in vitro susceptibility to pyrimethamine, cycloguanil and chlorcycloguanil were studied in 38 children from two Liberian villages. Children in one village (Lagbala) had received monthly chemosuppression with chlorproguanil from 1976-1985, and children in the other village (JDF) had received fortnightly chlorproguanil from 1981-1985. The highest and lowest IC100 for pyrimethamine differed by a factor of 10(5), but they differed only by a factor of 10(3) for chlorcycloguanil. The mean IC100 for chlorcycloguanil was significantly lower (P less than 0.0001) than the mean IC100 for pyrimethamine and cycloguanil, and the IC100 for the samples most resistant to chlorcycloguanil (10(-8) M) was still well below peak blood concentrations after chlorproguanil administration. Resistance could be defined as IC100 greater than or equal to 10(-6) M for pyrimethamine and IC100 greater than or equal to 10(-8) M for chlorcycloguanil. The isolates most resistant or most sensitive to pyrimethamine were also the most resistant or most sensitive to chlorcycloguanil, indicating partial cross-resistance between the two drugs. The in vivo response to chlorproguanil 1.5 mg kg-1 in Lagbala was equal to the response in 1983. Chlorproguanil 1.5 mg kg-1 resulted in lower parasite rates on day 3 and 7, but did not prevent 60% of the children requiring treatment with chloroquine during the four weeks' follow-up after chlorproguanil administration.

Improvement in plasma protein concentrations with fibronectin treatment in severe malnutrition.

Severely malnourished young children (n = 72) were treated with intravenous fibronectin to assess its efficacy as an adjunct treatment for kwashiorkor and/or marasmus. The protein was given in a double-blind study during the first 4 d of hospitalization together with standard nutrition and supportive therapy. Fibronectin concentrations as well as albumin, transferrin, prealbumin, and alpha-2-macroglobulin were monitored in samples taken before each dose of fibronectin and in samples taken five times thereafter. Sick individuals had significantly lower concentrations of all five proteins than did healthy control individuals of matching ages. Mean fibronectin concentrations were 98 +/- 7 mg/L (mean +/- SEM) for sick vs 303 +/- 21 mg/L for healthy individuals. Concentrations of all five proteins increased at a greater daily rate in patients treated with fibronectin than in patients who received placebos. Eighty-seven percent of the treated children survived to the end of the treatment and observation periods (mean hospitalization 14.7 d) whereas only 56% of the control subjects survived (P = 0.004). These data support the use of intravenous fibronectin as an adjunct in the treatment of severe malnutrition at a dosage of 7.5 mg.kg-1.d-1 over a 4-d period.

A longitudinal study of antibodies to the Plasmodium falciparum antigen Pf155/RESA and immunity to malaria infection in adult Liberians.

118 adult Liberians from 2 villages were studied prospectively for one year with monthly blood examinations for malaria parasites. The crude parasite rate was 41.5% and the crude gametocyte rate was 6.1%. The inoculation rate varied between 0.075 in the dry season and almost 0.4 in the rainy season, which is in accordance with other data from holoendemic areas. 47.5% (56) had a titre to the Pf155/RESA antigen less than or equal to 1/50 ('low responders') and 52.5% (62) had a titre of greater than or equal to 1/250 ('high responders'). The response was not age-dependent in this adult population, which may suggest that genetic factors are determining whether the individual become a high or low responder. Antibodies against the Pf155/RESA antigen were measured in 2 surveys 8 months apart, and the mean antibody response to Pf155/RESA and its EENV sequence was constant without seasonal variation. Pf155/RESA high responders had lower parasite densities during all 3 seasons surveyed, and Pf155/RESA high responders, with high antibody reactivity against the (EENV)6 sequence from the 3' repeat region of Pf155/RESA, had significantly lower parasite densities in the rainy season of 1987. The data suggest that high titres of antibodies to the Pf155/RESA antigen, and especially to its EENV sequence, might play a role in protective immunity in adults.

Consecutive determinations of seroreactivities to Pf 155/RESA antigen and to its different repetitive sequences in adult men from a holoendemic area of Liberia.

Sera from 32 adult men residing in a malaria holoendemic area of Liberia were investigated for seroreactivities to different asexual blood-stage malaria antigens on five consecutive occasions from 1984 to 1986. The seroreactivities to crude parasitic antigens and to Pf 155/RESA (EMIF) were determined by immunofluorescence and to repetitive sequences of Pf 155/RESA by enzyme-linked immunosorbent assay (ELISA). All sera were highly reactive against the crude parasitic antigens with reciprocal titres varying from 5000 to 100,000. The EMIF titres showed a wider variation from negative (less than 10) to 25,000, and when the same individuals were re-examined on subsequent surveys similar EMIF titres were found. The ELISA seroreactivities to three different repetitive sequences of Pf 155/RESA also showed different individual profiles which were rather consistent on consecutive surveys. High EMIF titres appeared to be correlated mainly to one of the peptide sequences, namely (EENV)2. The consistent individual profiles of the seroreactivities to Pf 155 and its repetitive sequences suggest genetic restriction of the humoral immune response. Although no significant correlation was found between EMIF titres and parasitic densities in the adult hyperimmune men the specific peptides, however, offer new possibilities of further investigating protective capacities of different immune responses to specific epitopes of the malaria parasite.

An epidemiological study of humoral and cell-mediated immune response to the Plasmodium falciparum antigen PF155/RESA in adult Liberians.

We investigated the seroreactivity and T cell reactivity against the Plasmodium falciparum antigen Pf155/RESA, different oligopeptides from the 3' and 5' repeat regions of the Pf155/RESA antigen, and crude Plasmodium falciparum antigens in 164 adult Liberians. We compared 2 long-term residential groups with high and low exposure to malaria. The seropositive rate to the peptides was significantly higher with increased exposure. There was no significant difference in response rates to the Pf155/RESA. This may indicate the level of persistent T cell memory in previously primed donors. The seropositive rates to 3 Pf155/RESA peptides and the rates measured by either 3H-thymidine incorporation or IFN-gamma release after stimulation with Pf155/RESA and the peptides were all lower in parasite positive individuals. Even low grade, asymptomatic parasitemia can impair the T cell response in vitro. The lower antibody response in parasite positive subjects may be explained by either antibody consumption or lower protection against malaria parasitemia in subjects with low concentrations of antibodies against the Pf155/RESA antigen.

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.

Susceptibility of Plasmodium falciparum to chloroquine in northern Liberia after 20 years of chemosuppression and therapy.

The in vivo and in vitro susceptibility of Plasmodium falciparum to chloroquine was investigated in northern Liberia after 20 years of continuous chemosuppression and therapy with 4-aminoquinolines. In all patients studied (n = 53) parasitaemias were cleared within four days. There were no recrudescences in 16 patients followed-up for 28 days. All isolates of P. falciparum tested in vitro (n = 26) showed sensitive patterns. Schizont maturation was inhibited by a chloroquine concentration of between 0.25 and 0.75 mumol-1. In this area of Liberia no resistance to chloroquine was found in spite of extensive use of 4-aminoquinolines. This may support the view that importation of at least partially resistant strains, rather than local mutation of P. falciparum, precedes selection of resistant strains. Hence, we conclude that regular intake of chloroquine by groups at risk is justified if it is combined with regular monitoring of drug susceptibility.

Malaria control by chlorproguanil. I. Clinical effects and susceptibility of Plasmodium falciparum in vivo after seven years of monthly chlorproguanil administration to children in a Liberian village.

For seven years, chlorproguanil (1.0 to 2.0 mg kg-1) was administered monthly to the children below 15 years of age in a village with holoendemic malaria. Malariometric indices were recorded every six months. Susceptibility in vivo was monitored by the clearance of Plasmodium falciparum parasitaemia after drug intake. Three parasite species were found initially: P. falciparum (52%), P. malariae (8%) and P. ovale (4%). The parasites found during the study were mainly P. falciparum, and parasite rates ranged from 37 to 87% at the different surveys one month after respective drug intake. A fifty-fold decrease of mean parasite density was generally observed seven days after drug intake. Splenomegaly was initially recorded in all two to nine year old children, with a mean size of 2.64 according to Hackett's index. From 18 months onwards as the mean spleen index was 1.15 in the same age group. Chlorproguanil may represent an important alternative drug to groups at risk in malaria control schemes.

Endemic Lassa fever in Liberia. V. Distribution of Lassa virus activity in Liberia: hospital staff surveys.

Serological testing of hospital personnel by the indirect fluorescent antibody (IFA) technique was used to indicate the distribution of Lassa virus (LV) activity in Liberia. Determination of the places of origin of the staff members as well as the sites of the hospitals indicated that LV is active in throughout Liberia. Prevalences of IFA varied from 3.8% at the J. J. Dossen Hospital on the coast in the south-east to 22.3, 23.5 and 40.4% in Lofa County hospitals inland in the north-west. Rises in LV antibody prevalences, high prevalences and relatively high IFA titres in hospital personnel suggest the LV activity is particularly high in Lofa, Grand Cape Mount and Nimba Counties.