Estimating the size of the monkeypox virus outbreak in Nigeria and implications for global control.

BACKGROUND: A multi-country outbreak caused by monkeypox virus (MPXV) has been unfolding across endemic and non-endemic countries since May 2022. Throughout April and May 2022, Nigeria reported 31 MPXV cases, of which 11 were confirmed via testing. In May 2022, three internationally exported cases of MPXV, presumed to have originated in Nigeria, were reported, suggesting that a larger than reported outbreak might be occurring in the country. METHODS: We used previously established methods to estimate the true size of the MPXV outbreak in Nigeria. We estimated the incidence rate of exported MPXV cases among all outbound international air travellers from Nigeria during the time period of April and May 2022, using forecasted air traveller volumes. We then applied this incidence rate to the entire population of Nigeria during April and May 2022 assuming that the rate of infection was the same in Nigeria for both travellers and the resident population. Information on the subset of population that were considered to be travellers was obtained from the United Nations World Tourism Organization (UNWTO). RESULTS: We estimated that there were approximately 4000 (N = 4013; 95% CI: 828-11 728) active cases of MPXV in Nigeria in April and May 2022. This is approximately 360-fold greater than the confirmed number and approximately 130-fold greater than the reported number of cases in Nigeria. CONCLUSION: Our findings suggest that a larger outbreak than is appreciated may be ongoing in Nigeria. The observed international spread of MPXV offers important insights into the scale of the epidemic at its origin, where clinical detection and disease surveillance may be limited. These findings highlight the need to expand and support clinical, laboratory, and public health capacity to enable earlier detection of epidemics of international significance.

Improved inference of time-varying reproduction numbers during infectious disease outbreaks.

Accurate estimation of the parameters characterising infectious disease transmission is vital for optimising control interventions during epidemics. A valuable metric for assessing the current threat posed by an outbreak is the time-dependent reproduction number, i.e. the expected number of secondary cases caused by each infected individual. This quantity can be estimated using data on the numbers of observed new cases at successive times during an epidemic and the distribution of the serial interval (the time between symptomatic cases in a transmission chain). Some methods for estimating the reproduction number rely on pre-existing estimates of the serial interval distribution and assume that the entire outbreak is driven by local transmission. Here we show that accurate inference of current transmissibility, and the uncertainty associated with this estimate, requires: (i) up-to-date observations of the serial interval to be included, and; (ii) cases arising from local transmission to be distinguished from those imported from elsewhere. We demonstrate how pathogen transmissibility can be inferred appropriately using datasets from outbreaks of H1N1 influenza, Ebola virus disease and Middle-East Respiratory Syndrome. We present a tool for estimating the reproduction number in real-time during infectious disease outbreaks accurately, which is available as an R software package (EpiEstim 2.2). It is also accessible as an interactive, user-friendly online interface (EpiEstim App), permitting its use by non-specialists. Our tool is easy to apply for assessing the transmission potential, and hence informing control, during future outbreaks of a wide range of invading pathogens.

Novel peptidomimetic hematoregulatory compounds.

The activity of a novel series of peptidomimetic hematoregulatory compounds, designed based on a pharmacophore model inferred from the structure activity relationships of a peptide SK&F 107647 (1), is reported. These compounds induce a hematopoietic synergistic factor (HSF) which in turn modulates host defense. The compounds may represent novel therapeutic agents in the area of hematoregulation.

Identification of unique truncated KC/GRO beta chemokines with potent hematopoietic and anti-infective activities.

SK&F 107647, a previously described synthetic immunomodulatory peptide, indirectly stimulates bone marrow progenitor cells and phagocytic cells, and enhances host defense effector mechanisms in bacterial and fungal infection models in vivo. In vitro, SK&F 107647 induces the production of a soluble mediator that augments colony forming cell (CFU-GM) formation in the presence of CSFs. In this paper we purified and sequenced the stromal cell-derived hematopoietic synergistic factors (HSF) secreted from both murine and human cell lines stimulated with SK&F 107647. Murine HSF is an N-terminal 4-aa truncated form of the CXC chemokine, KC, while human HSF was identified as an N-terminal 4-aa truncated form of the CXC chemokine, GRO beta. In comparison to their full-length forms, truncated KC and truncated GRO beta were 10 million times more potent as synergistic growth stimulants for CFU-GM. Enhanced potency of these novel truncated chemokines relative to their full-length forms was also demonstrated in respiratory burst assays, CD11b Ag expression, and intracellular killing of the opportunistic pathogen, Candida albicans. Administration of truncated KC significantly enhanced survival of mice lethally infected with C. albicans. The results reported herein delineate the biological mechanism of action of SK&F 107647, which functions via the induction of unique specific truncated forms of the chemokines KC and GRO beta. To our knowledge, this represents the first example where any form of KC or GRO beta were purified from marrow stromal cells. Additionally, this is the first demonstration of in vivo efficacy of a CXC chemokine in an animal infectious fungal disease model.

Isolation and characterization of a sigB deletion mutant of Staphylococcus aureus.

The sigB gene of Staphylococcus aureus, coding for the alternate sigma factor B, has been deleted by allelic replacement mutagenesis. The mutant grew as well as the parent in vitro, although it was deficient in clumping factor, coagulase, and pigment. In two murine and one rat infection model the mutant showed no reduction in virulence.

Effects of SKF 108922, an HIV-1 protease inhibitor, on retrovirus replication in mice.

Rationally designed synthetic inhibitors of retroviral proteases inhibit the processing of viral polypeptides in cultures of human T lymphocytes infected with human immunodeficiency virus type 1 (HIV-1) and therefore suppress the infectivity of HIV-1 in vitro. We have previously reported the antiviral activity in vitro of HIV-1 protease inhibitors against the C-type retrovirus Rauscher murine leukemia virus (RMuLV) and the lentivirus simian immunodeficiency virus (SIV). The same compounds which blocked the infectivity of HIV-1 also inhibited the infectivity of RMuLV and SIV in vitro. This report extends these findings by testing the antiviral activity of HIV-1 protease inhibitors in vivo in the RMuLV model. RMuLV-infected mice were treated twice a day (bid) with either an active (SKF 108922) or inactive (SKF 109273) compound for fourteen days by the intraperitoneal (i.p.) route. Compared with excipient control, SKF 108922, formulated with hydroxypropyl-beta-cyclodextrin (HPB), reduced virus-induced splenomegaly, viremia, and serum reverse transcriptase (RT) levels, while SKF 109273 was inactive. The HPB vehicle by itself enhanced replication of RMuLV. The effects of changing the formulation and the route of administration were examined. SKF 108922, formulated in HPB, had similar antiviral activity when administered by the i.p. or subcutaneous (SC) routes. However, SKF 108922 administered as a colloidal suspension in cholesterol sulfate (CS) had no detectable antiviral effect. Measurements of the circulating levels of the protease inhibitor in plasma explained this result. Plasma concentrations of SKF 108922 exceeded 1000 nM within 10 min after SC administration of the compound solubilized in HPB, but SKF 108922 was not detected in plasma after SC administration of the same dose formulated with CS. Information on optimal conditions for administering these agents should prove useful in guiding their clinical application Therefore, RMuLV should provide a good model for the preclinical evaluation and development of this class of agents for the treatment of HIV.

Treatment of experimental gram-negative and gram-positive bacterial sepsis with the hematoregulatory peptide SK&F 107647.

SK&F 107647, a novel synthetic low-molecular-weight peptide, has demonstrated potent antiinfective activities in murine models of fungal and viral infection. To determine if the hematoregulatory activities of SK&F 107647 could offer protection over conventional antibiotic therapy or as a single agent in animal models of bacterial sepsis, rats were implanted intraperitoneally with a live bacteria-containing fibrin-thrombin clot. Rats pretreated subcutaneously or orally with SK&F 107647 and then infected with either a gram-negative (Escherichia coli) or a gram-positive (Staphylococcus aureus) bacteria-containing clot demonstrated significantly improved survival over control formulation-treated animals. Treated animals showed increased effector cell activation, measured by CD11b expression on neutrophils and monocytes, and up to 1000-fold reduction in the number of E. coli recovered from blood. Thus, the hematoregulatory activities of SK&F 107647 can increase natural host resistance to infections caused by both gram-negative and gram-positive bacteria.

An orally bioavailable HIV-1 protease inhibitor containing an imidazole-derived peptide bond replacement: crystallographic and pharmacokinetic analysis.

(2R,4S,5S,1'S)-2-Phenylmethyl-4-hydroxy-5-(tert-butoxycarbonyl) amino-6-phenylhexanoyl-N-(1'-imidazo-2-yl)-2'-methylpropanamide (compound 2) is a tripeptide analogue inhibitor of HIV-1 protease in which a C-terminal imidazole substituent constitutes an isoelectronic, structural mimic of a carboxamide group. Compound 2 is a potent inhibitor of the protease (K(i) = 18 nM) and inhibits HIV-1 acute infectivity of CD4+ T-lymphocytes (IC50 = 570 nM). Crystallographic analysis of an HIV-1 protease-compound 2 complex demonstrates that the nitrogen atoms of the imidazole ring assume the same hydrogen-bonding interactions with the protease as amide linkages in other peptide analogue inhibitors. The sole substitution of the C-terminal carboxamide of a hydroxyethylene-containing tripeptide analogue with an imidazole group imparts greatly improved pharmacokinetic and oral bioavailability properties on the compound compared to its carboxamide-containing homologue (compound 1). While the oral bioavailability of compound 1 in rats was negligible, compound 2 displayed oral bioavailabilities of 30% and 14%, respectively, in rats and monkeys.

Efficacy of the hematoregulatory peptide SK&F 107647 in experimental systemic Candida albicans infections in normal and immunosuppressed mice.

SK&F 107647, a novel synthetic dimeric pentapeptide, has been shown to be a potent hematoregulatory agent. The potential for the hematoregulatory factors elicited by SK&F 107647 to confer protection in experimental models of systemic Candida albicans infection was evaluated in immunosuppressed and immunocompetent mice. Prophylactic treatment with recombinant human interleukin-1 (rhIL-1), recombinant human granulocyte colony stimulating factor (rhG-CSF), or the hematoregulatory peptide SK&F 107647 significantly increased survival times in gamma irradiated immunosuppressed as well as non-irradiated immunocompetent mice challenged with a lethal dose of C. albicans. Protection was also observed in athymic nu/nu "nude" mice. Additionally, significant increases in survival in non-irradiated immunocompetent mice dosed by oral gavage were observed. These results indicate that SK&F 107647 can significantly enhance natural host resistance to experimental C. albicans infections both in immunosuppressed and immunocompetent mice.

In vivo modulation of hematopoiesis by a novel hematoregulatory peptide.

The hematoregulatory peptide dimer, HP5B, enhances myelopoiesis by stimulating stromal cell cytokine production. However, the disulfide bridge of this peptide is susceptible to reduction, leading to the formation of monomeric pentapeptide, HP5, a direct-acting inhibitor of myelopoiesis. We have replaced the disulfide (S-S) bond of HP5B dimer with an isosteric ethylene (CH2-CH2) group, creating a new, nonreducible, metabolically more stable peptide (SK&F 107647). This novel peptide was tested in vitro and in vivo for hematopoietic effects. In vitro, SK&F 107647 has no direct colony-stimulating activity (CSA). Stimulation of murine stromal cells with SK&F 107647 results in production and release of CSA at concentrations as low as 0.01 ng/mL, at least 10-fold lower than observed with HP5B dimer. Injection of SK&F 107647 in normal mice results in a two- to six-fold increase in serum CSA, which becomes maximal at 6 hours postinjection. Administration of peptide daily over 4 days (q.d. x 4) by both parenteral and oral routes results in significant increases in absolute numbers of granulocyte-macrophage (CFU-GM), erythroid (BFU-E), and multipotential (CFU-GEMM) progenitor cells, as well as stimulating their cell cycle rates. A doubling in day 8 CFU-S was also observed in SK&F 107647-treated mice. Continuous subcutaneous (s.c.) infusion of SK&F 107647 in femorally cannulated rats demonstrated modest but significant elevation of peripheral blood neutrophil and monocyte counts within 7 days. SK&F 107647 represents a novel synthetic hematoregulatory peptide that shares biological and/or modulatory activities with natural hematopoietic cytokines.

Divergent patterns of pulmonary blastomycosis induced by conidia and yeasts in athymic and euthymic mice.

Athymic nude (nu/nu) mice are uniformly more susceptible than euthymic nu/+ mice to lethal infection with intranasally inoculated Blastomyces dermatitidis, whether infection is initiated by yeasts or conidia. Conidial infection requires a high inoculum size; the disease produced is prolonged and disseminated. Yeasts are infective at a low inoculum size and produce a rapidly fatal pneumonia. Thymus transplantation is more protective for conidia-infected than yeast-infected nude mice, presumably because the disease course is long enough for an effect to become demonstrable. Yeast inocula multiply more rapidly in the lungs than do conidial inocula. This may relate to the greater susceptibility of conidia to heterophils evoked in the airways, and the fact that yeasts derived from conidial inocula must survive in the face of an established inflammatory reaction. When yeasts and conidia are inoculated simultaneously, the disease produced is less severe than when yeasts are inoculated alone, presumably because of a more intense and diffuse inflammatory response engendered by the conidia. Suppression of conidia-derived yeast replication is demonstrable for at least 1 wk in nu/nu mice and for 2 to 3 wk in nu/+ mice. The latter delay appears attributable to the intact immune system in nu/+ mice, and the probability that cellular immunity limits the subsequent replication of yeasts. Eventually, the immune response fails to control yeast replication, and the mice succumb. These studies provide further insights into the role of the thymus in host defense against B. dermatitidis and the basis for the differential pace of infection when mice are infected with yeasts or conidia.

A Legionella-specific DNA probe detects organisms in lung tissue homogenates from intranasally inoculated mice.

We have prepared a DNA probe from internal sequences of the gene encoding the Legionella pneumophila major outer membrane protein (MOMP). Immunologic studies of the MOMP have confirmed that it possesses both genus-specific and species-specific antigenic domains, but possesses no cross-reactivity with non-Legionella species. At the DNA levels, the 3' half of the gene contains sequences that are homologous to DNA from all strains tested within the genus, whereas the 5' half of the gene has homology with L. pneumophila strains only. Homology of the gene with non-legionellae has not been detected even under low stringency conditions. To test the utility of this probe for detecting organisms in tissue, we tested crude homogenates of mouse lungs representing 1/1,000th of the total lung mass. After intranasal inoculation with 2 X 10(8) colony-forming units of L. pneumophila, mice were sacrificed at various intervals (10 mice per group). Since L. pneumophila does not produce a propagating infection in these animals, cultures of lung tissue from successive days after inoculation showed a roughly linear decline in viable L. pneumophila (total lung yield: 10(8) on Day 0, 5 X 10(7) on Day 2, 10(5) on Day 5, 10(3) on Day 9, and less than 10(2) on Day 15). By DNA dot hybridization with the MOMP probe, we detected positive signals from most animals on Days 0 and 2, suggesting a threshold sensitivity of between 50,000 and 100,000 organisms with our current methods. Advances in DNA probe technology may soon permit the rapid, specific identification of either L. pneumophila or other Legionella species in pathologic specimens.

The critical role of CO2 in the morphogenesis of Coccidioides immitis in cell-free subcutaneous chambers.

In order to ascertain the factors controlling conversion of Coccidioides immitis arthroconidia to endosporulating spherules, studies were conducted with the use of subcutaneously implanted dialysis chambers in mice. The dialysate had the following characteristics: pH approximately 7.36; CO2 partial pressure, approximately 50 mm Hg; O2 partial pressure, approximately 140 mm Hg; protein content, approximately 20 mg/ml; and no cells. When chambers were inoculated with arthroconidia, endosporulating spherules developed. Introduction of syngeneic phagocytes had no effect. When dialysate or autologous serum was studied in vitro in room air, arthroconidia converted to mycelia unless CO2 supplementation (CO2 partial pressure, 20-80 mm Hg) was provided, in which case endosporulating spherules developed. The effect of CO2 could not be reproduced with either NaHCO3 or other buffers. These studies indicate that CO2 at a partial pressure found in normal host tissues is essential for formation of endosporulating spherules and that host phagocytes are not needed for such conversion in tissue fluids, either in vivo or in vitro.