Empirical analysis suggests continuous and homogeneous circulation of Newcastle disease virus in a wide range of wild bird species in Africa.

Newcastle disease (ND) is one of the most important poultry diseases worldwide and can lead to annual losses of up to 80% of backyard chickens in Africa. All bird species are considered susceptible to ND virus (NDV) infection but little is known about the role that wild birds play in the epidemiology of the virus. We present a long-term monitoring of 9000 wild birds in four African countries. Overall, 3·06% of the birds were PCR-positive for NDV infection, with prevalence ranging from 0% to 10% depending on the season, the site and the species considered. Our study shows that ND is circulating continuously and homogeneously in a large range of wild bird species. Several genotypes of NDV circulate concurrently in different species and are phylogenetically closely related to strains circulating in local domestic poultry, suggesting that wild birds may play several roles in the epidemiology of different NDV strains in Africa. We recommend that any strategic plan aiming at controlling ND in Africa should take into account the potential role of the local wild bird community in the transmission of the disease.

Impacts on nontarget insects of a new insecticide compound used against the desert locust [Schistocerca gregaria (Forskål 1775)].

In 1994, the effects of fipronil, a new insecticide compound of the phenyl-pyrazol chemical group, was tested against desert locusts during a field experiment in Mauritania. The impacts of these spray treatments on nontarget Coleoptera and Hymenoptera were also studied. In relation to organophosphorous insecticides usually used against grasshoppers and locusts, fipronil appeared more effective and persistent. Similar results were obtained for nontarget Carabidae and Tenebrionidae which were almost totally eliminated from the treated plot. The effects on Hymenoptera varied according the family; Scelionidae and Sphecidae seemed to be more affected than Apoidea. Positive and negative aspects of fipronil treatments are discussed. Appearing as one of the most convenient insecticides to successfully prevent locust outbreaks, at a very early stage of invasion under Saharan conditions, fipronil simultaneously induces heavy mortality in some nontarget insect groups.

A new mechanism for the reabsorption of thyroid iodoproteins: selective fluid pinocytosis.

Rat thyroid hemilobes were incubated in presence of exogeneous, heterologous and homologous thyroglobulins. The median density of the thyroglobulin molecules originally added to the medium was compared with that of the molecules remaining at the end of a three-hour incubation period (37 degrees C). A certain degree of specificity in the reabsorption process of thyroglobulin was found: the uptake of homologous molecules (rat) was higher than heterologous (hog) molecules. The median density of the iodoproteins remaining after the incubation did not change for the heterologous whereas it shifted towards lower density for the homologous thyroglobulins (equilibrium labelled, 35 iodine atoms/molecule). In addition, rat follicular cells display selectivity in the endocytosis of homologous thyroglobulin. Among the rat molecules, the normally iodinated are taken up more actively than the lowly iodinated or newly synthesized ones. Dissimilarity in the median density of the thyroglobulin molecules before and after endocytosis was only evident for the equilibrium-labelled, normally iodinated rat preparation: the disappearance from the medium of 25-30% of exogenous iodoproteins was sufficient to lower significantly the median density of the remaining molecules. This means that the thyroglobulin molecules having higher density are taken up preferentially by the tissue. A mechanism involving specific interactions between the iodoproteins and the surface of thyroid cell is suggested.

Hormonal and nutritional status: critical conditions for endemic goiter epidemiology?

Recent advances in protein metabolism and in glycoprotein synthesis bring further insight into endemic goiter epidemiology. Retinol circulates in the blood stream in close parallelism with retinol-binding protein and prealbumin (RBP-PA), a protein complex whose liver secretory rate is dependent upon hormonal and nutritional status. On the other hand, normal glycosylation reaction occurs through the formation of a retinol-linked sugar complex. It is suggested that the relative drop of serum retinol levels, as a result of modified hormonal climate and/or declining protein status, might constitute a critical factor capable of inducing a defective incorporation of mannose into native thyroglobulin, leading to an early depression of the full glycoprotein production. This concept affords a comprehensive explanation of the following unresolved data recorded in goitrous areas: (1) clinical and biochemical discrepancies between subjects living in the same morbid territory, (2) persistence of endemicity in spite of appropriate iodine supplementation, (3) similar prevalence of goiter hypertrophy in male and female prepubertal children, (4) increased frequency of goiter enlargement in the four most vulnerable groups, namely preschool children of both sexes, adolescent girls, pregnant women, and elderly persons, (5) decreased impact of thyroid swelling accompanying improved socio-economic status, even without iodine addition, and (6) resurgence of goitrous hyperplasia as an effect of seasonal or sporadic deterioration of nutritional habits, even when iodine supply remains unchanged.

[Thyroid function in protein-caloric malnutrition in infants (author's transl)]. / Fonction thyroïdienne dans la malnutrition protéino-calorique chez l'enfant en bas âge.

Iodine kinetics and thyroid function were investigated in 68 cases of protein-caloric malnutrition (senegales children). This nutritional state induces an acute and severe alteration of thyroid function, as indicated by the reduced iodine uptake and clearance, a 50% decrease of hormonal secretion rate, and the low levels of total and free T4. T3 concentration is also very low: this may be partly due to a defective conversion of T4 to T3. Despite this state of primary hypothyroidism, no hypersecretion of TSH is observed.

Activity and subcellular distribution of protein kinase dependent on adenosine 3':5'-monophosphate in liver from normal and adrenalectomized rats.

We have examined whether glucocorticoids control the activity and (or) the subcellular distribution of protein kinase dependent on cyclic AMP (adenosine 3':5'-monophosphate), since they influence cyclic-AMP-dependent responses to other hormones. Protein kinase activity was determined in rat liver homogenates and subcellular fractions, nuclear, large granular, microsomal and supernatant obtained by differential sedimentation in 0.25 M sucrose. 63% of the tissue protein kinase activity detected in absence of cyclic AMP reside in the particulate fractions. Upon addition of exogenous cyclic AMP, protein kinase activity is stimulated 1.8, 1.2, 1.2 and 4.5-fold in nuclear, large granular, microsomal and supernatant fractions, respectively. Under these conditions, 66% of tissue activity are found in the supernatant fraction. The activity sensitive to exogenous cyclic AMP resolves into a major (84%) cytosoluble and a minor (16%) nucleomicrosomal component. The latter activity resists elution with isotonic saline and is increased in the presence of Triton X-100. Three groups of rats were studied: control and adrenalectomized with or without cortisol treatment. In whole liver homogenates, both protein kinase activity detected in absence of exogenous cyclic AMP and sensitivity of the enzyme to cyclic AMP were comparable in all groups. Moreover, the distribution patterns of proteins kinase activity amoung the fractions were essentially the same in all groups of animals, whether or not particles had been treated with Triton X-100. Finally, in cell-free experiments, glucocorticoids alone or in combination with their intracellular receptor did not modify protein kinase activity of rat liver. Thus the results reported do not support the possibility that glucocorticoids influence cyclic AMP-dependent protein kinase in rat liver. Yet, this study provides data, not available before, on subcellular distribution of this enzyme in rat liver.

Secretory activity of isolated thyroid adenomas.

The catabolic phase of thyroid secretion --thyroglubulin (Tg) uptake and hydrolysis, release of hormones--has been investigated in vitro, by incubating thyroid slices with 0.1% labelled Tg, in cases of isolated adenomas. Twenty-two specimens were examined: 11 cold follicular adenomas, 5 hot nodules from euthyroid patients, 2 untreated toxic adenomas, and 4 pretreated toxic adenomas. The results were compared with those obtained in 11 specimens of normal tissue. Tg pinocytosis (the amount of Tg taken up by the slices per mg of tissue) was severely impaired in all the non-toxic nodules, cold or hot, i.e., whatever the in vivo activity of the thyroid iodide pump. In toxic adenomas, every step of the catabolic hormonogenesis was activated: high pinocytotic activity, increased Tg hydrolysis, and the discharge of hormonal products; in pretreated cases, the whole process was slowed down. Enzymic activity of the acid hydrolases, beta-galactosidase and cathepsin, was elevated in all the nodules so far investigated, particularly in the toxic adenomas.

T3 resin uptake in protein-calorie malnutrition.

RT3U3) is significantly elevated (P less than 0.001) in the acute stage of kwashiorkor and returns to normal after 2 weeks of appropriate refeeding. RT3U is characterized by a high negative correlation with TBGcap. This negative correlation is maximal on admission (r equals -0.88) and gradually declines to normal value (r equals -0.63) with clinical recovery. This finding is consistent with the main role attributed to TBG in determining RT3U level. The collected data emphize the importance of the protein plasma levels in the evaluation of the thyroid function with RT3U in protein-calorie malnutrition.

Albumin, transferrin and the thyroxine-binding prealbumin/retinol-binding protein (TBPA-RBP) complex in assessment of malnutrition.

A comparative study of the level of 4 plasma proteins in malnutrition shows that albumin has low sensitivity, transferrin has intermediate and the TBPA-RBP complex has the highes sensitivity to an alteration in the nutritional status. According to protein and/or iron deficiency, the synthesis of trnasferrin seems to be submitted to contradictory impulses which partially invalidates this test as a reliable index for estimating protein depletion alone. On the contrary, the components of the TBPA-RBP complex respond together and in a parallel direction to protein deficiency. The high degree of sensitivity of TBPA and RBP to an inadequate protein intake is apparently related to their rapid turnover rate and to their unusual richness in tryptophan, which is known to play a key role in the control of protein synthesis. Measurement of TBPA (or RBP) is proposed as a method for the detection of pre-kwashiorkor and early marasmus.

Defective thyroglobulin endocytosis and hydrolysis in thyroid cold nodules.

The catabolic phase of thyroid secretion has been studied by incubating thyroid slices with 0.1 % 125-I thyroglobulin (Tg) in the following cases: 11 follicular adenomas (FA), 8 hyerplastic nodules in multinodular glands (NM), 3 carcinomas (follicular or papillary, FC, PC) and normal (N) or micronodular tissue (M). Tg pinocytosis is severely impaired in all cold nodules (25 to 60 % reduction). In the follicular tumours (FA, FC), Tg hydrolysis is more affected than would be expected based only on reduced Tg endocytosis: the hydrolysis products remain in the phagolysosomes instead of being secreted. As far as the acid hydrolases are concerned these enzymatic activities are increased in nearly all nodules, in particular in follicular adenomas and carcinomas.

The role of retinol-binding protein in protein-calorie malnutrition.

Plasma RBP is decreased to 1.62 mg plus or minus 0.71/100 ml, or 31.1 percent of normal, in the acute stage of kwashiorkor. RBP doubles its plasma level after 1 wk and triples after 2 wk of appropriate refeeding. The return to normal of RPB runs in close parallel with prealbumin (PA), implying that both components remain bound by 1:1 molar ratio in the PA-RBP complex. Low values recorded on admission for RBP seem to be the result of reduced liver biosynthesis. On the other hand, a high correlation persists between RBP and retinol plasma level along the successive steps of clinical recovery, suggesting that RBP acts as the limiting factor for retinol transport.

Discrepancy between the measurement of thyroxine-binding prealbumin plasma level and binding capacity in protein-calorie malnutrition.

The measurement of thyroxine-bindung prealbumin (TBPA) in protein-calorie malnutrition by two different techniques leads to the recognition of an unexpected discrepancy. Whereas TBPA plasma levels as measured by immunodiffusion are markedly decreased to 29.3% of the normal, those recorded by maximal binding capacity (TBPAcap) are characterized by a wide dispersion. In the control group, the ratio between TBPAcap and TBPA plasma level is 9.1. In the malnourished group on admission, the same ratio is 30.0. The possibility of a qualitative effect in the tetrameric TBPA structure, with the binding of additional thyroxine (T4) molecules on the secondary binding sites, has been investigated. This hypothesis has been discarded by Scatchard plot studies. The normal 1:1 molar ratio between TBPA and T4 is unaffected in protein-deficient patients. Discrepant results obtained for TBPAcap and TBPA levels appear to be the consequence of low plasma protein levels, leading to an artifact in the electrophoretic method.