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Dense sintered samples of Th1 − xUxO2 solid solutions were prepared from the initial precipitation of oxalate precursors through two different wet chemical routes, based either on the direct precipitation of the cations or on the use of hydrothermal method. For both low-temperature precursors, the specific surface area was followed versus the heating temperature and the influence of the conversion step on the oxide powder reactivity was evidenced since it allowed to obtain reactive surfaces in the range of 15–45 m2 g−1 without any additional grinding step. From dilatometric studies, the operating conditions required for the complete densification of the Th1 − xUxO2 pellets were set to a heat treatment of 3 h at 1500 °C. In these conditions, the density of the samples lies between 94% and 99% of the calculated value whatever the preparation method chosen which appeared very promising compared to the results already reported under inert atmosphere. The initial precipitation of low-temperature precursors thus allowed to lower the sintering temperature by about 100 °C while the use of hydrothermal conditions significantly improved the cationic distribution in the sintered samples, as shown from EPMA statistical experiments.

The $ \beta^{{+}}_{}$ /EC decay of 189m, gPb has been studied at the ISOLDE facility using nuclear spectroscopy and in-source laser spectroscopy. A level scheme of 189Tl has been built from $ \gamma$ - $ \gamma$ coincidence relationships and information on the feeding of some excited levels of 189Tl provided by the hyperfine spectra obtained from laser ionization. The half-lives of both the 13/2+ and 3/2- 189Pb isomers have been estimated to be T 1/2 = 50±3 s and T 1/2 = 39±8 s, respectively. Calculations have been performed for different oblate and prolate nuclear deformations using an axial-rotor coupled to one-quasiparticle model, a structure has been suggested for the low-lying levels of the 189Tl nucleus.

The iodination of Gorleben and synthetic humic substances (HS) was studied complementarily by UV-visible and X-ray Photoelectron Spectroscopy (XPS). The I2(aq) consumption kinetics could neither be linearly correlated to [H+] nor to HS concentration as already observed in the literature. Nevertheless, the electrophilic substitution mechanism was further evidenced by the production of both I3 - and I-, leading to a covalent bonding. The XPS analysis of the iodinated samples confirmed the covalent bonding between iodine and carbon of HS for all the samples.

RADIOCH; In the field of the long-term specific immobilization of actinides, thorium phosphate diphosphate (β-TPD), as potential candidate, must respond to several criteria. Among them, the material must present a good resistance to irradiation and keep its initial good properties such as resistance to aqueous alteration. In order to check this later point, sintered samples of β-TUPD solid solutions were pre-irradiated with ion beams with various conditions (fluence, stopping power) then submitted to leaching tests in different media (pH, temperature, complexing reagents, flow rate, ...). The normalized dissolution rates depend significantly on the amorphous fraction (increase by a factor of 10–100 between unirradiated and fully amorphized materials). On the contrary, the pre-irradiation of the samples does not affect the kinetic parameters of the dissolution such as the partial order relative to the proton concentration (n = 0.37 ± 0.01 and n = 0.34 ± 0.01 for unirradiated and fully amorphized samples, respectively) and the activation energy of the reaction of dissolution (Eapp = 49 ± 4 kJ mol−1 and Eapp = 42 ± 4 kJ mol−1 for unirradiated and partly amorphized samples (fA < 1), respectively).

Laser spectroscopy based on resonant ionization of laser-desorbed atoms has been used to study the neutron-rich tellurium isotopes with the COMPLIS facility at ISOLDE-CERN. Isotope shifts and hyperfine structures of several neutron-rich Te isotopes: $^{120−136}$Te and $^{123 m−133 m}$Te have been measured. From the hyperfine structure we have extracted magnetic and quadrupole moments. Changes in the mean square charge radii have been deduced and their comparison with the known data for the other elements near Z = 50 is presented. The experimental $\delta$ values are compared with those obtained from relativistic mean field calculations.

The release properties of UCx and molten U thick targets associated with a Nier–Bernas ion source have been studied. Two experimental methods are used to extract the release time. Results are presented and discussed for Kr, Cd, I and Xe.

This paper illustrates the potentialities and the innovative character of surface analysis techniques such as nuclear microprobe analysis (NMA) and X-ray photoelectron spectroscopy (XPS) in the research field of humic substances (HS), in particular to characterize HS/trace elements association. NMA showed its potentialities to characterize HS/ trace element associations at the microscopic scale and quantification of trace elements scavenged by humic acids (HA) and distribution and thickness of HA films sorbed onto silica surfaces after sorption tests. XPS was used to determine the chemical environment of iodine in natural HS. These techniques enabled us to establish association between HS colloids and numerous trace elements (both cations and anions, especially I) and to evidence a strong affinity of the smallest HA colloids (< 15 nm) for these elements. Moreover, associations between HS and I were clearly evidenced by NMA, through the study of the ternary system (SiO 2 /HA/I), as well as of natural HS. Chemical bonds implied in these associations may be of covalent character, as seen from XPS data. Combination of these techniques with Ion Coupled Plasma Mass Spectrometry (ICP-MS) was also necessary to analyze the aqueous solutions in contact with HS.

In order to confine specific long-life actinides, originating from high-level nuclear wastes, lanthanum aluminosilicate glasses are considered. The aqueous corrosion behavior of these glasses is studied under static conditions ( T=96 ° C, duration between one and six months, glass surface area/leachate volume, S/V=0.3, 50 and 500 cm−1) by means of solution analysis (ICP-MS and spectrophotometry) and solid analysis (X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry). Tests performed at high S/V ratio lead to silicon releases of 10−3 mol l−1 while lanthanum releases reach 10−4.5 mol l−1. Phosphate anions are found to modify the dissolution, as an amorphous lanthanide phosphate is evidenced at the glass surface after the corrosion experiment. The lanthanide releases decrease in presence of phosphate, but the matrix dissolution process is not reduced.

Nuclear microprobe by coupling the resonant nuclear reaction 12 C ( p , p ) 12 C and proton-induced X-ray emission (PIXE) at 1.725 MeV has showed its capabilities to study a ternary system silica slide/humic acids (HA)/iodine. The nuclear reaction on carbon-12 permits the determination of thickness (from 8 nm to 2.5 μm ) of HA films sorbed on mineral surfaces, whereas PIXE simultaneously allows the quantification of trace elements scavenged by HA. The results obtained on the ternary system have evidenced a heterogeneous distribution of HA onto silica slides (presence of organic clusters of variable thickness) and confirmed the trace elements/organic matter association. Moreover, the data suggest a role played by HA in the retention of iodine onto silica slide surfaces.

The solubility behavior of uranium dioxide was studied under oxidizing conditions in the Belgian Boom clay water at 25°C up to 323 days. X-ray photoelectron spectroscopy analyses reveal that both U(VI) and U(IV) oxidation states are present in the altered layer. The U(VI)/U(IV) ratio in this altered layer increases up to 43 days and then remains constant throughout the whole test. In the leachate the uranium concentration also increases up to 43 days and then stabilizes. It is rather unlikely that the altered layer formed on the surface controls thermodynamically the uranium solubility. It is rather probable that the system has reached a pseudo-equilibrium governed by kinetics.

The aqueous alteration behavior of glasses in the system Y–La–Al–Si–O–N has been investigated using the Soxlhet test. The altered surface was then studied by means of solid and solution analyses. In the case of La–Al–Si–O–N glasses, the formation of a crystallized lanthanum hydroxycarbonate was determined by X-ray diffraction (XRD) analysis. In the case of Y–La–Al–Si–O–N, X-ray photoelectron spectroscopy analysis (XPS) reveals a complete disappearance of silicon and aluminum at the glass surface (depth analyzed: 20 A). Rutherford backscattering spectrometry (RBS) gives some evidence that the glass surface is covered with a phase consisting mainly of yttrium and lanthanum compounds. Solution and solid analyses provide evidence that yttrium increases the chemical durability of the glass. Nitrogen seems to enhance glass corrosion by increasing the pH of the solution.

The aqueous corrosion behavior of lanthanide aluminosilicate glasses has been studied under static conditions (T=96°C, duration=1 and 3 months, glass surface area/leachate volume, S/V=0.3 cm−1) by means of solution and solid analyses. It was found that these glasses exhibit a high chemical durability. The influence of yttrium, magnesium and nitrogen, which are supposed to improve the mechanical properties, on the chemical durability, has been investigated. After a one-month experiment, lanthanum and yttrium releases were found to be about 10−7 mol l−1, while silicon and aluminum releases were about 10−5 mol l−1. Yttrium seems to improve the chemical durability. The presence of nitrogen does not seem to modify the glass constituents releases, but seems to improve the surface state of the altered glass. XPS experiments reveal that lanthanum and yttrium are more concentrated near the surface (20–30 A) of the glass after the leaching test.

Laser spectroscopy measurements have been carried out on very neutron-deficient isotopes of Au, Pt and Ir, produced as daughter elements from a Hg ISOLDE beam. For these transitional region nuclides, the hyperfine structure (HFS) and isotope shift (IS) were measured by Resonance Ionization Spectroscopy (RIS). Magnetic moments μ, spectroscopic quadrupole moments Qs and changes of the nuclear mean square charge radius δ〈rc 2〉along isotopic series have been extracted. For some results, a detailed comparison with theoretical predictions is presented.

Radioactive waste management is one of the major technical and scientific challenge to be solved by industrialized countries near the beginning of the 21st century. Relevant questions arise about the extrapolation of the long term-behavior of materials from waste package, engineered barriers and near field repository. Whatever the strategical option might be, wet atmosphere or water intrusion through the different barriers constitute the two main remobilization factors for radionuclides in the geosphere and the biosphere. The study of solid alteration processes and elemental sorption phenomena on mineral surfaces is one of the most efficient basic research approaches to assess the long term performance of waste materials. Ion beam analysis and more recently nuclear microprobe techniques have been applied to investigate exchange mechanisms near representative solid/liquid interfaces such as glass/deionized water, uranium dioxide/granitic or clay water or mineral surface/aqueous solution doped with chemical elements analogue to actinide or fission products. This paper intends to describe the different works that have been carried out in Saclay using the nuclear microprobe facility. The coupling of μRBS, μPIXE and μNRA permits to determine the evolution of the surface composition induced by chemical reactions involved. Complementary observation of solid morphology and solution analysis allows to obtain a complete elemental balance on exchange processes.

The g factors of three high spin isomers in 187,189,191Au have been measured, using the time differential perturbed angular distributions. The reactions used and the results obtained for the g factors and the lifetimes are: 172Yb(19F, 4nγ) 187Au, g (31/2- or 35/2-) = 0.25 (3), T1/2 = 102 (5) ns; 181Ta ( 12C, 4nγ) 189Au, g (31/2+) = 0.42 (2), T1/2 = 242 (10) ns; and 176Yb(19F, 4nγ) 191Au, g (31/2+) = 0.42 (3) T1/2 = 402 (20) ns. These results show that the structure of these isomers is consistent with a 1 proton, 2 neutrons structure. The experimental set-up was cheked by measuring the g factor of the Coulomb excited 197 keV, T1/2 = 89.3 ns level of the 19F beam stopped in the lead backing.

A metalloendopeptidase that selectively cleaves doublets of basic amino acids on the amino-terminal side of arginine residues was purified to homogeneity from rat testes and analyzed further. Two catalytically active forms with apparent relative molecular masses of 110,000 and 140,000 Da, respectively, were present in the purified preparation of the enzyme. Antibodies raised against the purified testis endopeptidase revealed by immunoblot both the 110- and 140-kDa forms in both rat testis and brain cortex extracts. The isolated enzyme was inhibited by metal chelators and divalent cations. Its activity, lost after preincubation with EDTA, was restored by low concentrations of Zn2+ and Mn2+, thus demonstrating the metallopeptidase nature of the enzyme. This endopeptidase also exhibited a high sensitivity to amastatin (100% inhibition at 20 microM), an aminopeptidase inhibitor. A substrate specificity study using physiologically important or synthetic peptides containing a processing dibasic site indicated that cleavage occurred selectively at the amino-terminal side of an arginine residue, independent of the nature of the basic doublet. The enzyme produced such a cleavage at the Arg-Lys doublet of somatostatin 28 (Km = 43 microM), at the Arg-Arg doublet of dynorphin A (Km = 6.45 microM) and atrial natriuretic factor (Km = 6.25 microM), and at the Lys-Arg doublet of preproneurotensin-(154-170) (Km = 17.3 microM). Moreover, cleavage efficiency was found to be higher for the larger substrates. The distinctive properties of this endopeptidase imply that this protein is a member of a novel class of proteolytic enzymes that may be involved in the endoproteolytic maturation of hormonal precursors.

The endoproteolytic activity previously detected in rat intestinal mucosal extracts (Beinfeld M., Bourdais, J., Kuks, P., Morel, A., and Cohen, P. (1989) J. Biol. Chem. 264, 4460-4465), was purified to homogeneity as a 65-kDa molecular species. This putative proprotein-processing enzyme cleaves the peptide bond on the carboxyl side of a single arginine residue in hepta-[Leu62-Gln-Arg-Ser-Ala-Asn-Ser68] or trideca-[Asp56-Glu-Met-Arg-Leu-Glu-Leu-Gln-Arg-Ser-Ala-Asn-+ ++Ser68] peptides, reproducing the prosomatostatin sequence around Arg64, the locus for endoproteolytic release of either somatostatin-28 or its NH2-terminal fragment, somatostatin-28-(1-12), from their common precursor. This enzyme exhibits a strict selectivity for arginyl residues, as demonstrated with related substrates, and did not cleave at lysyl residues. Moreover, only arginyl residues belonging to peptides of the prosomatostatin family were cleaved, since no hydrolysis of peptides from other prohormones was detected. In addition, the arginine residue situated at position -5 on the NH2-terminal side of Arg64 not only did not function as a cleavage locus, but had no effect on the overall cleavage kinetics of the prosomatostatin-(56-68) peptide substrate. This enzyme also cleaved, but with much less efficiency, the peptide bond on the carboxyl side of an arginine in peptides containing either an Arg-Lys or a Lys-Arg doublet corresponding to prohormone cleavage sites. This enzyme was insensitive to divalent cation chelators, was completely inhibited by aprotinin and leupeptin, and was somewhat inhibited by other serine-protease inhibitors. It is concluded that this endoprotease is a serine protease and could be involved in prohormone or proprotein post-translational processing at single arginine cleavage sites.

The shape of exotic even-mass (182-190)Pb isotopes was probed by measurement of optical isotope shifts providing mean square charge radii (delta(r(2))). The experiment was carried out at the isolde (cern) on-line mass separator, using in-source laser spectroscopy. Small deviations from the spherical droplet model are observed, but when compared to model calculations, those are explained by high sensitivity of delta(r(2)) to beyond mean-field correlations and small admixtures of intruder configurations in the ground state. The data support the predominantly spherical shape of the ground state of the proton-magic Z=82 lead isotopes near neutron midshell (N=104).

Two field experiments were conducted to evaluate the efficiency of Rusa deer in the development of the cattle tick Boaphilus microplus in comparison with that of steers in the same pastures and under the same conditions of infestation. No difference was noted between a mixed steer/deer herd and a pure steer or pure deer herd in the infestation pattern of each host, suggesting that attachment to the alternative host is mechanical and not affected by the simultaneous presence of the primary host on the pasture. Deer are capable of producing engorged viable females, with weight and reproductive performances similar to or even better than females fed on steers. For moderate levels (1 million larvae per hectare) and high levels (32 million larvae per hectare) of pasture infestation, tick burdens on steers were not very different (e.g. average 1,911 and 2,681 ticks per m2 skin, respectively, on day 24). This may be because of saturation of steer skin sites at the moderate larval dose. Deer harboured 2.7-33 times fewer ticks than steers and produce no engorged females at the moderate larval level and 32 times fewer engorged females than steers at the high larval level. Infestation of deer was dose-dependent with averages of 12 and 399 ticks per m2 skin on day 25 at the moderate and high larval levels, respectively. At a high infestation level of the environment, Rusa deer may contribute, but to a limited extent, to infestation of pastures and, consequently, of cattle. However, their role in sustaining a viable tick population requires further investigation.

Under retinoic acid exposure, the three SK-N-BE(2)-derived human neuroblastoma cell lines, BE(2)-NA, BE(2)-SA and BE(2)-M17 undergo mainly differentiation, apoptosis or continue to proliferate, respectively. We have used this model system to study the modulation of the transcriptional expression of putative processing enzymes, two novel metallopeptidases; i.e. N-arginine dibasic convertase (NRD convertase; EC 3.4,24,61) and an aminopeptidase-B after exposure of the cells either to retinoic acid or to synthetic retinoid analogs. The data indicate that the two respective enzymes are differently modulated in the various cell lines. Whereas aminopeptidase-B expression is enhanced in most cases, NRD convertase appears to undergo opposite regulation in proliferating versus differentiating neuroblastoma cells. It is concluded that both genes might contain retinoic acid regulatory elements (RARE) in their promoters.

The tropical bont tick, Amblyomma variegatum, is an African tick species which infests livestock and wildlife. It was probably introduced in the central eastern islands of the Caribbean during the 18th or 19th century, with cattle shipped from Senegal. In Africa and the Caribbean, this tick is a vector of heartwater (a rickettsial disease of ruminants) and is associated with acute dermatophilosis (a bacterial skin disease of animals). Until 1948, only Guadeloupe and the neighbouring islands of Marie Galante and Antigua were infested with this tick species. Following increased agricultural commerce between Guadeloupe and Martinique, the latter became infested in 1948. Between 1967 (when the tick was identified in St Croix) and 1988 (when a male tick was reported in St Vincent), fourteen new islands were reached by this tick. Most of the dissemination of the tick to new islands cannot be explained by legal or illegal movements of livestock. Recently-determined circumstantial evidence strongly links the increase in populations of the cattle egret (Bubulcus ibis), a migrating bird established in the Caribbean circa 1960, with increased colonisation of new islands by A. variegatum. Considering the wide range of areas currently occupied by this bird species in the Greater Antilles and on the American mainland, there is a high probability that the tick will also expand its range and invade new areas. Eradication of A. variegatum from the Caribbean and thus from the western hemisphere, and the strengthening of measures to prevent inter-island movements of livestock, would be the only effective means of preventing this threat.

A metalloendopeptidase that selectively cleaves doublets of basic amino acids on the amino-terminal side of arginine residues was purified to homogeneity from rat testes and analyzed further. Two catalytically active forms with apparent relative molecular masses of 110,000 and 140,000 Da, respectively, were present in the purified preparation of the enzyme. Antibodies raised against the purified testis endopeptidase revealed by immunoblot both the 110- and 140-kDa forms in both rat testis and brain cortex extracts. The isolated enzyme was inhibited by metal chelators and divalent cations. Its activity, lost after preincubation with EDTA, was restored by low concentrations of Zn2+ and Mn2+, thus demonstrating the metallopeptidase nature of the enzyme. This endopeptidase also exhibited a high sensitivity to amastatin (100% inhibition at 20 microM), an aminopeptidase inhibitor. A substrate specificity study using physiologically important or synthetic peptides containing a processing dibasic site indicated that cleavage occurred selectively at the amino-terminal side of an arginine residue, independent of the nature of the basic doublet. The enzyme produced such a cleavage at the Arg-Lys doublet of somatostatin 28 (Km = 43 microM), at the Arg-Arg doublet of dynorphin A (Km = 6.45 microM) and atrial natriuretic factor (Km = 6.25 microM), and at the Lys-Arg doublet of preproneurotensin-(154-170) (Km = 17.3 microM). Moreover, cleavage efficiency was found to be higher for the larger substrates. The distinctive properties of this endopeptidase imply that this protein is a member of a novel class of proteolytic enzymes that may be involved in the endoproteolytic maturation of hormonal precursors.

The success of an eradication campaign against the tropical bont tick in the Caribbean imposes the use of active acaricide compounds, if possible with residual activity, easy to apply and requiring few or no accessible water supplies and expensive application equipment. Tests of in vitro susceptibility of tick strains from Puerto Rico and Guadeloupe as well as observations of the impact of the current tick control campaigns conducted in some Caribbean islands, seem to indicate that there is no problem of resistance to acaricides. Pyrethroid acaricides have an advantage since they are active at very low concentration levels and have a low toxicity for mammals and to the environment. Some of them are in a pour-on formulation which allows for rapid application and complete coverage of the whole body of the animal. A withdrawal period is not necessary. However, improvements must be found to facilitate the application onto the back of cattle that, for the majority in the Caribbean, are tethered and not perfectly restrained. A spot-on application method with a drench gun seems more adapted to tethered animals than the pour-on. For small ruminants and dogs but also for cattle, slow release devices impregnated with acaricides may be useful in reducing the frequency of animal treatments. However, experiments on goats with collars impregnated with flumethrin indicate an efficiency of less than 55 days, insufficient to justify their use on a large scale in an eradication program.

Amblyomma variegatum (Fabricius), the tropical bont tick, is now widely distributed in the Caribbean. Eighteen islands countries are now or were recently infested with the tick. To stop the spread of this tick to other non-infested islands and to the mainland areas of South, Central and North America, a regional eradication program has been proposed and endorsed by the respective governments on each of the Amblyomma variegatum infested islands, including the French government and CARICOM member and associate member countries. The Food and Agriculture Organization of the United Nations (FAO) was requested by CARICOM, on behalf of member and associate member governments to: develop eradication proposals; assist CARICOM member countries to maintain existing Amblyomma tick control programs; advise and assist with the drafting of legislation required for implementation of an eradication program; assist in the identification of funds to implement the eradication program and, if funding was obtained, coordinate the eradication campaign against this tick on all infested islands. The current distribution of the tick and the status of the proposed eradication program in the Caribbean are discussed.

A severe outbreak of dermatophilosis occurred in 1985 in a herd of Brahman cows imported from Martinique in Guadeloupe in July 1983. Little was known on this disease in Guadeloupe until then, for the local zebu breed is naturally highly resistant to diseases transmitted by ticks or associated with them. Conditions of appearance and development of the disease were studied in relation with herd management, climate and treatments applied. There was no evidence of the disease during the first 6 months following the importation, in a feedlot management. The first lesions of dermatophilosis appeared about 2 months after the animals were allowed to graze on pastures infested with ticks. Then, thirty percent of the herd became infected. Development of the infection increased dramatically as the humid season approached, and all the 29 Brahman cows showed lesions in July 1985. Only drastic treatments, including antibiotics and local disinfection, associated with the removal from pastures into covered stables allowed the recovery from the disease. Nevertheless, the disease caused the death of 13 head. Differences in individual reactions were also noted, and 7 different types of evolution were identified. These observations provided informations about the epidemiology of dermatophilosis in the climatic conditions of Caribbean humid tropics. They showed the economic importance of this severe disease for cattle in the region and the sensitivity of exotic breeds.

Amblyomma variegatum, introduced into Guadelopue 150 years ago, has recently spread in the Lesser Antilles and threatens North America. Two important diseases are associated with the tick: heartwater and dermatophilosis. Heartwater occurs in Guadeloupe, Marie-Galante and Antigua; acute dermatophilosis exists almost everywhere the tick is present. Both are very pathogenic for upgraded or newly-infested cattle. After 15 years of A. variegatum control in Guadeloupe, a balance is established between a tick population maintained at a low level by spraying acaricides and an animal population either completely resistant to heartwater and dermatophilosis (creole cattle) or regularly treated against ticks (upgraded cattle). An eradication campaign against A. variegatum in Guadeloupe, to avoid the spread of the associated diseases, appears technically difficult but possible, economically profitable, but socially completely utopian. We suggest for Guadeloupe a reinforced control of the tick with a persistent acaricide, hoping that a general decrease of the tick infestation rate on cattle will eliminate heartwater and acute dermatophilosis.

Experiments were conducted with Creole goats and Amblyomma variegatum ticks in Guadeloupe to investigate whether it is possible to transmit Cowdria ruminantium to susceptible hosts with nymphs fed in the larval stage on recovered goats. Of 88 batches of larvae fed after the return of the goats' temperature to normal, or after challenge or immunosuppression, only the 9 batches of larvae fed during the febrile reaction, 2 batches applied 2 and 3 days respectively after recovery, and a single batch applied 5 days after challenge, became infective. On average, blood appears to be infective for A. variegatum larvae for only an 8-day period associated with the temperature reaction following a primary infection. Recovered goats are not reservoirs of Cowdria, even if--with one exception in our experiment--they are reinfected after recovery.

The resistance rate of different populations of the same breed of creole Guadeloupean goats to Cowdria ruminantium infection varied greatly depending on the previous heartwater history of each population. After experimental infection of goats removed decades ago from endemic areas, the observed resistance rate was 25%, while it was 54% in a population that had been isolated from the disease for 10 years and reached 78% in a flock actually exposed to heartwater. This resistance seems to be under genetic control as sex and paternity were the most important factors which could explain resistance in a group of 90 kids of the same flock, tested under controlled conditions. Resistance rate varied greatly (20-83%) depending on the sire, with a heritability estimate of 0.49 for half sibs and 0.85 for full sibs. A recessive sex-linked gene could be involved in the genetic determination of this resistance. From these observations, it can be stated that in endemic heartwater areas, each population, i.e. each flock, will have developed resistance at a definite rate according to population, age and the extent of past and present exposure to the disease, through a natural selection of resistant lines. Populations removed from exposure to heartwater will progressively lose their ability to resist infection through an increase in the frequency of susceptible stock. If our hypothesis of a recessive sex-linked gene is proved correct, it should be easy to select for improved resistance to the Guadeloupe breed of goat to heartwater.

The existence of heartwater on 3 islands of the Central Lesser Antilles and the presence of an efficient vector originating from Africa, Amblyomma variegatum, on most of the islands of this region constitute a serious threat for livestock on the American mainland. The disease can be introduced there either by infected animals or infected ticks. The most likely way is probably the transportation of domestic animals which are heavily infested by ticks. Due to the low rate of infection of ticks in endemic areas and the low rate of infestation of wild animals by ticks, the risk of transportation by migratory birds (among which the cattle egret is the most important) seems negligible compared with domestic animals, especially ruminants and dogs. The establishment and spread of the disease on the mainland could result from indigenous American Amblyomma species, of which at least 2, Amblyomma cajennense and, more especially, Amblyomma maculatum, are experimental vectors. The biological and ecological features of these ticks conform to some extent with the characteristics necessary for them to act as vectors. They are widespread and sufficiently well adapted to ruminants to ensure the continuation of the epidemiological cycle. Disease could evolve in wild life (deer) or, as seems more likely, in livestock, of which the population density is very high on most of the mainland. However, the establishment of the disease is more likely to occur if the well adapted vector of heartwater, Amblyomma variegatum, is introduced as well. This exotic species would find environmental conditions favourable for its survival and spread in most of the tropical and subtropical Western Hemisphere. Protection of the American mainland and the disease-free islands of the area must be based on strict control of domestic animal movement in the Caribbean, on the decrease of the vector population by tick control campaigns and, if possible, on the eradication of Amblyomma variegatum from the focus of heartwater on the islands.

At present, heartwater in the Caribbean is known with certainty only on Guadeloupe, Marie Galante and Antigua; the first 2 islands are widely infected. The most important factors responsible for particular aspects of heartwater in Guadeloupe are: Cowdria ruminantium of high virulence. A very resistant cattle population (Creole), not normally clinically affected. A fairly susceptible goat population (Creole) (22% goats born in endemic areas die after experimental inoculation) which, fortunately, includes breeding lines with inherited resistance characteristics. Amblyomma variegatum which is present all over the island and all through the year, but with a low infection rate (1-2% of adult ticks are infected) because of the short period of rickettsemia in infected animals. The low rate of tick infection results in a low endemicity of the disease. For goats, the epidemiologic situation can be regarded as unstable because the low rate of infection in ticks does not allow a natural immunization of the majority of young kids when they still have a non-specific resistance. The possible evolution of heartwater in the Caribbean and in the United States in considered.

A presumptive diagnosis of heartwater in the living animal can be based on clinical and epidemiologic observations. In Guadeloupe, heartwater can be confused with haemonchosis in goats or cerebral babesiosis in cattle. Confirmation of the clinical diagnosis by brain biopsy is useful in experimental infections but is hardly applicable in the field. Positive results were obtained from 92% of animals 16 to 18 days after experimental infection. In febrile animals the best results were obtained between the 3rd and 6th days of the thermal response. Diagnosis can also be supported by serological tests. These are useful for monitoring experimental infections and for checking recovered animals in the field. Nineteen goats out of 27 were negative on Day 1 of the febrile reaction but positive a week later. The remaining 8 goats were positive on Day 1 and had greatly increased antibody titres a week later. Confirmation of a diagnosis can also be achieved by subinoculating into susceptible animals either blood or suspensions of ticks collected from suspect animals and then homogenized. Ticks that have engorged on a suspect animal can be allowed to moult and then fed on a susceptible animal to test their infectivity. These methods are time consuming but useful for heartwater surveys.