RESUMO
Peste des petits ruminants virus (PPRV) causes a contagious disease of high morbidity and mortality in global sheep and goat populations. To better control this disease and inform eradication strategies, an improved understanding of how PPRV transmission risk varies by age is needed. Our study used a piece-wise catalytic model to estimate the age-specific force of infection (FOI, per capita infection rate of susceptible hosts) among sheep, goats, and cattle from a cross-sectional serosurvey dataset collected in 2016 in Tanzania. Apparent seroprevalence increased with age, reaching 53.6%, 46.8%, and 11.6% (true seroprevalence: 52.7%, 52.8%, 39.2%) for sheep, goats, and cattle, respectively. Seroprevalence was significantly higher among pastoral animals than agropastoral animals across all ages, with pastoral sheep and goat seroprevalence approaching 70% and 80%, respectively, suggesting pastoral endemicity. The best fitting piece-wise catalytic models merged age groups: two for sheep, three for goats, and four for cattle. The signal of these age heterogeneities were weak, except for a significant FOI peak among 2.5-3.5-year-old pastoral cattle. The subtle age-specific heterogeneities identified in this study suggest that targeting control efforts by age may not be as effective as targeting by other risk factors, such as production system type. Further research should investigate how specific husbandry practices affect PPRV transmission.
Assuntos
Peste dos Pequenos Ruminantes/epidemiologia , Peste dos Pequenos Ruminantes/transmissão , Vírus da Peste dos Pequenos Ruminantes/genética , Fatores Etários , Animais , Bovinos , Doenças dos Bovinos/epidemiologia , Doenças dos Bovinos/virologia , Estudos de Coortes , Feminino , Doenças das Cabras/epidemiologia , Doenças das Cabras/virologia , Cabras , Masculino , Vírus da Peste dos Pequenos Ruminantes/imunologia , Estudos Soroepidemiológicos , Ovinos , Doenças dos Ovinos/epidemiologia , Doenças dos Ovinos/virologia , Tanzânia/epidemiologiaRESUMO
Peste des petits ruminants virus (PPRV) causes a contagious disease of high morbidity and mortality in small ruminant populations globally. Using cross-sectional serosurvey data collected in 2016, our study investigated PPRV seroprevalence and risk factors among sheep, goats and cattle in 20 agropastoral (AP) and pastoral (P) villages in northern Tanzania. Overall observed seroprevalence was 21.1% (95% exact confidence interval (CI) 20.1-22.0) with 5.8% seroprevalence among agropastoral (95% CI 5.0-6.7) and 30.7% among pastoral villages (95% CI 29.3-32.0). Seropositivity varied significantly by management (production) system. Our study applied the catalytic framework to estimate the force of infection. The associated reproductive numbers (R0) were estimated at 1.36 (95% CI 1.32-1.39), 1.40 (95% CI 1.37-1.44) and 1.13 (95% CI 1.11-1.14) for sheep, goats and cattle, respectively. For sheep and goats, these R0 values are likely underestimates due to infection-associated mortality. Spatial heterogeneity in risk among pairs of species across 20 villages was significantly positively correlated (R2: 0.59-0.69), suggesting either cross-species transmission or common, external risk factors affecting all species. The non-negligible seroconversion in cattle may represent spillover or cattle-to-cattle transmission and must be investigated further to understand the role of cattle in PPRV transmission ahead of upcoming eradication efforts.
Assuntos
Transmissão de Doença Infecciosa/estatística & dados numéricos , Doenças das Cabras/epidemiologia , Peste dos Pequenos Ruminantes/epidemiologia , Vírus da Peste dos Pequenos Ruminantes/isolamento & purificação , Doenças dos Ovinos/epidemiologia , Agricultura , Animais , Bovinos , Estudos Transversais , Países em Desenvolvimento , Cabras , Humanos , Incidência , Peste dos Pequenos Ruminantes/diagnóstico , Estudos Retrospectivos , Medição de Risco , Estudos Soroepidemiológicos , Ovinos , Tanzânia/epidemiologiaRESUMO
Transmission success for helminths with free-living stages depends on the ability of eggs and larvae to develop and survive once in the environment. While environmental conditions are often suggested to influence egg phenology and hatching rate, immunity against parasite eggs might also play a role. We examined this hypothesis using the gastrointestinal helminths Trichostrongylus retortaeformis and Graphidium strigosum, two common infections of the European rabbit. Changes in egg hatching rate and volume were examined in relation to specific antibodies in the serum and bound to eggshells, using eggs shed in host faeces over a 15-week period. Hatching rate was consistently higher for T. retortaeformis than G. strigosum and no changes were observed between weeks. Egg volume increased for G. strigosum but decreased for T. retortaeformis. We did find evidence of egg-specific antibody responses and fewer antibodies were bound to eggs of T. retortaeformis compared to G. strigosum. Little to no association was found between antibodies and hatchability, or volume, for both helminths. We suggest that host antibodies play a relatively minor role in the egg hatching rate of these gastrointestinal helminths.
Assuntos
Helmintíase Animal/imunologia , Helmintos/fisiologia , Óvulo/fisiologia , Coelhos , Animais , Helmintíase Animal/parasitologia , MasculinoRESUMO
Given their global distribution and abilities to persist in the host, helminths can play a crucial role in affecting risk of infections by increasing individual variation in infection. Helminth co-infections are of particular interest because by altering host immune responses, they can modify host susceptibility and thus intensity and transmission of other parasites/pathogens. The dynamics of co-infection were examined using two helminths of the European rabbit. Individuals were simultaneously challenged with a primary dose of both parasites, and changes in intensity were examined in relation to local and systemic immune responses. Both helminths persisted in co-infected rabbits; however, contrasting dynamics and immune responses were observed. Graphidium strigosum intensity was high throughout the co-infection, while Trichostrongylus retortaeformis intensity decreased but was not completely cleared. A Th2 response was observed against G. strigosum, while a mixed Th1/Th2 profile was found to T. retortaeformis. A comparison with our previous work on single infections showed that G. strigosum intensity was higher in co-infected than single infected hosts, while T. retortaeformis showed no significant changes. Differences were also observed in the cytokine profiles, blood cell concentrations and antibody trends. Overall, host variability during helminth co-infections can be generated by significant differences in immune responses and/or parasite dynamics.
Assuntos
Coinfecção , Tricostrongiloidíase/complicações , Tricostrongiloidíase/imunologia , Tricostrongilose/complicações , Tricostrongilose/imunologia , Animais , Anticorpos Anti-Helmínticos/análise , Citocinas/metabolismo , Suscetibilidade a Doenças , Imunoglobulina A Secretora/análise , Imunoglobulina G/análise , Intestino Delgado/imunologia , Intestino Delgado/parasitologia , Contagem de Leucócitos , Carga Parasitária , Coelhos , Estômago/imunologia , Estômago/parasitologia , Trichostrongyloidea/imunologia , Trichostrongyloidea/fisiologia , Tricostrongiloidíase/parasitologia , Tricostrongilose/parasitologia , Trichostrongylus/imunologia , Trichostrongylus/fisiologiaRESUMO
The host response to different helminth species can vary and have different consequences for helminth persistence. Often these differences are generated by changes in the dynamics and intensity of the immune components against parasites with distinct life history strategies. We examined the immune response of rabbits to primary infections of the gastrointestinal nematodes Trichostrongylus retortaeformis and Graphidium strigosum under controlled conditions for 120 days post-challenge. Results showed that rabbits developed a robust and effective immune response against T. retortaeformis and abundance quickly decreased in the duodenum and was completely cleared in the remaining sections of the small intestine within 4 months. Infected individuals exhibited an initial strong inflammatory response (IFN-γ), IL-4 expression also increased and was coupled to a rapid serum and mucus IgG and IgA and eosinophilia. Strong IL-4, serum IgA and IgG responses and eosinophilia were also observed against G. strigosum. However, parasite abundance remained consistently high throughout the infection, and this was associated with relatively low mucus antibodies. These findings suggest that immunity plays a key role in affecting the abundance of these nematodes, and different immune mechanisms are involved in regulating the dynamics of each infection and their long-term persistence in free-living host populations.
Assuntos
Doenças dos Roedores/imunologia , Trichostrongyloidea/imunologia , Trichostrongyloidea/patogenicidade , Tricostrongiloidíase/veterinária , Animais , Anticorpos Anti-Helmínticos/sangue , Modelos Animais de Doenças , Eosinofilia , Imunoglobulina A/sangue , Imunoglobulina G/sangue , Interferon gama/metabolismo , Interleucina-4/metabolismo , Intestino Delgado/patologia , Coelhos , Doenças dos Roedores/patologia , Fatores de Tempo , Tricostrongiloidíase/imunologia , Tricostrongiloidíase/patologiaRESUMO
Understanding seasonal changes in age-related incidence of infections can be revealing for disentangling how host heterogeneities affect transmission and how to control the spread of infections between social groups. Seasonal forcing has been well documented in human childhood diseases but the mechanisms responsible for age-related transmission in free-living and socially structured animal populations are still poorly known. Here we studied the seasonal dynamics of Bordetella bronchiseptica in a free-living rabbit population over 5 years and discuss the possible mechanisms of infection. This bacterium has been isolated in livestock and wildlife where it causes respiratory infections that rapidly spread between individuals and persist as subclinical infections. Sera were collected from rabbits sampled monthly and examined using an ELISA. Findings revealed that B. bronchiseptica circulates in the rabbit population with annual prevalence ranging between 88% and 97%. Both seroprevalence and antibody optical density index exhibited 1-year cycles, indicating that disease outbreaks were seasonal and suggesting that long-lasting antibody protection was transient. Intra-annual dynamics showed a strong seasonal signature associated with the recruitment of naive offspring during the breeding period. Infection appeared to be mainly driven by mother-to-litter contacts rather than by interactions with other members of the community. By age 2 months, 65% of the kittens were seropositive.
Assuntos
Infecções por Bordetella/veterinária , Bordetella bronchiseptica/imunologia , Cruzamento , Surtos de Doenças , Animais , Anticorpos Antibacterianos/sangue , Infecções por Bordetella/epidemiologia , Infecções por Bordetella/microbiologia , Infecções por Bordetella/transmissão , Doença Crônica , Ensaio de Imunoadsorção Enzimática , Feminino , Incidência , Transmissão Vertical de Doenças Infecciosas , Masculino , Coelhos , Estudos SoroepidemiológicosRESUMO
Free-living animals are usually inhabited by a community of parasitic species that can interact with each other and alter both host susceptibility and parasite transmission. In this study we tested the prediction that an increase in the gastrointestinal nematode Heligmosomoides polygyrus would increase the infestation of the tick Ixodes ricinus, in free-living yellow-necked mice, Apodemus flavicollis. An extensive cross-sectional trapping survey identified a negative relationship between H. polygyrus and I. ricinus counter to the prediction. An experimental reduction of the nematode infection through anthelmintic treatment resulted in an increase in tick infestation, suggesting that this negative association was one of cause and effect. Host characteristics (breeding condition and age) and habitat variables also contributed to affect tick infestation. While these results were counter to the prediction, they still support the hypothesis that interactions between parasite species can shape parasite community dynamics in natural systems. Laboratory models may act differently from natural populations and the mechanism generating the negative association is discussed.
Assuntos
Ixodes/patogenicidade , Murinae/parasitologia , Nematospiroides dubius/patogenicidade , Doenças dos Roedores , Infecções por Strongylida , Infestações por Carrapato , Animais , Feminino , Interações Hospedeiro-Parasita , Ixodes/crescimento & desenvolvimento , Masculino , Nematospiroides dubius/crescimento & desenvolvimento , Dinâmica Populacional , Doenças dos Roedores/imunologia , Doenças dos Roedores/parasitologia , Infecções por Strongylida/complicações , Infecções por Strongylida/parasitologia , Infecções por Strongylida/veterinária , Infestações por Carrapato/complicações , Infestações por Carrapato/parasitologia , Infestações por Carrapato/veterináriaRESUMO
Host-mediated responses and parasite density-dependent processes can have a major influence on the growth and fecundity of parasitic nematodes. However, host characteristics and parasite intensity consistently change during the course of an infection and these could affect worm length and number of eggs in a non-constant way. We used a free-living population of rabbits naturally infected with Trichostronglyus retortateformis and examined how adult nematode length and the number of eggs in utero were affected by host characteristics (i.e. age, sex, breeding status) and parasite intensity, in a seasonal environment, between 2004 and 2007. Nematode length and number of eggs in utero decreased exponentially with host age; in contrast, parasite intensity increased, peaked in juveniles and decreased in older hosts. These patterns were consistent between rabbit cohorts. A negative relationship was observed between parasite intensity and nematode length, as well as number of eggs. Nematode length was strongly affected by nematode sex and host age, while the number of eggs was mainly influenced by nematode length. The direct influence of host-mediated effects appeared quantitatively more important than parasite density dependence in controlling length and egg production in naturally infected wild rabbits. However, their relative contribution changed during the course of the infection such that, while host immunity still influenced worm numbers, the direct effect of density-dependent interactions contributed the most at high parasite intensities.
Assuntos
Fertilidade/fisiologia , Interações Hospedeiro-Parasita/fisiologia , Tricostrongilose/veterinária , Trichostrongylus/fisiologia , Fatores Etários , Animais , Tamanho Corporal , Feminino , Modelos Lineares , Masculino , Contagem de Ovos de Parasitas , Densidade Demográfica , Estações do Ano , Tricostrongilose/parasitologia , Trichostrongylus/crescimento & desenvolvimentoRESUMO
We examined the hypothesis that the interaction between concomitant infecting parasites modifies host susceptibility, parasite intensity and the pattern of parasite distribution within the host population. We used a 26 year time series of three common parasites in a natural population of rabbits: two gastrointestinal nematodes (Trichostrongylus retortaeformis and Graphidium strigosum) and the immunosuppressive myxoma virus. The frequency distribution of nematodes in the host population and the relationship between host age and nematode intensity were explored in rabbits with either single or dual nematode infections and rabbits infected with the nematodes and myxoma virus. The aggregation of T. retortaeformis and G. strigosum among the rabbits varied with the nature of the co-infection both in male and female hosts. The two nematodes exhibited different age-intensity profiles: G. strigosum intensity increased exponentially with host age while T. retortaeformis intensity exhibited a convex shape. The presence of a secondary infection did not change the age-intensity profile for G. strigosum but for T. retortaeformis co-infection (either both nematodes or myxoma-nematodes) resulted in significantly greater intensities in adult hosts. Results suggest that multi-species infections contributed to aggregation of parasites in the host population and to seasonal variation in intensity, but also enhanced differences in parasitism between sexes. This effect was apparent for T. retortaeformis, which appears to elicit a strong acquired immune response but not for G. strigosum which does not produce any evident immune reaction. We concluded that concomitant infections mediated by host immunity are important in modifying host susceptibility and influencing heterogeneity amongst individual hosts.
Assuntos
Enteropatias Parasitárias/imunologia , Infecções por Nematoides/imunologia , Fatores Etários , Animais , Suscetibilidade a Doenças , Feminino , Interações Hospedeiro-Parasita , Masculino , Myxoma virus , Mixomatose Infecciosa/imunologia , Parasitologia/métodos , Coelhos , Estações do Ano , Fatores Sexuais , Tricostrongilose/imunologia , TrichostrongylusRESUMO
Levels of parasitism and the dynamics of helminth systems is subject to the impact of environmental conditions such that we may expect long term increases in temperature will increase the force of infection and the parasite's basic reproduction number, R0. We postulate that an increase in the force of infection will only lead to an increase in mean intensity of adults when adult parasite mortality is not determined by acquired immunity. Preliminary examination of long term trends of parasites of rabbits and grouse confirm these predictions. Parasite development rate increases with temperature and while laboratory studies indicate this is linear some recent studies indicate that this may be non-linear and would have an important impact on R0. Warming would also reduce the selective pressure for the development of arrestment and this would increase R0 so that in systems like the grouse and Trichostrongylus tenuis this would increase the instability and lead to larger disease outbreaks. Extreme climatic events that act across populations appear important in synchronizing transmission and disease outbreaks, so it is speculated that climate disruption will lead to increased frequency and intensity of disease outbreaks in parasite populations not regulated by acquired immunity.
Assuntos
Desastres , Efeito Estufa , Helmintíase Animal/transmissão , Animais , Doenças das Aves/imunologia , Doenças das Aves/transmissão , Aves/imunologia , Aves/parasitologia , Helmintíase Animal/imunologia , Interações Hospedeiro-Parasita , Estágios do Ciclo de Vida , Dinâmica Populacional , Coelhos/imunologia , Coelhos/parasitologiaRESUMO
We present a detailed analysis of long-term time series of malaria incidence in northern Thailand. Positive cases for Plasmodium falciparum and P. vivax have been recorded monthly from 1977-2002 at 13 provinces in the region. Time series statistical methods are used to examine the long-term trends and seasonal dynamics of malaria incidence at regional and provincial scales. Both malarial types are declining throughout the region, except in the two provinces that share a large border with Myanmar. The rate of decline in P. vivax has decreased across the region since the end of the 1980s, and this may be a signal of developing resistance or changing vector potential. Both species display a two-peak annual seasonality that may be attributed to patterns of vector occurrence, farming practice and migration of individuals across international borders. In a number of provinces, the importance of the first seasonal peak has grown in recent years, possibly owing to increases in vector densities. The medium-term fluctuations of both species exhibit a clear spatial organisation. There is some evidence of a subtle close to 4-year super annual cycle in P. falciparum, which we suggest is driven by extrinsic factors relating to the climate of the region.
Assuntos
Malária Falciparum/epidemiologia , Malária Vivax/epidemiologia , Humanos , Incidência , Estações do Ano , Conglomerados Espaço-Temporais , Tailândia/epidemiologiaRESUMO
Insight into the dynamics of parasite-host relationships of higher vertebrates requires an understanding of two important features: the nature of transmission and the development of acquired immunity in the host. A dominant hypothesis proposes that acquired immunity develops with the cumulative exposure to infection, and consequently predicts a negative relationship between peak intensity of infection and host age at this peak. Although previous studies have found evidence to support this hypothesis through between-population comparisons, these results are confounded by spatial effects. In this study, we examined the dynamics of infection of the nematode Trichostrongylus retortaeformis within a natural population of rabbits sampled monthly for 26 years. The rabbit age structure was reconstructed using body mass as a proxy for age, and the host age-parasite intensity relationship was examined for each rabbit cohort born from February to August. The age-intensity curves exhibited a typical concave shape, and a significant negative relationship was found between peak intensity of infection and host age at this peak. Adult females showed a distinct periparturient rise in T. retortaeformis infection, with higher intensities in breeding adult females than adult males and non-breeding females. These findings are consistent with the hypothesis of an acquired immune response of the host to a parasite infection, supporting the principle that acquired immunity can be modelled using the cumulative exposure to infection. These findings also show that seasonality can be an important driver of host-parasite interactions.