Mario Ziller

Impact of the El Nino/Southern Oscillation on visceral leishmaniasis, Brazil

We used time-series analysis and linear regression to investigate the relationship between the annual Niño-3 index from 1980 to 1998 and the annual incidence of visceral leishmaniasis (VL) in the State of Bahia, Brazil, during 1985–1999. An increase in VL incidence was observed in the post-El Niño years 1989 (+38.7%) and 1995 (+33.5%). The regression model demonstrates that the previous year’s mean Niño-3 index and the temporal trend account for approximately 50% of the variance in the annual incidence of VL in Bahia. The model shows a robust agreement with the real data, as only the influence of El Niño on the cycle of VL was analyzed. The results suggest that this relationship could be used to predict high-risk years for VL and thus help reduce health impact in susceptible regions in Brazil.

A field study to control Echinococcus multilocularis -infections of the red fox ( Vulpes vulpes ) in an endemic focus

Foxes harbouring E. multilocularis represent an important source for human infection with this parasite which causes alveolar echinococcosis. To minimize the risk of human infection, a control study was conducted to reduce the prevalence of E. multilocularis-infection in foxes in an focal endemic area of 5000 km2. Foxes were given access to baits containing 50 mg praziquantel. Twenty baits per km2 were distributed by airplane during 14 campaigns. The effects of control measures were monitored by parasitological examination of 9387 foxes shot before and during the control trial. A distinct reduction of the prevalence of E. multilocularis was observed for both, the initially endemic area and the low-endemic periphery. The effect was more pronounced in adult than in juvenile foxes. Under control conditions, the risk area decreased in size. However, an eradication of the parasite was not reached with the chosen strategy.

Regional distribution of bovine Neospora caninum infection in the German state of Rhineland-Palatinate modelled by Logistic regression

To obtain a rapid overview over the distribution of bovine Neospora caninum-infections in the German state of Rhineland-Palatinate, an ELISA to determine specific bovine antibodies against a p38 surface antigen of N. caninum tachyzoites was modified to examine bulk milk samples from cattle herds. Experimental bulk milk samples were used to demonstrate that the seroprevalence in a group of animals can be estimated with this ELISA. A cut-off was selected for the specific detection of herds having a seroprevalence > or =10%. About 90% of the dairy herds located in Rhineland-Palatinate were examined. An overall prevalence of bulk milk-positive herds of 7.9% (95% confidence interval 7.0-8.9%), respectively, was determined. Major regional differences in the distribution of bulk milk-positive herds were observed. Prevalences were higher in regions with an increased degree of urbanisation. Logistic regression was applied to model the prevalence of bulk milk-positive herds on a district and city level. Variables describing the dog density, mean temperature in July, mean temperature in January and the total yearly precipitation in districts and cities were able to explain most of the observed variability in the regional prevalences. Our results provide evidence that in addition to risk factors related to individual farms also risk factors related to the farm location such as dog density in the surrounding and climate factors are important in the epidemiology of bovine neosporosis.

Trends in the temporal and spatial distribution of visceral and cutaneous leishmaniasis in the state of Bahia, Brazil, from 1985 to 1999

Temporal and spatial trends in the geographical distribution of 12,413 cases of American visceral leishmaniasis (AVL) and of 48,138 cases of American cutaneous leishmaniasis (ACL) notified from 1985 to 1999 in the State of Bahia, Brazil, were analysed. The emergence of new endemic municipalities indicated an increasing trend for AVL and ACL. In the years 1985, 1990 and 1996, AVL was endemic in 7% (n = 31), 18% (n = 73) and 30% (n = 123), and ACL was endemic in 13% (n = 54), 27% (n = 112) and 34% (n = 140), of 415 municipalities. New trends were identified, and the relation with the ecoepidemiology of both diseases is discussed.

A Bayesian model for spatial wildlife disease prevalence data

The analysis of the geographical distribution of disease on the scale of geographic areas such as administrative boundaries plays an important role in veterinary epidemiology. Prevalence estimates of wildlife population surveys are often based on regional count data generated by sampling animals shot by hunters. The observed disease rate per spatial unit is not an useful estimate of the underlying disease prevalence due to different sample sizes and spatial dependencies between neighbouring areas. Therefore, it is necessary to account for extra-sample variation and spatial correlations in the data to produce more accurate maps of disease incidence. The detection of spatial patterns is complicated by missing data in many of the geographical areas as the complete coverage of all areas is nearly impossible in wildlife surveys. For this purpose a hierarchical Bayesian model in which structured and unstructured over dispersion is modelled explicitly in terms of spatial and non-spatial components was implemented by Markov chain Monte Carlo methods. The model was empirically compared with the results of a non-spatial beta-binomial model using surveillance data of pseudorabies virus infections of European wild boars (Sus scrofa scrofa L.) in the Federal State of Brandenburg, Germany.

Bayesian space-time analysis of Echinococcus multilocularis-infections in foxes.

A total of 26,220 foxes that were hunted or found dead in Thuringia, Germany, between 1990 and 2009 were examined for infection with Echinococcus multilocularis, the causative agent of human alveolar echinococcosis, and 6853 animals were found infected. The available data on the foxes including the location (local community; district) and the date of hunting/death were analyzed using a hierarchical Bayesian space-time model. The distribution of the model parameters and their variability was estimated on the basis of the sample size, the number of cases per spatial unit and time interval, and an adjacency matrix of the municipalities using a Markov Chain Monte Carlo simulation technique to assess the spatial and temporal changes in the distribution of the parasite. The model used to evaluate the data is widely applicable and can be applied to analyse data sets with gaps and variable sample sizes per spatial and temporal unit. In the study area, the prevalence of E. multilocularis increased from 11.9% (95% confidence interval 9.9-14.0%) in 1990 to 42.0% (39.1-44.1%) in 2005. While the infection was present in foxes only in the north-western parts of Thuringia in 1990, it had spread over the entire state by 2004. These results demand increased vigilance for human alveolar echinococcosis in Thuringia.

Analysis of sampling strategies to substantiate freedom from disease in large areas

In this paper, we deal with the strategies of surveys to substantiate freedom from disease for a certain territory. Infection might not be distributed homogeneously. So, a relatively high within-herd prevalence might be observed while the herd-level prevalence is lower. For this situation, we compare various two-stage sample strategies. The calculation of appropriate sample sizes becomes quite complicated. The theoretical generalization of the hypergeometric distribution by Cameron and Baldock [Prev. Vet. Med. 24 (1998) 1] introduces a simple way to evaluate multi-stage sample sizes while regarding real-test properties. We demonstrate the theoretical foundations of these calculations. These principles open up the possibility of optimizing costs or other relevant variables, by choosing the appropriate sample strategy (each of which ensures the same alpha-level for the first stage). In addition, we evaluate the statistical power of the complete strategies under consideration.Furthermore, we apply our theoretical results to a data example of Brucella melitensis. We used the herd-size situation in Germany, characterized by many small sheep holdings and only a few large ones. The consequences of real-test properties on sample sizes and on the applicability of several strategies are discussed.

Serotyping of Toxoplasma gondii in Cats (Felis domesticus) Reveals Predominance of Type II Infections in Germany

Background Cats are definitive hosts of Toxoplasma gondii and play an essential role in the epidemiology of this parasite. The study aims at clarifying whether cats are able to develop specific antibodies against different clonal types of T. gondii and to determine by serotyping the T. gondii clonal types prevailing in cats as intermediate hosts in Germany. Methodology To establish a peptide-microarray serotyping test, we identified 24 suitable peptides using serological T. gondii positive (n=21) and negative cat sera (n=52). To determine the clonal type-specific antibody response of cats in Germany, 86 field sera from T. gondii seropositive naturally infected cats were tested. In addition, we analyzed the antibody response in cats experimentally infected with non-canonical T. gondii types (n=7). Findings Positive cat reference sera reacted predominantly with peptides harbouring amino acid sequences specific for the clonal T. gondii type the cats were infected with. When the array was applied to field sera from Germany, 98.8% (85/86) of naturally-infected cats recognized similar peptide patterns as T. gondii type II reference sera and showed the strongest reaction intensities with clonal type II-specific peptides. In addition, naturally infected cats recognized type II-specific peptides significantly more frequently than peptides of other type-specificities. Cats infected with non-canonical types showed the strongest reactivity with peptides presenting amino-acid sequences specific for both, type I and type III. Conclusions Cats are able to mount a clonal type-specific antibody response against T. gondii. Serotyping revealed for most seropositive field sera patterns resembling those observed after clonal type II-T. gondii infection. This finding is in accord with our previous results on the occurrence of T. gondii clonal types in oocysts shed by cats in Germany.

Seasonality in the proportions of domestic cats shedding Toxoplasma gondii or Hammondia hammondi oocysts is associated with climatic factors

A previous study on domestic cats in Germany and neighbouring countries suggested seasonality in shedding Toxoplasma gondii oocysts. The aim of the present study was to elucidate whether this seasonality in shedding could be explained by climatic effects and whether differences between years in the proportions of cats shedding oocysts could also be explained by climatic factors. To this end, a long-term study over a period of 55 months on domestic cats for T. gondii and Hammondia hammondi oocysts was performed and the results compared with climatic data. Using species-specific PCR, T. gondii oocysts were identified in 0.14% (84/61,224) and H. hammondi in 0.10% (61/61,224) of the samples. Toxoplasma gondii oocysts were predominantly observed from summer to autumn, while H. hammondi oocysts were mainly found during autumn and winter. In statistical analyses using climatic data, even differences in parasitological findings between years could be partially modelled using monthly temperature, North Atlantic Oscillation indices and precipitation. Of the three climatic variables analysed, precipitation as an explanatory variable had the lowest impact in the statistical models while those taking only temperature and North Atlantic Oscillation indices into account were sufficiently predictive. Interestingly, time lags between the climatic event and the parasitological findings had to be implemented in all models. For T. gondii, North Atlantic Oscillation indices with a time lag of 7 months and temperature with a time lag of 2 months had the best predictive value. In contrast, temperature (with a time lag of 6 months) and the interaction of precipitation (with a time lag of 5 months) and North Atlantic Oscillation indices (with a time lag of 11 months) were optimal for predicting the seasonality of H. hammondi. These results suggest prominent differences in the life cycles of the two closely related parasites. Previous findings showed that H. hammondi lack avian hosts, in contrast to T. gondii, and the coincidence in the periods of high abundance of birds and high proportions of cats shedding T. gondii suggest that birds may play an important role in the epidemiology of this infection. The result that North Atlantic Oscillation index is an important variable in modelling variations in the proportion of cats shedding T. gondii and H. hammondi over the year is an indication that global warming may also influence the infection risk of animals and humans with T. gondii and H. hammondi. The findings have important implications for planning epidemiological studies and for estimating the risk of human infection.