Dogs L. infantum infection from an endemic region of the north of Tunisia: a prospective study.

A follow-up study of 917 dogs was undertaken between 1994 and 1995 in the focus of visceral leishmaniasis in northern Tunisia. It permitted to assess the demography of the dog population, the importance of canine leishmaniasis (CL) and the determinants of seropositivity and mortality of dogs. Canine population was stable through time with an input of 231 dogs and an output of 218 dogs per year. The prevalence of seropositivity was 18% and 22.3% in 1994 and 1995 respectively and 90% of dogs were asymptomatic. Among 525 negative dogs in 1994 and reassessed in 1995, 78 seroconverted revealing an annual cumulative incidence of 14.74%. On the other hand, 23.47% (27/115) of seropositive dogs became negative in 1995. Age, presence of symptoms and density of dogs were independently associated with CL seropositivity. These results demonstrate the difficulty of control strategies of visceral leishmaniasis targeting the dog population.

Leishmania major infection in the fat sand rat Psammomys obesus in Tunisia: interaction of host and parasite populations.

The causative agent of cutaneous leishmaniasis, Leishmania major, was studied in a Tunisian population of the fat sand rat, Psammomys obesus. Seasonal changes in the abundances of parasite and host were monitored in a longitudinal field survey lasting 21 months. Overall, 566 P. obesus, collected during 10 trapping sessions between May 1995 and January 1997, were examined. Analysis of prevalence, using logistic regression, revealed that extrinsic factors, such as season and climatic conditions, and intrinsic factors, such as host age, have a combined effect. Leishmania major showed a seasonal pattern, with most transmission occurring in late summer and in autumn, when prevalences were 7.5- and 6.6-fold higher, respectively, than in spring. Prevalence peaked, at 70%, in September 1995 and then decreased to 0% in June 1996. The same temporal fluctuation was observed during the second study year, albeit among prevalences that were relatively low because of unusually dry conditions. Prevalence was highly dependent on the age of the P. obesus, and season and age acted in synergy so that the rodents were highly infected in late summer and in autumn. Prevalence was not correlated with the relative density of the P. obesus and also appeared independent of gender. Although the ear lesions observed on 378 sand rats during a 1-year survey were closely associated with Leishmania infection, such lesions were not good predictors of infection, as 35% of the rodents found to be infected had no visible lesions on their ears. The prevalences of Leishmania infection observed in this study, among P. obesus living in monospecific colonies, were generally lower than those observed in other studies of P. obesus. It seems possible that P. obesus living in monospecific colonies could have a lesser role in propagating the parasite than those living in plurispecific colonies of rodents, and act as an 'epidemiological sink'.

Patterns of the tapeworm Raillietina trapezoides infection in the fat sand rat Psammomys obesus in Tunisia: season, climatic conditions, host age and crowding effects.

The tapeworm Raillietina trapezoides was studied in a Tunisian population of the fat sand rat Psammomys obesus. Seasonal changes in the abundance of parasite and host were monitored in a longitudinal field survey lasting 20 months. In total 582 intestinal samples were collected during 10 trapping sessions between May 1995 and January 1997 and examined. The impact of abiotic and biotic factors on the prevalence and parasite burden were explored, using generalized linear models. R. trapezoides showed a seasonal pattern with most transmission occurring in summer and autumn. In August-September when the rodents were at low density and most adult (90-100%) were infected. In winter, infections with R. trapezoides were highly prevalent in the cohort of adults only. The worm burden by number was also high in late summer and autumn. Prevalence and parasite burden by number or by biomass were highly age dependent. Season and age act in synergy so that the rodents were highly infected in late summer and autumn. Unusually dry conditions in winter seemed to increase prevalence and to reduce the number of worms. There was no difference between males and females in prevalence or parasite burden (by number or by biomass). Prevalence was not correlated with the relative density of the hosts whereas parasite burden depended upon their densities. The more numerous the worms were, the smaller they were individually, reflecting a crowding effect. The possibility of an immune response regulating P. obesus is discussed, in regard to the very high natural prevalence and the variation in worm burden, and compared with other parasite-host systems.

Patterns of infection of haemoparasites in the fat sand rat, Psammomys obesus, in Tunisia, and effect on the host.

Two bacterial and one protozoan blood parasite, belonging to the genera Bartonella, Borrelia and Babesia, were studied in a Tunisian population of Psammomys obesus. Seasonal changes in the abundance of the parasites and host were monitored in a longitudinal field survey lasting 17 months. Blood samples collected during eight rodent-trapping sessions, between September 1995 and January 1997, were examined microscopically. Bartonella sp. showed a seasonal pattern, with most transmission occurring in summer and autumn; most rodents (90%) were infected in August-September, when they were at low density and adult. Borrelia sp. showed low prevalences, with few seasonal fluctuations, and Babesia sp. showed an intermediate pattern, differing from one year to another. In the cohort of adult rats, infections with Bartonella sp. and Babesia sp. were less prevalent in winter than in the previous summer. Single and mixed infections were equally prevalent in females and males, and in sexually active and inactive adults. In addition, infection had no apparent effect on the weight of adult P. obesus. The observation that the proportion of erythrocytes infected with Bartonella sp. decreased with increasing host age is probably indicative of some acquired immunity to this micro-organism. The absence of detectable infections with Borrelia sp. in old rats indicates that the prevalence and/or intensity of infection declines with host age or that infected animals die selectively. However, there was no indication that any of these parasites combined sufficient pathogenicity and abundance to have any measurable effect on the rodent population.

[Seroepidemiological survey of influenza and infectious anemia in Equidae in northeastern Tunisia]. / Enquête séroépidémiologique sur la grippe et l'anémie infectieuse des equidés dans le nord-est tunisien.

Using the haemagglutination inhibition and immunodiffusion tests, a national serological survey was carried out to detect antibodies to equine influenza (EI) (A/equi/1/Prague 56 and A/equi/2/Miami 63) and equine infectious anaemia (EIA) in horse sera collected in northeastern Tunisia. 533 samples were analysed for EIA antibodies. All were negative. 13.6% of 433 equine sera tested for EI antibodies were positive. These results are discussed and compared with others obtained in Tunisia and bordering countries.