AN INTERFERON GAMMA RELEASE ASSAY FOR THE DETECTION OF IMMUNE SENSITIZATION TO MYCOBACTERIUM BOVIS IN AFRICAN WILD DOGS (LYCAON PICTUS).

In South Africa, the largest proportion of the African wild dog (Lycaon pictus) population resides in regions where buffaloes have a high prevalence of Mycobacterium bovis, the causative agent of bovine tuberculosis (bTB). Recent reports of deaths of wild dogs associated with bTB have raised concerns regarding the threat this disease might pose for this species. In order to understand the potential impact of the disease in wild dogs, diagnostic tools are required to identify infected individuals. The interferon gamma (IFN-γ) release assay (IGRA) is commonly used for tuberculosis (TB) screening of humans, cattle, and other species, and the aim of this study was to develop an IGRA for wild dogs to detect immune sensitization. Blood was collected from immobilized wild dogs from the Ann van Dyk Cheetah Centre (AvDCC; n=9) and Kruger National Park (KNP; n=31). Heparinized whole blood was incubated overnight in QuantiFERON®-TB Gold (QFT) blood collection tubes and with selected mitogens, after which the plasma fraction was harvested. Three canine IFN-γ enzymelinked immunosorbent assays (ELISAs) were compared for detection of wild dog IFN-γ in plasma and the R&D Quantikine canine IFN-γ ELISA was selected for measurement of M. bovis-specific IFN-γ release in plasma samples. An IGRA result was calculated as the concentration in plasma derived from the QFT TB Antigen tubes minus that in the QFT Nil tube. An IGRA cut-off value was calculated using the IGRA results of M. bovis-unexposed individuals from AvDCC. Using this cut-off value, 74% (23/31) of M. bovis-exposed KNP wild dogs were IGRA positive, indicating immune sensitization to TB antigens in these animals. Three M. bovis culture-positive wild dogs from KNP had IFN-γ concentrations between 758 and 1,445 pg/mL, supporting this interpretation. This warrants further investigation into the prevalence of M. bovis infection in the KNP population.

PERFORMANCE OF THE TUBERCULIN SKIN TEST IN MYCOBACTERIUM BOVIS-EXPOSED AND -UNEXPOSED AFRICAN LIONS (PANTHERA LEO).

Lion (Panthera leo) populations, classified as vulnerable under the International Union for Conservation of Nature red list of threatened species, are facing a variety of threats, including tuberculosis (TB) caused by Mycobacterium bovis. The lack of knowledge on pathogenesis and diagnosis of TB, the prolonged course of the disease, the existence of subclinical infection, and nonspecific clinical signs hamper management of TB in both free-ranging and captive lion populations. Early and accurate antemortem diagnosis of M. bovis infections is important for disease management. In this study, we investigate the suitability of the single intradermal cervical test (SICT), developed with free-ranging Kruger National Park (KNP) lions exposed to M. bovis, for use in other lion populations. Using the recommended interpretation, the specificity of the SICT was low in disease-free captive lions, leading to false-positive diagnoses in 54% of individuals in the present study. Alternative interpretations of the tuberculin skin test are proposed that significantly reduce false-positive diagnosis in the sampled captive lions without significantly affecting diagnoses in the KNP lions; these changes may facilitate screening for M. bovis infection regardless of the exposure status of the lion population being investigated.

Promoter variation in the DC-SIGN-encoding gene CD209 is associated with tuberculosis.

BACKGROUND: Tuberculosis, which is caused by Mycobacterium tuberculosis, remains one of the leading causes of mortality worldwide. The C-type lectin DC-SIGN is known to be the major M. tuberculosis receptor on human dendritic cells. We reasoned that if DC-SIGN interacts with M. tuberculosis, as well as with other pathogens, variation in this gene might have a broad range of influence in the pathogenesis of a number of infectious diseases, including tuberculosis. METHODS AND FINDINGS: We tested whether polymorphisms in CD209, the gene encoding DC-SIGN, are associated with susceptibility to tuberculosis through sequencing and genotyping analyses in a South African cohort. After exclusion of significant population stratification in our cohort, we observed an association between two CD209 promoter variants (-871G and -336A) and decreased risk of developing tuberculosis. By looking at the geographical distribution of these variants, we observed that their allelic combination is mainly confined to Eurasian populations. CONCLUSIONS: Our observations suggest that the two -871G and -336A variants confer protection against tuberculosis. In addition, the geographic distribution of these two alleles, together with their phylogenetic status, suggest that they may have increased in frequency in non-African populations as a result of host genetic adaptation to a longer history of exposure to tuberculosis. Further characterization of the biological consequences of DC-SIGN variation in tuberculosis will be crucial to better appreciate the role of this lectin in interactions between the host immune system and the tubercle bacillus as well as other pathogens.