Epidemiology of Canine Leptospirosis in Kuala Lumpur and Selangor

This study was conducted to determine the current state of leptospirosis in dogs in Kuala Lumpur and Selangor. The usefulness of several laboratory techniques was also evaluated for the diagnosis of leptospires and determination of leptospirosis prevalence. One hundred and sixty five serum samples were collected and examined for serological prevalence of leptospirosis. The dogs surveyed were classified into stray and pet groups. Pet dog samples were obtained from dogs which were brought to the University Veterinary Hospital at Universiti Putra Malaysia (UVH-UPM). Samples from stray dogs were obtained from Society for the Prevention of Cruelty to Animals (SPCA), and Paws Animals Welfare Society (PAWS). All serum samples were screened for leptospiral IgM and IgO antibodies, using an enzymelinked immunosorbent assay (ELISA). Then, these serum samples were re-examined for leptospiral antibodies and serovar-specificity by the microscopic agglutination test (MAT). A serum sample was confirmed to have leptospiral infection if its MAT titre was 2: 100, or IgM-ELISA titres of 2: 160, or IgO-ELISA titres of more than two times of negative controls, or any combination of the above. The study showed a high serological prevalence of leptospiral infection, particularly in the group of stray dogs. Leptospira pomona was found to be the most predominant serovar both in the pet and stray dogs. In previous surveys in 1 95 5, 1 96 1 , 1 979 and 1 986, the infection due to L. pomona was uncommon whilst L. icterohaemorrhagiae and L. canicola were reported to be predominant in dog populations in Malaysia. The emergence of L. pomona infection in dogs in Malaysia could be due to the only use of vaccines containing serovars icterohaemorrhagiae and canicola. Therefore, to prevent leptospiral infection in dogs and reduce the transmission of this disease from dogs to other animals and humans, serovar pomona should be included in the vaccines to be used in Malaysia. The bacterial culture revealed no leptospires in the dogs surveyed. This could possibly be due to the fastidious nature of the organisms, stage of infection, or level of antibodies in the circulating blood. However, twenty one unknown isolates were successfully detected in blood and urine samples of the dogs surveyed by the polymerase chain reaction (PCR) and identified by low-stringency PCR technique

Influence of Gastric Acid on Susceptibility to Infection with Ingested Bacterial Pathogens▿

Despite the widely held belief that gastric acid serves as a barrier to bacterial pathogens, there are almost no experimental data to support this hypothesis. We have developed a mouse model to quantify the effectiveness of gastric acid in mediating resistance to infection with ingested bacteria. Mice that were constitutively hypochlorhydric due to a mutation in a gastric H+/K+-ATPase (proton pump) gene were infected with Yersinia enterocolitica, Salmonella enterica serovar Typhimurium, Citrobacter rodentium, or Clostridium perfringens cells or spores. Significantly greater numbers of Yersinia, Salmonella, and Citrobacter cells (P ≤ 0.006) and Clostridium spores (P = 0.02) survived in hypochlorhydric mice, resulting in reduced median infectious doses. Experiments involving intraperitoneal infection or infection of mice treated with antacids indicated that the increased sensitivity of hypochlorhydric mice to infection was entirely due to the absence of stomach acid. Apart from establishing the role of gastric acid in nonspecific immunity to ingested bacterial pathogens, our model provides an excellent system with which to investigate the effects of hypochlorhydria on susceptibility to infection and to evaluate the in vivo susceptibility to gastric acid of orally administered therapies, such as vaccines and probiotics

The NanI and NanJ Sialidases of Clostridium perfringens Are Not Essential for Virulence▿

The essential toxin in Clostridium perfringens-mediated gas gangrene or clostridial myonecrosis is alpha-toxin, although other toxins and extracellular enzymes may also be involved. In many bacterial pathogens extracellular sialidases are important virulence factors, and it has been suggested that sialidases may play a role in gas gangrene. C. perfringens strains have combinations of three different sialidase genes, two of which, nanI and nanJ, encode secreted sialidases. The nanI and nanJ genes were insertionally inactivated by homologous recombination in derivatives of sequenced strain 13 and were shown to encode two functional secreted sialidases, NanI and NanJ. Analysis of these derivatives showed that NanI was the major sialidase in this organism. Mutation of nanI resulted in loss of most of the secreted sialidase activity, and the residual activity was eliminated by subsequent mutation of the nanJ gene. Only a slight reduction in the total sialidase activity was observed in a nanJ mutant. Cytotoxicity assays using the B16 melanoma cell line showed that supernatants containing NanI or overexpressing NanJ enhanced alpha-toxin-mediated cytotoxicity. Finally, the ability of nanI, nanJ, and nanIJ mutants to cause disease was assessed in a mouse myonecrosis model. No attenuation of virulence was observed for any of these strains, providing evidence that neither the NanI sialidase nor the NanJ sialidase is essential for virulence