Brian Dwyer

Specific syphilis serological tests may become negative in HIV infection.

The diagnosis of syphilis is frequently dependent upon the results of serological tests, but the reliability of syphilis serology in patients with HIV-1 infection has been questioned. We examined specific antibody to Treponema pallidum (TP) using the TP haemagglutination (TPHA) and fluorescent treponemal antibody-absorption (FTA-ABS) tests in AIDS patients and HIV-antibody-negative controls with a history of syphilis. Tests were carried out on two sera separated by an interval of at least 3 years from each patient. Twelve out of 29 AIDS patients compared with four out of 29 controls showed significant falls in titres of specific antibody as measured by the TPHA, FTA-ABS, or by both the TPHA and FTA-ABS (P = 0.02). Furthermore, in three out of 29 (10%) of the AIDS patients with past syphilis infections both the TPHA and FTA-ABS became non-reactive. We conclude that negative specific serology does not exclude a past syphilis infection in patients with AIDS.

Genotype and phenotype of oral Candida albicans from patients infected with the human immunodeficiency virus.

Candida albicans has been shown to vary in its phenotypic expression with the progression of human immunodeficiency virus (HIV) infection. Isolates of C. albicans were obtained from 45 patients with HIV infection during the progression of their disease and differentiated using two methods. The first utilized the morphological characteristics of colonies, and the second method utilized a small portion of C. albicans DNA as a probe on Southern-transferred, EcoRI-digested C. albicans genomic DNA. In 67% of the patients a single strain of C. albicans, as determined by the DNA analysis, was isolated from each individual. The phenotypic expression of the genetically identical strains varied considerably over the experimental period with one morphotype being predominant. These results showed that the genotype of C. albicans persisted in the majority of HIV-infected individuals, but that the phenotypical expression of this strain changed. A novel finding in this study was that 18 strains of C. albicans had DNA which did not hybridize to the probe used.

Antibody response to campylobacter pylori in diverse ethnic groups

Antibody response to Campylobacter pylori was measured in ethnic groups of Vietnamese, El Salvadorean and Ethiopian origin. The results were compared with the previously reported antibody titres found in sera of culture positive and culture negative patients, patients suffering from duodenal ulcer, white Australian blood donors and Australian Aboriginals. While in Vietnamese the prevalence of serologically positive sera was found to be similar to the white Australian population, numbers of serologically positive sera in El Salvadorean and Ethiopian ethnic groups was found to be very high. The high incidence of serologically positive sera in the Ethiopians correlated with the reported high incidence of duodenal ulcer in this population.

Spotted fever group rickettsial infection in South-Eastern Australia: Isolation of rickettsiae

Flinders Island spotted fever (FISF), a spotted fever group (SFG) rickettsial disease first described in 1991, occurs in south-eastern Australia. The isolation of the aetiological agent is described for the first time having been obtained from the blood of two patients. An additional 22 cases are also reported. Of these patients four had positive initial serology, and 20 showed seroconversion (using Rickettsia australis as antigen). Acute phase blood specimens taken from seven patients caused neonatal mice to seroconvert to R. australis and a blood specimen from one of these patients (and one other) yielded rickettsiae. A field survey for possible reservoir and vector animals on Flinders Island, Tasmania and in Gippsland, Victoria (both in south-eastern Australia) yielded 217 vertebrates and 1445 invertebrate ectoparasites, mostly ticks. Ixodes cornuatus from humans and dogs in Gippsland produced seroconversion to SFG rickettsia when inoculated into mice but no invertebrate pools from Flinders Island produced seroconversion in mice. Haemolymph from an individual I. cornuatus removed from a human in Gippsland, yielded a SFG rickettsia on tissue culture. Sera from several species of native vertebrates, especially the bush rat, Rattus fuscipes, were positive for antibodies to SFG rickettsia.

Enzyme-linked immunosorbent assays for detecting antibody to Rickettsia australis in sera of various animal species

New endemic areas of spotted fever-like rickettsial disease have been found in south-eastern Australia (Gippsland, Victoria and Flinders Island, Tasmania). The rickettsia responsible is currently unknown although it may be Rickettsia australis. To investigate serological evidence of rickettsial exposure in various wild animal species, a competitive ELISA was developed which detected antibodies to R. australis. It was based on inhibition of an indirect ELISA detecting antibody to R. australis in guinea pig sera. Pre- and post-infection sera from 2 dogs, 2 rabbits, 5 mice and 6 rats, experimentally infected with R. australis, were tested by competitive ELISA. The results showed that all pre-infection sera were negative and all post-infection sera positive for antibody to R. australis. To test the utility of the competitive ELISA for detecting natural rickettsial infection in non-laboratory animals, 51 dog sera, negative for rickettsial antibody by immunofluorescence (IF) and 20 IF positive dog sera (collected from various locations on the east coast of Australia) were tested. Compared to the IF test the competitive ELISA was 90% sensitive and 96% specific. This new test has potential for detecting antibody to R. australis in the sera of different wild animal species.