Genetic substructure in South African Bantu-speakers: evidence from autosomal DNA and Y-chromosome studies.

The extent of genetic differentiation between seven South African Bantu-speaking groups (Zulu, Xhosa, Tsonga/Shangaan, Southern Sotho, Pedi, Tswana, and Venda) was assessed from coancestry coefficients (F(ST)) estimated from autosomal serogenetic, DNA, and Y-chromosome DNA haplotypes. The overall F(ST) obtained from the autosomal data was 0.002, and that from the Y chromosome data was 0.014. The genetic relationships between groups examined were inferred from their cluster affinities in phylogenetic trees constructed from the genetic distances between them. Both autosomal and Y-chromosome DNA studies reveal that 6 of the 7 South African Bantu-speaking groups cluster according to their linguistic groupings, the exception being the Tsonga, who do not cluster with other Nguni language speakers, but rather with the Venda who live close to them. This suggests that the invading Shangaan-speakers, whose Nguni language was adopted by the Tsonga, did not have a major effect on the Tsonga gene pool, and that gene flow from the Venda into the Tsonga may have been considerable. Genetic distances were found to correlate with geographic distances between the regions where each group's apparent population density is the highest. Linguistic distances were also found to correlate with genetic distances, but linguistic and geographic distances showed no correlation. Together, these results suggest that linguistic and some genetic differentiation took place before the groups (or their forerunners) reached their present-day locations, and that further genetic change occurred after their arrival.

An evaluation of two indirect fluorescent antibody tests for the diagnosis of Legionnaire's disease in South Africa.

The specificity and sensitivity of the indirect fluorescent antibody test (IFA) for the diagnosis of Legionnaires' disease in South African patients is unknown. Heat-treated and formalin-treated antigen preparations from 456 normal blood transfusion donors and from 34 confirmed patients with the disease (3 culture-positive cases and 31 cases of seroconversion) were assessed. Tests using both antigens showed a relatively high degree of positivity at low titres in normal individuals with an age-related increasing frequency of positive tests. The best combinations of specificity and sensitivity of the heat-treated antigen determinations were at titres of 1/128 and for formalin-treated antigen at titres of 1/8 for both IgG and IgM. An IgM titre of 1/8 using the formalin-treated antigen appeared to be the best diagnostic criterion of the IFA but an antibody level of 1/8 using this antigen was attained in only 37.1% of cases on initial testing but 100% of cases on subsequent testing.