Two genotypic groups of morphologically similar fish trypanosomes from the Okavango Delta, Botswana.

Blood smears and blood lysate samples from freshwater fishes captured in the Okavango Delta, Botswana, were examined to determine whether their trypanosomes were all Trypanosoma mukasai, a species of supposed broad host specificity and widespread existence across Africa. Trypanosomes and/or babesiosomes occurred in 20/32 blood smears, and morphometric analysis of trypanosomes from 13/32 smears showed features suggestive of T. mukasai, including nuclear indices consistently >1. In 16/32 blood lysate samples from which DNA was extracted, trypanosome DNA was detected in 12/16 by PCR (polymerase chain reaction), using trypanosome-specific ssu rRNA gene primers. Two samples positive for trypanosomes in blood smears yielded no amplifiable trypanosome DNA, but 4 samples with no detectable infection in blood smears were positive for trypanosome DNA, suggesting an overall trypanosome prevalence rate of 17/32 (53%) among fishes and demonstrating the value of PCR in trypanosome recognition. Cloning and sequencing of the 12 amplified fragments revealed 2 genotypic groups among these fish trypanosomes. Group 1 trypanosomes were from cichlids and 3 families of catfishes, Group 2 from 2 types of catfishes. Sequence comparison showed that the consensus Group 1 sequence was most similar to that of Trypanosoma cobitis, representing European fish trypanosomes of the carassii type, while the consensus Group 2 sequence showed similarity with a trypanosome sequence from another African catfish, Clarias angolensis. It was concluded that the identification of T. mukasai remains a problem, but at least 2 genotypic groups of trypanosomes occur in Okavango Delta fishes, and catfishes in this region appear to contain both types.