The trypanosome infections of Glossina pallidipes in the Umfolosi Game Reserve, Zululand

Abstract

Further dissections of Glossina pallidipes Aust., trapped in the Umfolosi Game Reserve in Zululand, were carried out between October 1932 and June 1933 and the results compared with those obtained between November 1931 and April 1932 [ R.A.E., B 21 107]. The percentage of trypanosome infection appeared to have increased from 3.42 in the first period to 5.14 in the second, and whereas in the former period 3.31 per cent. of the males and 3.46 of the females showed infections, in the latter the respective percentages were 6.87 and 4.45. A comparison between an area where intensive trapping was being carried out and one in which trapping had been abandoned and fly conditions were consequently returning to normal showed a fly density of 1.8 flies per trap per day in the first area and 60.2 in the second, a regularly higher percentage of infection in the latter, and differences in the distribution of the three species of trypanosomes ( Trypanosoma vivax, T. congolense and T. brucei). As these variations occurred in localities only about 5 miles apart, they appear to indicate that flies do not pass with any regularity from one focus to another. Proboscis infection in tsetse-fly in Zululand appears to occur throughout the year, but fluctuates in frequency from month to month. In 87 per cent. of the infected flies, the hypopharynx contained trypanosomes, and it is therefore assumed that the majority of the flies were capable of transmitting i them. With regard to the effect on the trypanosome infections of the reduction of fly population by trapping, the general results appear to show that as the population becomes less dense the percentage of infected flies increases, the increase occurring in the number of males infected. It is possible that this may be due to the greater attraction of the traps for females, the young females being removed more rapidly than the males, which therefore have a longer period in which to acquire infection. Out of 18 flies examined from an area of low fly density outside the Reserve, 4 were infected, and again more males were infected than females. Three of the flies were infected with T. congolense and one with T. brucei; it thus appears that the most pathogenic trypanosomes are being carried far from their source in the Game Reserve.

The author describes an anomaly in the structure of the salivary glands and hypopharynx occurring in 2.8 per cent. of the flies examined and discusses its possible bearing on the transmission of trypanosomes.

During an outbreak of trypanosomiasis of cattle in the winter of 1932, Stomoxys was present in large numbers in the locality and persistently attacked cattle, some of which were infected with T. congolense and T. brucei. Flies of this genus that fed on a donkey with numerous trypanosomes in its peripheral blood readily became infected. Trypanosomes ( T. congolense) remained active in the gut of Stomoxys for a maximum of 20 hours, and 8 per cent. of the Stomoxys interrupted while feeding on a donkey heavily infected with T. brucei showed trypanosomes in both gut and proboscis