Massive infections of the tip of the proboscis with a minute rodlike or coccoid organism have been found in both males and females of three species of Phlebotomus from the Peruvian verruga zone. Over 300 such infections have been observed. The proportion of sandflies infected is frequently as high as 40 or 50 per cent. In many cases the pharynx is also infected.
The character of the proboscis infection as to microscopic appearance, intensity and distribution on the mouth-parts, is remarkably constant and apparently bears no relation to species, sex, age, or the presence or absence of a blood meal.
Out of about 300 uncontaminated cultures of the proboscis, B. bacilliformis has been recovered twice and an unnamed microorganism of similar morphology, about thirty times. There is some difficulty in the primary culture of the proboscis organisms, since about half the uncontaminated cultures from proboscides seen to be infected, yield no growth whatsoever. The unnamed microorganism probably accounts for the majority of the proboscis infections. Artificial feeding of P. verrucarum with cultures of B. bacilliformis has failed to produced comparable infections of the proboscis, while feeding cultures of the unnamed organism gave only one typical infection in a number of trials, although infections of the pharynx nearly always resulted. The data are thus far insufficient to make clear the extent to which Bartonella enters into these infections, and whether or not they represent the mechanism of transmission of Carrión's disease.
The source of the proboscis infections is unknown. Its occurrence in males, which do not suck blood, and in females which have never had a blood meal, indicates that the infection is probably acquired when sandflies seek other sources of liquids.