The development of Dirofilaria immitis in the mosquito Aedes aegypti

1. The developmental stages of D. immitis in the mosquito A. aegypti at 26°C. have been followed in living and fixed preparations, and the fates of the cell groups of the microfilaria have been traced.

2. The larvae spend the first six or seven days inside the distal cells of the Malpighian tubules; during the next six days they inhabit the lumen of the tubules and eventually migrate to the head of the mosquito on the fifteenth to seventeenth day.

3. The “nuclear-column“ cells contribute largely to the formation of the oesophagus of the infective larva.

4. The G cells 1–3 produce the intestine and the G4 cell forms the anal plate and then the rectum.

5. The anal pore ultimately becomes the anus.

On two filarial parasites from dogs in Ceylon, Brugia ceylonensis n. sp. and Dipetalonema sp.inq

A new species of Brugia, from the lymphatic glands of dogs in Ceylon, is described. It is closely related to B. patei (Buckley, Nelson and Heisch, 1958).

Also from dogs in Ceylon, a species of Dipetalonema was recovered whose relationship with other species of Dipetalonema is discussed. In the absence of conclusive evidence that it is a distinct species it is for the present regarded as a species inquirenda.

The behaviour and development of Brugia patei (Buckley, Nelson and Heisch, 1958) in a mosquito host, Mansonia uniformis (Theobald)

1. The behaviour and development of Brugia patei has been followed in the mosquito host, Mansonia uniformis, from ingestion of the microfilariae to the development of the infective stages.

2. The microfilariae penetrated very rapidly out of the stomach into the abdomen of the mosquito; 80% of them escape from the stomach during the first 50 minutes after a blood meal.

3. The microfilariae migrate from the abdomen to the thorax through fat body cells and the heart during the first 140 minutes followed engorgement and begin to penetrate the indirect flight muscles within 15 minutes from engorgement. During this migration microfilariae were found in close association, suggesting that they follow similar pathways of migration through the body of the mosquito.

4. Most microfilariae (98%) have settled in the indirect flight muscles within 2 hours of engorgement. In these muscles the larvae digest away the muscle surrounding them but do not begin to elongate until the third or fourth day after the blood meal. The rate of development varies from one mosquito host to another, but about 80% of the larvae have developed to the infective stage by the ninth to tenth days after the infective feed. The infective stages concentrate in the head and proboscis of the mosquito vector. The development of B. patei is faster than that of B. pahangi in mosquitoes from the same colony.

5. The efficiency of M. uniformis as a vector of B. patei is compared with the similar efficiency of M. longipalpis as a vector of B. malayi. In both mosquitoes the majority of the microfilariae ingested develop to the infective stage. M. uniforms is also an efficient vector of B. pahangi.

6. The development of the parasite is discussed briefly with reference to knowledge of the physiological events within the mosquito host subsequent to the blood meal.

On a new species of Icosiella Seurat, 1917 from Malaya with a key to the species of Icosiella

A number of filariid worms were obtained from the connective tissues of the muscles of two Malayan amphibians. These include 22 males and 40 females from Bufo asper Boulenger from Taiping, Perak; 2 males and 2 females from Bufo asper, from Gunong Pulai, Johore; and 1 male and 4 females from Rana cancrivora, Gravenhorst from Thomson Road, Singapore. On examination these were found to be a new species of Icosiella for which the name Icosiella innominata sp. nov. is now proposed. A tentative key has also been drawn up for the species of the genus.

The identification of infective filarial larvae in Simuliidae

Although it is recognized that the presence of animal filariae can lead to confusion in the interpretation of infection rates in mosquito vectors of filariasis, the filariae found in man-biting simuliids are usually assumed to be Onchocerca volvulus. The authors of this paper emphasize that it is unwise to calculate transmission indices from infection rates in man-biting simuliids unless there is confidence in the identification of the filarial larvae. In this respect they cite their observations on Mount Elgon in Uganda which show that the majority of the filarial larvae in Simulium neavei-the local vector of onchocerciasis-are of species that do not affect man.To assist in the correct interpretation of infection rates in the vectors the authors made a detailed study of the morphological character of O. volvulus infective larvae and established criteria for distinguishing O. volvulus from other filariae known to be transmitted by simuliids.