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Infection of Culicoides variipennis, Culicoides nubeculosus, Culicoides riethi and Aedes aegypti with Mansonella ozzardi
CORRESPONDENCE Infection of Culicoides variipennis, Culicoides nubeculosus, Culicoides riethi and Aedes aegypti with Mansonella ozzardi SIR-I have recently carried out a short series of experiments to infect three species of Culicoides and one species of mosquito with the microfilariae of Mansonella ozzardi. Batches of midges totalling 413 C. variipennis and 53 C. nubeculosus were fed through membranes of oneday-old chick-skin on suspensions of Mansonella ozzardi microfilariae in human blood (650 mf/mm3). Infected blood had been obtained from a patient in Trinidad, stored for 24 hours under sterile conditions at 4°C while being transported to London and was offered to the midges on three successivedays. Several females from the first batch of fed C. variipennis were dissected immediately after engorgement to determine whether microfilariae had been ingested. Five specimens (12.5%) were found to contain microfilariae in the blood meal. Surviving midges were dissected eight days after the final batch had been fed. In dissection midges were placed on a cavity slide and teased in a drop of Medium 199 (Flow Laboratories Ltd). A total of 22 infective stage filarial larvae were recovered from C. variipennis; most of the infected midges were in the batch fed upon four-day-old blood. Another three infective stage larvae were recovered from 17 C. nubeculosus eight days after their infection. Infective stage larvae were pooled and inoculated subcutaneously into a male jird (Meriones unguiculatus). No developing or adult worms were found when this animal was dissected five months later. Several other jirds at the London School of Hygiene and Tropical Medicine had also been inoculated with infective larvae, from C. phlebotomus, a natural vector of M. ozzardi. These animals also apparently failed to support the development of adult worms (MULLER, personal communication). In a second experiment, carried out concurrently with the membrane feeding trials, 100 C. variipennis, 50 C. nubeculosus, 50 C. riethi and 50 Aedes aegypti were inoculated intrathoracically with the blood containing microfilariae of M. ozzardi. Unfortunately, the inoculum proved to be rather toxic and all the inoculated midges and mosquitoes died within seven days of inoculation. Normally the mortality of inoculated insects is only 20% greater than for uninoculated specimens when employing this technique for inoculating insects with arboviruses suspended in buffered salt solutions (BOORMAN, 1975). Several apparently normal first-stage (sausage) larvae were recovered from moribund inoculated C. variipennis, C. nubeculosus and C. riethi. Also a total of 15 sausage-stage and two second-stage larvae were recovered from 20 moribund Ae. aegypti when dissected between four and seven days after inoculation after incubation at 26°C. Larval development in Ae. aegypti is surprising as these mosquitoes have not been implicated in the transmission of M. ozzardi. When further supplies of M. ozzardi microfilariae are available it would be interesting to suspend them in P.B.S. (phosphate buffered saline), rather than blood, for inoculation into Ae. aegypti. P.B.S. is not toxic to insects and would allow the possibility of larval development to be studied throughout a more natural duration. Bypassing the gut and the so-called “gut barrier” in this manner might enable larval development of M. ozzardi to
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proceed in this abnormal insect host which is so amenable to colonization and experimentation in the laboratory. I am, etc., P. S. MELLOR Animal Virus Research Institute, Pirbright, Surrey, England
Reference Boorman, J., 1975. Semi-automatic device for inoculation of small insects with viruses. Laboratory Practice, 24, 90. Hydatid disease among the Dassanetch of southwest Ethiopia Sn-Hydatid disease, which affects man and his domestic animals, is known to be very common in parts of southern Sudan and northern Kenya (WRAY, 1958; NELSONet al, 1963; CAHILL et al, 1965; MANN, 1974). Although the disease is reported in many other parts of Africa, this region has been particularly noted for its high prevalence (MANN, 1974). The boundary for this area of high prevalence for hydatid disease in man can now be extended into a large area of southwest Ethiopia. Although previously no areas of Ethiopia have been noted for a particularly high prevalence of hydatid disease in the human population, it has been reported to occur “time and again” in all parts of the country (SCHALLERand KULS, 1972). We have recently found it to be extremely common clinically in at least three population groups in the southern part of Ethiopia. In order to get some idea of the possible prevalence of the disease, physical examination and the Casoni skin test were utilized. The antigen was taken directly from sheep hydatids at the University of California at Davis. Although the antigen is not purified and both false negatives and positives occur not infrequently with the test (BRAND, 1965; KAGAN et al, 1966; CHERUBIN,1969), it should give at least a rough idea of the prevalence (LASS and NITZANI, 1956; LUPASCOet al, 1967). Clinically the disease appeared to be common among the Dassanetch (Geleb), Nyangatom (Bume) and Kerre people, as well as being at least present among the Hamar people. In these groups, 640 individuals were examined for abdominal masses.As appropriate diagnostic facilities were not available, little attempt was made to detect lung cysts which in many clinical series may account for well over 30% of cysts in human hydatid disease (FOSTER, 1958; RAKOWER, 1960; RAMIREZ, 1971). Among 158 Dassanetch, 11.3 % had a readily palpable, resonant cyst, multiple cysts, or highly suggestive liver masses. This compares to 5.8% among 155 Nyangatom, 5% among 20 Kerre, only 1.6 % among 152 Hamar and none among 155 Suri. All groups in the area possess sheep, goats, cattle and dogs in varying quantities. Unlike the Turkana, none of these groups make much use of camels, the potential importance of which has been suggested by the work of MOBEDI et al (1970) in Iran. In this initial survey, 175 people, the majority of whom were Dassanetch from the Eleli clan, were skin tested. The Dassanetch subjects were not selected on the basis of clinical signs. Sufficient antigen, 0.1-0.12 cc, was injected intradermally to raise a wheal of O&1.0 cm diameter and the reaction was read at 20-30 minutes. A wheal measuring at least 24 mm in one direction or 22 mm or greater in both directions was considered to be a positive
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proceed in this abnormal insect host which is so amenable to colonization and experimentation in the laboratory. I am, etc., P. S. MELLOR Animal Virus Research Institute, Pirbright, Surrey, England
Reference Boorman, J., 1975. Semi-automatic device for inoculation of small insects with viruses. Laboratory Practice, 24, 90. Hydatid disease among the Dassanetch of southwest Ethiopia Sn-Hydatid disease, which affects man and his domestic animals, is known to be very common in parts of southern Sudan and northern Kenya (WRAY, 1958; NELSONet al, 1963; CAHILL et al, 1965; MANN, 1974). Although the disease is reported in many other parts of Africa, this region has been particularly noted for its high prevalence (MANN, 1974). The boundary for this area of high prevalence for hydatid disease in man can now be extended into a large area of southwest Ethiopia. Although previously no areas of Ethiopia have been noted for a particularly high prevalence of hydatid disease in the human population, it has been reported to occur “time and again” in all parts of the country (SCHALLERand KULS, 1972). We have recently found it to be extremely common clinically in at least three population groups in the southern part of Ethiopia. In order to get some idea of the possible prevalence of the disease, physical examination and the Casoni skin test were utilized. The antigen was taken directly from sheep hydatids at the University of California at Davis. Although the antigen is not purified and both false negatives and positives occur not infrequently with the test (BRAND, 1965; KAGAN et al, 1966; CHERUBIN,1969), it should give at least a rough idea of the prevalence (LASS and NITZANI, 1956; LUPASCOet al, 1967). Clinically the disease appeared to be common among the Dassanetch (Geleb), Nyangatom (Bume) and Kerre people, as well as being at least present among the Hamar people. In these groups, 640 individuals were examined for abdominal masses.As appropriate diagnostic facilities were not available, little attempt was made to detect lung cysts which in many clinical series may account for well over 30% of cysts in human hydatid disease (FOSTER, 1958; RAKOWER, 1960; RAMIREZ, 1971). Among 158 Dassanetch, 11.3 % had a readily palpable, resonant cyst, multiple cysts, or highly suggestive liver masses. This compares to 5.8% among 155 Nyangatom, 5% among 20 Kerre, only 1.6 % among 152 Hamar and none among 155 Suri. All groups in the area possess sheep, goats, cattle and dogs in varying quantities. Unlike the Turkana, none of these groups make much use of camels, the potential importance of which has been suggested by the work of MOBEDI et al (1970) in Iran. In this initial survey, 175 people, the majority of whom were Dassanetch from the Eleli clan, were skin tested. The Dassanetch subjects were not selected on the basis of clinical signs. Sufficient antigen, 0.1-0.12 cc, was injected intradermally to raise a wheal of O&1.0 cm diameter and the reaction was read at 20-30 minutes. A wheal measuring at least 24 mm in one direction or 22 mm or greater in both directions was considered to be a positive