Galila M. Khalil

The Rift Valley fever epizootic in Egypt 1977–1978 2. Ecological and entomological studies

Epidemiological factors related to the introduction, spread and maintenance of Rift Valley fever (RVF) virus were studied during the 1977-78 epizootic in Egypt, Culex pipiens is the most ubiquitous and prevalent mosquito species in the Nile Valley and Delta. Isolation of RVF virus from unengorged C. pipiens, and demonstration of laboratory transmission of the virus by this species, strongly implicate it as the chief vector in Egypt. Virus transmission to man also occurs by contamination when handling infected meat and by inhaling natural virus aerosols. Wild rodents apparently do not serve as RVF virus reservoirs. Domestic sheep, cattle, buffaloes, camels, goats, donkeys and dogs act as amplifying hosts. Over 30% of the camels sampled at the southern border of Egypt were serologically positive for antibodies to RVF virus and it appears likely that the virus was introduced into Egypt, either by these animals or by other vehicles from the south.

HYPERPARASITISM IN ORNITHODOROS ERRATICUS

Hyperparasitism is common in laboratory colonies of Egyptian Ornithodoros erraticus whether the ticks are on or off the rodent host. Sex, recent engorgement, and size appear to be major factors in this feeding relationship. Males, and nymphs that produced males (N-male), parasitized females and nymphs that produced females (N-female) more frequently than they parasitized males and N-male. Females and N-female seldom parasitized females and N-female and did not parasitize males or N-male. Engorging and recently engorged, large ticks attracted smaller unfed ones. No preferred attachment site was observed. Hyperparasitizing females and parasitized females weighed less, had a longer preoviposition period, and produced fewer eggs than normally feeding, unparasitized females. About 30% and 80% of the females parasitized by males and females, respectively, died within 3 mo; only 7% of unparasitized females died within the same period. The proximity of replete or engorging ticks may be sufficient stimulus for hyperparasitism. Additional factors may include production of an attracting kairomone by fed ticks or the absence under certain conditions of a deterrent to hyperparasitism normally produced by fed ticks. Borrelia crocidurae spirochetes are transmitted during hyperparasitism.

Borrelia crocidurae: venereal transfer in Egyptian Ornithodoros erraticus ticks.

Abstract Male Ornithodoros (Pavlovskyella) erraticus infected with Borrelia crocidurae transferred the spirochetes to females during copulation. After the first and second gonotrophic cycles, spirochetes were observed in 23 and 37%, respectively, of the females. Venereal transfer by the polygamous male contributes significantly to supporting the B. crocidurae population in nature.

Biological evaluation of the systematic validity of the African Argas (Persicargas) Arboreus and the Asian-Australian A. (P.) Robertsi (Ixodoidea: Argasidae)

Abstract Khalil G. M. , Hoogstraal H. and Oliver J. H. Jr. 1980. Biological evaluation of the systematic validity of the African Argas (Persicargas) arboreus and the Asian-Australian A.(P.)robertsi (Ixodoidea: Argasidae). International journal for Parasitology 10 : 253–259. The closely related A. (P.) arboreus (Ethiopian Faunal Region) and A. (P.) robertsi (Oriental and Australian Faunal Regions) interbreed readily and produce partially fertile progeny. Intrahybrid crosses are much less productive than P 1 homogamic crosses. Results of backcrosses indicate that the progeny of the robertsi ♂ × arboreus ♀ cross are less fertile than the progeny of the reciprocal cross. The fertility of F 1 hybrid progeny is lower than that of the P 1 pure species as expressed in lower female fecundity, egg hatch, and/or viability of immature stages. These 2 species probably originated from a common ancestor and geographic isolation caused genetic incompatibility.

Hyalomma dromedarii (Acari: Ixodoidea: Ixodidae): Central and peripheral nervous system anatomy

TheHyalommadromedarii central nervous system, the synganglion, is an integrated nerve mass concentrated around the esophagus and formed by fusion of a small anterodorsal supraesophageal part an a large posteroventral subesophageal part. The supraesophageal part consists of the protocerebrum including a pair of optic ganglia, a pair of cheliceral ganglia, a pair of pedipalpal ganglia, and the stomodeal pons. The subesophageal part includes four paired pedal ganglia and the complex opisthosomatic ganglion. The peripheral nervous system includes the following pairs of nerves: optic, cheliceral, pedipalpal, primary and accessory (histologically traced); also unpaired pharyngeal and recurrent nerves, four pairs of pedal nerve trunks, each with a hemal branch, and two pairs of opisthosomatic nerves. Each peripheral nerve is traced distally to the innervation site. The salivary glands are innervated anteriorly by branches of the pedipalpal nerve and medially by branches of the hemal nerves associated with the third pedal nerves.

Effect of 20-hydroxyecdysone on neurosecretory cell activity in female Hyalomma dromedarii synganglion (Acari: Ixodidae)

Twentyμg of 20-hydroxyecdysone (20-he) were applied topically to nymphalHyalomma dromedarii Koch on the day of detachment. In emerging adult females, some neurosecretory cells (nsc) in certain synganglion centers exhibited changes in size and/or neurosecretory material (nsm) shape, distribution and/or quantity. These changes were compared with those normally occurring in untreated unfed, semifed virgin and mated, and engorged females. 20-he effects included (a) accelerating the changes induced by mating and/or feeding in certainnsc, (b) reducing, to various extents,nsc response to mating and feeding, and (c) inducing changes in somensc which do not normally exhibit any changes in untreated females. The results suggest that (a) most femalensc respond more or less similarly to indigenous 20-he, (b) 20-he may have a role as a positive feedback regulator fornsm synthesis and/or release by certainnsc, (c) the response to 20-he may be primarily a function ofnsc location in the synganglion, and/or (d)nsc considered to be of one type may actually belong to different cell types.

Nucleic Acid Levels in the Developing Ovaries of Hyalomma (Hyalomma) dromedarii (Acari: Ixodidae)

Protein and nucleic acid levels from the ovaries of Hyalomma dromedarii Koch were determined during different stages of oogenesis. The concentrations of total protein, DNA, and RNA increased during oogenesis, reflecting the rapid developmental changes taking place in this tissue. Peak protein and DNA levels were reached in the fully fed females, whereas RNA level peaked slightly earlier. Ribosomal RNA (rRNA) was found to be composed of 27.0s, 17.0s, and 4.1s particles. The ratio of 27.0s to 17.0s varied within the developing ovary, yet the 27.0s/4.1s ratio remained constant. The nucleotides of total RNA and rRNA were determined, and the ratio of purine/pyrimidine equaled approximately 1 and remained unchanged during oogenesis.

Biochemical Effects of Juvenile Hormone III on the Tick, Argas (Persicargas) arboreus (Acari: Argasidae), During Embryogenesis

The biochemical effects of juvenile hormone III (JH III) on developing embryos from treated female Argas (Persicargas) arboreus Kaiser, Hoogstraal and Kohls were examined. Exogenous JH III resulted in a decrease in total proteins (P less than 0.001) only during the first 2 d of embryogenesis. There was no significant difference (P greater than 0.05) between RNA and DNA content in eggs from control and JH III-treated females. No significant difference (P greater than 0.05) was observed between control and JH III eggs in their lipid or phospholipid contents throughout embryogenesis. A total of 14-17 protein bands and 6-8 glycoprotein bands were separated by electrophoresis during embryogenesis of A. arboreus with some differences in mobility ratio between bands from control and JH III eggs. Differences in activity and isozyme patterns of malic acid, lactic acid, glucose 6-phosphate dehydrogenase, acid phosphatase, and alkaline phosphatase were not observed during embryogenesis of control and JH III-treated A. arboreus. Differences were observed in esterase activity.