Impact of rapid urbanization on mosquitoes and their disease transmission potential in Accra and Tema, Ghana.

The total of 75 mosquito species recorded in Accra have declined to 28 species. Contributing factors to this decline and the reduction in prevalence of malaria and bancroftian filariasis in Accra presently include extensive water pollution and a fairly high daily mosquito mortality due to several factors including loss of natural adult resting places, use of mosquito repellents and the probable increase of Anopheles arabiensis population. Presently low yellow fever incidence is due inter alia to loss of its feral vectors and reduced intradomiciliary breeding of Aedes aegypti (L) although more common species like A. gambiae s.l., A. aegypti and C. p. quinquefasciatus could between them transmit many other arboviruses. However because of ready availability of human blood, spill-over of viruses from reservoir hosts to man will be rare. Ipso factor, malaria is the most common mosquito-borne disease with centripetal distribution of prevalence.

Diagnostic laboratory parasitology--a stepping stone to medical research in tropical Africa.

African countries can concentrate mainly on operational and problem-solving type of medical research using as a basis routine diagnostic laboratory parasitology which can be elevated to research level by incorporating all relevant techniques backed by statistically-based programming. Because of high incidence of parasitic infections and the peculiar host-parasite relationship, co-operation between all departments of any major hospital will be required to deal with the diseases due to them. Longitudinal studies on some parasites will enable generalisation and specific views to be formed on some infections. Multiplicity and wide variety of available techniques offer several research possibilities of clinico-pathological and epidemiological significance. Routine laboratory-based research offers the right environment for training various types of laboratory workers from technicians to medical parasitologists, through on-the-job training on techniques, investigative studies and research, backed by formal lectures and practicals at various levels. Trainee medical parasitologists can obtain higher degrees locally or abroad. The research can be organised around micro and mini research units. This approach is cost-beneficial because it minimises administrative difficulties and so avoids wastage. The results can be used to monitor impact of national development on parasitic infection prevalence and to formulate a policy on parasitic disease management.

Variation in frequency in breeding of Anopheles gambiae s.l. and its relationship with in-door adult mosquito density in various localities in Accra, Ghana.

The work reported in this paper was undertaken to determine whether in a large urban area like Accra, emerging Anopheles gambiae s.l. adults are likely to invade the nearest houses to obtain a blood meal. Using data from previous studies, the frequency in breeding was compared with adult density graphically and by scatter diagrams. Graphically, frequency in breeding was associated with adult density in eight districts while on the geometric scatter plot, these parameters were associated in ten districts. The finding of association of low frequency in breeding with moderate adult density in only one district and a correlation coefficient significant at p less than 0.001 on 14 degrees of freedom for 8 districts indicates that in the majority of districts, most adult mosquitoes invaded the nearest human habitation.

Effects of ecological changes on the malaria vectors Anopheles funestus and the Anopheles gambiae complex of mosquitoes in Accra, Ghana.

Studies have been conducted on mosquito breeding, indoor resting density and some parasitological and vectorial indices in Accra since 1911. An. gambiae s.l. has adapted to breeding appreciably in water-filled domestic containers in recent times (viz. 21.14 +/- 4.4% of all breeding), compared with a low frequency of breeding in such domestic containers in the earlier years 1911-1930 (viz. 1.97 +/- 1.67% of all breeding). Its breeding has also increased (viz. 5.3% to 25.4% of all breeding) in the numerous polluted water habitats created as a result of urbanization. This more widespread breeding in Accra city gave rise to only reduced indoor-resting densities of An. gambiae s.l. Several factors may be responsible for these changes, including the possible replacement of An. gambiae s.s. by the more versatile An. arabiensis as the predominant species in Accra. The almost complete elimination of An. funestus and decrease in breeding intensity of An. gambiae s.l. over the years have contributed to diminishing malaria parasite rates between 1912 and 1964 and may also account for low incidence of W. bancrofti infection in Accra in recent times.

Observation on the saliva and salivary gland extract of Haemaphysalis spinigera and Rhipicephalus sanguineus sanguineus.

Intracutaneous injection of histamine acid phosphate (HAP) and salivary gland extract (SGE) of Haemaphysalis spinigera and Rhipicephalus sanguineus sanguineus into sensitized and nonsensitized rabbits previously injected intravenously with Evans blue indicated that the ticks' saliva contained a pharmacodynamic substance in addition to having antigenic properties. A primary skin reaction in nonsensitized rabbits produced by this pharmacodynamic substance within 30 min was amplified by a more extensive skin reaction in sensitized rabbits. It was postulated that, in concert with this pharmacodynamic component of the ticks' saliva, a histamine-blocking agent detected in the salivary gland of R. s. sanguineus would provide an efficient mechanism for regulating the quantity of tissue fluid available for the engorging tick, while simultaneously neutralizing the deleterious effects of excess pharmacodynamic substance in the host's tissues.