Observations on the carrier state and related antibody titres during an outbreak of foot-and-mouth disease

An outbreak of foot-and-mouth disease in a partially immune population of cattle in Botswana is described. The results show that when cattle immunized by vaccination were presented with natural field challenge of FMD, many animals with immunity sufficient to protect them against clinical disease were, however, susceptible to pharyngeal infection and subsequently became virus carriers. The proportion of animals becoming carriers appeared to vary with the degree of severity of the challenge.Vaccination before exposure to virus appeared to have little effect on the duration of the carrier state. No evidence was obtained of the spread of carrier virus to immune herds following the outbreak.Antibody titres during the outbreak were higher in the clinically infected animals than in the carrier animals and the uninfected animals. Evidence suggested that natural challenge boosted the titres of immune animals. After the outbreak, however, it was not possible to distinguish by their antibody titres between the carrier animal and the virus-negative animal.Antigenic studies on the strains of virus isolated are described.

The isolation and characterization of foot-and-mouth disease virus from clinically normal herds of cattle in Botswana

The results of a survey of the foot-and-mouth disease carrier state in three localities of an FMD enzootic area of Botswana are presented. The collection, storage and handling of the samples is mentioned and the isolation of virus on calf thyroid monolayer tissue cultures is described. Type SAT 3 virus was isolated from up to 20% of the animals sampled at periods between 7 and 12 months after natural infection. Sera were tested for all the animals from which virus was recovered and compared with similar numbers of sera from virus-negative animals. No correlation was found between the carrier state and serum antibody titres.

Antigenic studies are described which indicated not only an antigenic variation of some carrier viruses isolated from the outbreak strain but also antigenic differences between strains of carrier virus from different animals in the same herd. There was no evidence at the time of sampling of the persistence as carrier virus of the attenuated vaccine strains of FMDV used previously in the cattle sampled.

The results suggest that transference of carrier virus from animal to animal may occur in the absence of clinical infection.

The effects of trypanosomiasis on rural economy with special reference to the Sudan, Bechuanaland and West Africa

Trypanosomiasis, both of humans and of livestock, is one of the most important factors restricting economic development in Africa today. The present paper outlines how this disease is limiting agricultural, veterinary and forestry development in the Sudan, Bechuanaland and West Africa.The present tsetse-fly distribution is reviewed. Glossina palpalis and G. morsitans occur in the south Sudan and G. morsitans in the Ngamiland district of Bechuanaland; G. morsitans, G. palpalis and G. tachinoides are the most important species in West Africa.These tsetse flies have altered the cattle distribution in all three regions and, in addition to causing widespread disease, have created local overstocking problems in the tsetse-free grazing areas, and have enforced nomadism on breeding herds and economic loss in slaughter cattle along the trade cattle routes in West Africa.Human trypanosomiasis is not now such an urgent problem and public health measures have led to its control in all three areas.Increased agricultural development, which can be a successful and economic method of reclaiming land from tsetse flies, must be intensified in all three areas.Forest conservation policy comes into conflict with tsetse control measures only in West Africa.Detailed tsetse-fly surveys and research, on which future plans can be firmly based, are now urgently required.

Blood Pressure in Bushmen of the Kalahari Desert

The blood pressure was studied in 42 males and 36 females in 2 groups of nomadic Bushmen, living near Ghanzi in the Kalahari Desert, as well as in a third group of 21 Bushmen prisoners and farm laborers from the same region. The pressures were also "corrected" for arm girth.

The average systolic pressures were 108.4 mm. Hg (S.D. 11.4) for men and 112.8 mm. Hg (S.D. 14.6) for women. The average diastolic pressures were 66.2 mm. Hg (S.D. 6.9) and 69.6 mm. Hg (S.D. 8.0) for men and women, respectively. These pressures with stated exception, are considered to be lower than for most populations.

In the women, the systolic and diastolic pressures were higher than those in the men.

The blood pressure showed no tendency to rise with age, an observation in contrast to that found in most other populations. It was suggested that an increase of the blood pressure with age may be an indication of the existence of essential hypertension within that population.

The blood pressures of Bushmen prisoners and farm laborers were higher than those in nomadic Bushmen.

Further investigation is needed of the genetic and environmental factors affecting the blood pressure in the nomadic Bushmen.

Responses of Bushmen and Europeans on exposure to winter night temperatures in the Kalahari

Eight Bushmen and five Europeans were exposed during winter nights in the Kalahari desert to temperatures ranging from about 27°C to 2°C. Oxygen consumption and skin and rectal temperatures were measured over the period of 1frac12–2 hours of exposure. Comparison of increased metabolic rate with decreasing air temperatures measured in this study is made with similar data on young Norwegians. Bushmen and Europeans respond in a similar manner metabolically to the degree of cold stress experienced. Skin temperatures of the former tend to be lower and metabolism greater than in Europeans. The lower metabolic rate of Europeans is concluded to be due to the greater insulation afforded by their considerably larger subcutaneous fat deposits. These findings on the cold response of Bushmen contrast with those on Australian aborigines in comparable environmental conditions.

Submitted on January 4, 1960