Age determination and age structure of a striped fieldmouse,Rhabdomys pumilio,population from the Cape Flats

The validity of predicting the age of Rhabdomys pumilio by age-related changes in tooth appearance, dimensions and position, in body mass and head-body length is tested against 47 known-age mice. Body mass can be used to determine the age of individuals of less than 7 weeks old (≤ 26 g). Thereafter, the only reliable technique of age determination Involves a visual evaluation of the degree of molar tooth wear. Five wear classes are described and used to assess the age of 780 R. pumilio collected during a five-year period. The annual cycles of population age structure and size were dependent on seasonal recruitment and were Influenced by the duration of the peak breeding period. The growth rate, especially of females, is reduced in winter, and maturity appears to be delayed until spring, when breeding commences.     

Amblyomma tick feeding in relation to host health

Tropical Animal Health and Production - The tickAmblyomma variegatum has been shown by field and controlled laboratory experiments to have a direct causal relationship with severe clinical...     

Food preferences of the vlei rat (Otomys Irroratus) and the four-striped mouse (Rhabdomys pumilio)

The food preferences of O. irroratus and R. pumilio have been examined in laboratory tests. O. irroratus prefers green vegetation including herbs, shrubs and grasses whereas R. pumilio prefers fruits and seeds. Both species eat insects in the laboratory, but they are more important in the natural diet of R. pumilio than O. irroratus. O. irroratus readily eats grasses which are not consumed by R. pumilio. Partial dietary overlap occurs in the laboratory which suggests that some degree of competition for fruits and seeds will occur at certain seasons in natural populations.     

The epizootiology and control of heartwater and other tick-borne diseases of cattle in South Africa

The history of the main bovine tick-borne diseases occurring in South Africa and the role Onderstepoort played in their identification and control is briefly reviewed. The present attitudes regarding the control of tick-borne diseases, taking into account their complexity, is discussed. Gaps in our knowledge regarding heartwater epizootiology and possible future studies are defined.     

A survey of Karoo tick paralysis in South Africa

Recent research interest in Karoo tick paralysis and its vector. Ixodes rubicundus, prompted this survey to determine the economic implications of this disease. The survey indicated relatively high losses caused by the condition, identified the stock involved and provided data on the incidence of paralysis and on the control methods employed. Recommendations are made to institute chemical control earlier in the season to attempt better containment of the problem.     

Relative resistance of six cattle breeds to the tick Boophilus decoloratus in South Africa

Adult females of the tick Boophilus decoloratus were removed from 6 breeds of cattle on 2 farms in the Northern Transvaal. Highest numbers of female ticks were collected from Simmentaler, followed by Santa Gertrudis, Bonsmara, Afrikaner, Brahman and Nguni. Resistance levels of each breed to B. decoloratus was positively correlated with the amount of Bos indicus genes in the breed, with the exception of Nguni, which is a sanga type but not pure B. indicus.     

The ecology of the African vectors of heartwater, with particular reference to Amblyomma hebraeum and Amblyomma variegatum

The hosts, sites of attachment, life cycle, habitat requirements and seasonal abundance of Amblyomma astrion, Amblyomma cohaerens, Amblyomma gemma, Amblyomma hebraeum, Amblyomma lepidum, Amblyomma marmoreum, Amblyomma pomposum, Amblyomma sparsum, Amblyomma tholloni and Amblyomma variegatum, the 10 potential vectors of heartwater in Africa, are listed. Factors influencing the distribution and abundance of the ticks as well as interactions with other species and the role of predators and pathogens are discussed.     

The infection ofGlossina morsitans weid byTrypanosoma brucei in relation to the parasitaemia in the mouse host

Summary G. morsitans were fed upon white mice infected withT. brucei TREU667, within 24 hours of emergence from the puparium. Infection rates in the flies averaged 5.8 per cent mature infections with a maximum of 15.4 per cent in one experiment. Irradiation of mice with 400r X-rays 24 hours before infection was found to slightly enhance the infection rate in flies. Flies are more readily infected when the blood-meal contains 50–20,000 trypanosomes per mm³ and 10–20,000 short stumpy forms per mm³. With the strain ofT. brucei used, suitable conditions in the mouse occur subsequent to 12 days after infection.

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Sumario MoscasG. morsitans fueron alimentadas sobre ratones blancos infectados conT. brucei TREU 667, dentro de las 24 horas de su emergencia del puparium. Las tasas de infección en las moscas promediaron 5.8 por ciento de infecciones maduras con un maximo de 15.4 por ciento en un experimento. La irradiación de ratones con 400r de rayos X por 24 horas antes de la infección acrecentó ligeramente la tasa de infección en las moscas. Las moscas son mas facilmente infectables cuando la sangre de los ratones contiene de 50–20,000 tripanosomas por mm³ y 10–20,000 formas cortas de mu?ón por mm³. Con la cepa deT. brucei usada, las condiciones adecuadas en el ratón occurren subsecuente a los 12 dias despues de la infección.

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Résumé DesG. morsitans écloses depuis moins de 24 heures ont été nourries sur souris blanche infectée avecTrypanosoma brucei. Les taux d'infection chez les mouches ont atteint une moyenne de 5,8 p. 100 de formes infectantes avec un maximum de 15,4 p. 100 dans une expérience. L'irradiation des souris aux rayons X à la dose de 400 r, 24 heures avant l'infection, a augmenté légèrement le taux d'infection chez les mouches. Les mouches sont plus aisément infectées quand le repas de sang contient de 50 à 20,000 trypanosomes par mm³ et 10 à 20,000 formes courtes et trapues par mm³. Avec la souche deT. brucei utilisée, ces taux d'infection favorables apparaissent chez la souris 12 jours après l'infection.

     

The dispersion of the Karoo paralysis tick, Ixodes rubicundus, within a naturally infested population of sheep in South Africa

The ratio of variance to mean (s2/means) of numbers of Ixodes rubicundus (males and females) per sheep was used as a measure of the dispersion pattern of this tick within a naturally infested population of sheep. Sheep were divided into two groups, one with previous contact with I. rubicundus and the other with no previous contact. Samples of 10 sheep from each group were searched for ticks on a weekly basis for 19 weeks during the winter of 1986. In each group, both male and female ticks had an s2/means ratio greater than 1 for the majority of observation periods indicating an aggregated dispersion pattern. The degree of aggregation was greater with increasing density of the ticks. The implications of these results are discussed both in relation to sampling procedures and potential control strategies.     

Striped mice, Rhabdomys pumilio, and other murid rodents as hosts for immature ixodid ticks as in the Eastern Cape Province

Striped mice, Rhabdomys pumilio, were trapped over a period of 17 months in the Thomas Baines Nature Reserve, and placed in cages, over water, until all the ticks they harboured had detached. The mice were then returned to the reserve. Four ixodid tick species were recovered from the mice of which the larvae and nymphs of Rhipicephalus follis and Rhipicephalus simus were the most numerous. Most larvae of R. follis detached from mice trapped from March to July, and most nymphs in March and from June to September. Most larvae of R. simus detached from mice trapped from December to March, and most nymphs from January to March and during May and June. Seven ixodid tick species were collected from striped mice, house rats, Rattus rattus, vlei rats, Otomys spp. and Praomys sp. captured in the vicinity of human dwellings or animal holding facilities in the Grahamstown district. The striped mice captured in the Thomas Baines Reserve harboured considerably larger numbers of ticks than any of the rodent species in the more urbanized localities.     

The control of heartwater in west Africa—Present and future

Tropical Animal Health and Production - Heartwater (HW) is the name given to the acute, febrile disease of ruminants caused by infection with the obligate intra-cellular rickettsiaCowdria...     

Some observations on the sero-prevalence of heartwater and tick infestation in Zambian goats

A survey was carried out to define the distribution of heartwater in goats that originated from six districts in communal grazing semi-arid areas of Zambia. A total of 181 samples (40.1%) out of 451 serum samples from adult goats were positive for Ehrlichia ruminantium antibodies after screening using indirect MAP-1B antigen ELISA technique with statistically significant differences (P < 0.01) between the six districts. Out of 1 036 adult goats examined for tick infestation, 105 were infested by ticks, with Amblyomma species being the most dominant tick encountered. Amblyomma variegatum, which is the vector for heartwater transmission in Zambia constituted 42.4% of the tick species, identified. The overall tick infestation rate was 10% while the tick:goat ratio was 2.1:1. Amblyomma variegatum appears to be widespread throughout the study area, as are antibodies to E. ruminantium.     

The carrier status of sheep, cattle and African buffalo recovered from heartwater

Sheep, cattle and the African buffalo (Syncerus caffer) were shown to remain carriers of heart-water (caused by Cowdria ruminantium) for long periods after recovery; 223, 246 and 161 days, respectively. Transmission was achieved using adults of the southern African bont tick (Amblyomma hebraeum) that had fed as nymphs on recovered animals. Our findings differ from those of other workers who attempted transmission using nymphs that had fed as larvae on recovered animals or with blood from recovered animals.     

The colonization and life-cycles of Musca lusoria, Musca xanthomelas and Musca nevilli, vectors of Parafilaria bovicola in South Africa

Thriving, permanent colonies of Musca xanthomelas and later of Musca nevilli were successfully established. However, because of the low reproduction potential of Musca lusoria a small colony only was kept for a limited period until life-cycle studies were completed. Larvae were reared on fresh dung from cattle fed lucerne, while in general adults were fed 0.3% citrated ox-blood, whole milk powder, sugar crystals, fresh dung and water. M. nevilli could be colonized only when ox-liver was substituted for ox-blood. A comparison of the life-cycles of M. lusoria and M. xanthomelas under laboratory conditions at a constant temperature of approximately 27 degrees C, 60% R.H. and 24 h illumination revealed major differences between these 2 vector species. M. lusoria deposits single larvae at intervals of approximately 2 days and a female can produce up to 27 in her life-time. An M. xanthomelas female can lay up to 4 batches of eggs, with as many as 33 eggs per batch, at intervals of approximately 5 days. A single female can produce a maximum of 94 eggs. M. lusoria, however, showed survival advantages over M. xanthomelas in that its larvae reached the pupal stage at least a day sooner and its adults survived more than twice as long. The life-cycles of M. xanthomelas and M. nevilli were similar in the laboratory, except for adult dietary requirements. The mean number of mature oocytes in the ovaries of M. nevilli, however, was only 15.7 compared with 26.1 in M. xanthomelas.     

A survey of cattle tick control practices in the eastern Cape Province of South Africa.

Current cattle tick control practices and producer attitudes towards tick control in the eastern Cape Province of South Africa are discussed. These were ascertained from answers to a questionnaire survey to which 31.2% of farmers responded. In general, producers favoured intensive tick control. Beef and dairy farmers had a definite preference for synthetic pyrethroid acaricides, the majority followed a 25 times p.a. treatment frequency and most changed acaricides because of price. Beef producers favoured pour-on application of acaricides while the majority of dairy producers utilized plunge dipping. Producers who used hand spray techniques experienced the highest percentage of confirmed acaricide resistance. A costs of R11.27 for acaricide treatment per bovine per annum was calculated from data gained in this survey. A cost index of 2,496 was calculated by relating acaricide cost to the prevailing price of beef in the region. Only a small number of producers used heartwater, babesiosis and anaplasmosis vaccines. Relative tick borne disease mortality ratios indicated higher heartwater mortalities at high acaricide treatment frequencies. These results are discussed in relation to the tick control regimes practised.     

Waterfowl abundance and diversity in relation to season,wetland characteristics and land-use in semi-arid South Africa

We studied waterfowl abundance and diversity in relation to season (wet vs dry), wetland characteristics (vegetation and morphometrics) and land-use in a semi-arid agricultural region of South Africa to determine how waterfowl respond to various wetland characteristics, particularly those of permanent agricultural ponds.Wetlands were visited during the wet (n = 215) and dry (n = 178) seasons of 1997 and species' abundances, and wetland and upland characteristics were recorded. Canonical correspondence analyses and multiple regressions determined which wetland and upland characteristics were most strongly associated with waterfowl density and species richness for both the wet and dry season. Overall, diving ducks were not abundant in the wet season, and were rare to absent in the dry season. Divers only responded positively to the characteristics of natural wetlands, including greater surface area, percent coverage of emergent vegetation, and high (ungrazed) shoreline vegetation. Of six species of dabbling ducks present during the wet season, occurrence of three co-varied with wetland and upland characteristics associated with agriculture, namely permanent water, and agricultural grains in the dry season. Being largely grazers, geese responded positively to the higher proportions of bare shoreline, characteristically surrounding agricultural ponds. Because only a few species associated with artificial waterbodies, natural wetlands should be conserved to protect waterfowl diversity in semi-arid South Africa.     

Distribution, habitats and role as intermediate host of the freshwater snail, Bulinus forskalii, in South Africa

This paper focuses on the geographical distribution and habitats of Bulinus forskalii, the snail intermediate host of the conical fluke of equids, Gastrodiscus aegyptiacus as reflected by the 1209 samples in the database of the National Freshwater Snail Collection of South Africa. The 362 different loci on record represent an extensive distribution in KwaZulu-Natal Province, the Limpopo Province, the coastal areas of the Eastern Cape Province and the south-eastern part of the North West Province. Although it was recorded from all types of water-body represented in the database, the highest percentages of samples were recovered from dams (30.4%) and brooks (28.2%). The majority of samples came from perennial habitats (59.1%), 60.7% from habitats with standing water, 54.0% from habitats with clear water and 71.8% from habitats of which the water was described as fresh. The majority of samples (39.5%) were collected in habitats of which the substratum was recorded as muddy. The highest percentage of samples, by far (81.5%), was collected in habitats that fell within the mean yearly temperature interval ranging from 15-20 degrees C. An integrated decision tree constructed from the data in the database indicated that temperature and type of water-body played a decisive role in determining the presence of B. forskalii in a given area. The results of experimental exposure to miracidia of a local strain of both Schistosoma haematobium and Schistosoma mattheei in the laboratory indicated that a local strain of B. forskalii was incompatible with both these strains of parasite. Research to clarify the role of B. forskalii in the transmission of both Calicophoron microbothrium and G. aegyptiacus in South Africa, is recommended.     

The immunization of calves against heartwater: subsequent immunity both in the absence and presence of natural tick challenge

Cattle, vaccinated as calves with Cowdria ruminantium-infected tick stabilate, were challenged 6, 12 and 24 months later. In the absence of tick challenge, vaccination of calves induced a partial immunity against subsequent challenge at 12 and 24 months. In animals exposed to ticks, the resistance was no better than that of control, unvaccinated cattle. When they were challenged at 6 months of age there was no difference between vaccinated and unvaccinated calves, either in the absence or presence of tick challenge, and all the animals manifested a high degree of natural resistance. This study therefore suggests that the value of vaccinating Afrikander-cross calves in heartwater endemic areas should be further investigated. The indirect fluorescent antibody (IFA) test proved to be a valuable means of monitoring the serological response of vaccinated animals and detecting the sero-conversion of animals exposed to tick infection. On one hand, there was good correlation between the febrile reaction and the results of the IFA test on the sera of vaccinated and control cattle challenged with the heartwater agent, in that all sero-positive animals were resistant to challenge. On the other hand, though, a considerable percentage of the animals that were serologically negative were also resistant to challenge.     

Updated distribution and host records for the argasid tick Ornithodoros (Pavlovskyella) zumpti: A potential vector of African swine fever virus in South Africa

African swine fever virus (ASFV) causes a lethal and contagious disease of domestic pigs. In South Africa, the virus historically circulated in warthogs and ornithodorid ticks that were only found in warthog burrows in the north of the country. Regulations implemented in 1935 to prevent transfer of infected animals or products to the south initially proved effective but from 2016 there have been outbreaks of disease in the south that cannot be traced to transfer of infection from the north. From 1963 there were widespread translocations of warthogs to the south, initially from a source considered to be free of ornithodorid ticks. We undertook to determine whether sylvatic circulation of ASFV occurs in the south, including identification of potential new vectors, through testing extralimital warthogs for antibody and ticks for virus. Results of testing warthogs for antibody and other species of ticks for virus will be presented separately. Here we report finding Ornithodoros (Pavlovskyella) zumpti ticks in warthog burrows for the first time. This occurred in the Eastern Cape Province (ECP) in 2019. Since African swine fever was recognised in the ECP for the first time in 2020 and outbreaks of the disease in domestic pigs continue to occur there, priority should be given to determining the distribution range and vector potential of O. (P.) zumpti for ASFV.