New insights into the role of ticks in African swine fever epidemiology

African swine fever (ASF), one of the most important diseases of swine, is present in many African countries, as well as in eastern Europe, Russia and Sardinia. It is caused by a complex virus, ASF virus (ASFV), for which neither vaccine nor treatment is available. ASFV affects swine of all breeds and ages, and also replicates in soft ticks of the genus Ornithodoros, facilitating ASFV persistence and reocurrence of disease. Depending on the involvement of these ticks, and the presence or not of sylvatic asymptomatic animals, several epidemiological cycles have been identified. The disease persists in East and southern African countries in a sylvatic cycle between O. porcinus (of the O. moubata species complex) and common warthogs. In some countries a domestic pig-tick cycle exists, whereas in other regions, notably West Africa, the role of soft ticks has not been demonstrated, and ASFV is transmitted between domestic pigs in the absence of tick vectors. Even in several East and Central African countries which have the sylvatic or domestic cycle, the majority of outbreaks are not associated with ticks or wild suids. In Europe, O. erraticus was detected and identified as a crucial vector for ASF maintenance in outdoor pig production on the Iberian Peninsula. However, in most parts of Europe, there is a lack of information about the distribution and role of Ornithodoros ticks in ASF persistence, particularly in eastern regions. This article reviews ASF epidemiology and its main characteristics, with a special focus on the distribution and role of soft ticks in ASF persistence in different settings. Information abouttick detection, control measures and future directions for research is also included.

Review of the sylvatic cycle of African swine fever in sub-Saharan Africa and the Indian ocean

African swine fever (ASF) is a major limiting factor for pig production in most of the countries in Sub-Saharan Africa and the Indian Ocean. In the absence of vaccine, a good understanding of the ecology and epidemiology of the disease is fundamental to implement effective control measures. In selected countries of Southern and East Africa, the association between Ornithodoros moubata ticks and warthogs has been described in detail in the literature. However, for many other countries in the region, information related to the sylvatic cycle is lacking or incomplete. In West African countries, for instance, the role of wild pigs in the epidemiology of ASF has never been demonstrated and the existence and potential impact of a sylvatic cycle involving an association between soft ticks and warthogs is questionable. In other countries, other wild pig species such as the bushpigs (Potamochoerus spp.) can also be asymptomatically infected by the virus but their role in the epidemiology of the disease is unclear and might differ according to geographic regions. In addition, the methods and techniques required to study the role of wild hosts in ASF virus (ASFV) epidemiology and ecology are very specific and differ from the more traditional methods to study domestic pigs or other tick species. The aim of this review is (i) to provide a descriptive list of the methodologies implemented to study the role of wild hosts in African swine fever, (ii) to compile the available knowledge about the sylvatic cycle of ASFV in different regions of Sub-Saharan Africa and the Indian Ocean in addition to the one that has been described for East and Southern Africa, and (iii) to discuss current methodologies and available knowledge in order to identify new orientations for further field and experimental surveys.

Review of African swine fever: transmission, spread and control

African swine fever is one of the most important and serious diseases of domestic pigs. Its highly contagious nature and ability to spread over long distances make it one of the most feared diseases, since its devastating effects on pig production have been experienced not only in most of sub-Saharan Africa but also in western Europe, the Caribbean, Brazil and, most recently, the Caucasus. Unlike most diseases of livestock, there is no vaccine, and therefore prevention relies entirely upon preventing contact between the virus and the susceptible host. In order to do so it is necessary to understand the way in which the virus is transmitted and spreads. By implementing strict biosecurity measures that place barriers between the source of virus and the pigs it is possible to prevent infection. However, this has implications for free-ranging pig husbandry systems that are widespread in developing countries. Attempts to produce a vaccine are ongoing and new technology offers some hope for the future, but this will not remove the necessity for implementing adequate biosecurity on pig farms.

African swine fever in Mozambique: review, risk factors and considerations for control

African swine fever (ASF) is the most important disease that constrains pig production in Mozambique. Until 1994 it was apparently restricted to the central and northern provinces, but since 1994 outbreaks have been experienced throughout the country. ASF causes severe economic losses both in the small commercial sector and among the large numbers of small-scale producers in the family sector in rural and peri-urban areas. The history of ASF in Mozambique since its first confirmation in 1960 is briefly reviewed, recent outbreaks are reported, and the available information on the virus genotypes that have been responsible for some of the outbreaks is presented. Epidemiological factors that contribute to ASF outbreaks and strategies for limiting the negative effects of the disease in the different pig farming sectors in Mozambique, including raising farmer and community awareness, are discussed.

An investigation into natural resistance to African swine fever in domestic pigs from an endemic area in southern Africa

A population of domestic pigs in northern Mozambique with increased resistance to the pathogenic effects of African swine fever (ASF) virus was identified by the high prevalence of circulating antibodies to ASF virus. An attempt was made to establish whether the resistance in this population was heritable. Some of these pigs were acquired and transported to a quarantine facility and allowed to breed naturally. Offspring of the resistant pigs were transferred to a high security facility where they were challenged with two ASF viruses, one of which was isolated from one of the Mozambican pigs and the other a genetically closely-related virus from Madagascar. All but one of the 105 offspring challenged developed acute ASF and died. It therefore appears that the resistance demonstrated by these pigs is not inherited by their offspring, or could not be expressed under the conditions of the experiment. The question remains therefore as to the mechanism whereby pigs in the population from which the experimental pigs were derived co-existed with virulent ASF viruses.

International trade in livestock and livestock products: the need for a commodity-based approach

International animal health standards designed to facilitate safe trade in livestock and livestock products are set by the Office International des Epizooties (OIE) under the Sanitary and Phytosanitary Agreement of the World Trade Organization (WTO) and documented in the OIE's Terrestrial Animal Health Code. A core principle of the Code is the need for countries to eradicate important transboundary animal diseases (TADs) to reduce the risk of exporting disease to trading partners. International food safety standards are set by the Codex Alimentarius Commission, administered jointly by the World Health Organization and the Food and Agriculture Organization of the United Nations. The goal of global eradication of most TADs is unachievable for the foreseeable future, other than in the case of rinderpest, and this prevents many countries, especially developing nations, from engaging in international trade under WTO rules. This paper proposes an alternative, commodity-based approach to the formulation of international animal health and food safety standards, based on the fact that different commodities pose very different risks when it comes to the spread of human and animal pathogens. Therefore, the risk mitigation strategies required are equally commodity-dependent. The authors conclude that more focused commodity standards would improve access to international markets for all countries, especially those in the developing world. For this objective to be realised, credible and independent certification is required.

Multifactorial mortality in bongos and other wild ungulates in the north of the Congo Republic

Wildlife mortality involving bongos, Tragelaphus eurycerus, and other ungulates was investigated in the north of the Congo Republic in 1997. Four bongos, one forest buffalo, Syncerus caffer nanus, and one domestic sheep were examined and sampled. Although an outbreak of rinderpest had been suspected, it was found that the animals, which had been weakened by an Elaeophora sagitta infection and possibly also by adverse climatic conditions, had been exsanguinated and driven to exhaustion by an unusual plague of Stomoxys omega.

[The 1996 epizootic of African swine fever in the Ivory Coast]

African swine fever was reported for the first time in the Côte d'Ivoire on 16 April 1996, in Abidjan. The epizootic resulted in the death of 135,000 pigs, equivalent to 29% of the pig population, of which 80% came from the commercial sector. By November, the outbreaks had stabilised and were then eliminated. All epidemiological evidence showed that the active form of disease ceased in September 1996. A variety of factors were responsible for limiting and then halting progression of the disease from the end of August 1996, including a new strategy which gave priority to local information, better control of the situation, depopulation of the infected area in Abidjan, the epidemiological containment of most cases within the villages, and also the assistance and direct involvement of the Food and Agriculture Organization (FAO) of the United Nations. The contribution of the FAO was decisive. It provided a diagnosis of the situation, recommended emergency measures, developed a control strategy, ensured the implementation of the control programme, set up a diagnostic laboratory unit and provided training for staff, slaughtered and destroyed any remaining pigs, set up and implemented a local information programme, developed and implemented a scheme for sentinel animals and for epidemiological surveillance, and designed, performed and analysed an epidemiological survey. From the commencement of the epizootic, two major shortcomings became apparent: inadequate dissemination of information, and a shortage of technical resources allocated for the control of African swine fever. These two shortcomings were compounded by other technical and socio-economic constraints.

Vermeersiekte caused by Geigeria burkei Harv. subsp. burkei var. hirtella merxm. in the northern province of South Africa

The 1st field outbreak of vermeersiekte induced by Geigeria burkei Harv. subsp. burkei var. hirtella Merxm, is reported. It is also the first recorded outbreak of this disease in the arid sweet bushveld of the Northern Province of South Africa. The toxicosis was experimentally reproduced in a sheep following daily intraruminal administration of 2.5-5.0 g/kg dried, milled plant material for 18 consecutive days. Neither the sheep in the field outbreak nor the ewe in the experiment exhibited any signs of regurgitation of rumen contents (vermeersiekte). All developed only the stiff or paretic/paralytic forms of the disease. Serum activities of CK and GGT were slightly raised in clinically affected sheep (n = 11) during the field outbreak, and serum activities of AST, GLDH, GGT, LDH and CK increased in the ewe dosed with the plant material. Analysis of dried, milled Geigeria plant material confirms that this species is moderately nutritious.

Disease and mortality in captive wild dogs (Lycaon pictus)

A retrospective survey on the causes of disease and death in captive wild dogs (Lycaon pictus) (n = 87) presented for examination and investigation from 1983 to 1995, revealed that 50 were less than a week old, 13 were between a week and 1 year of age, 7 were less than 5 years old, and 6 were older than 5 years. The age of 11 adult dogs could not be determined. The cause of death could not be determined in the majority of neonates but 37 probably died of exposure and 13 of septicaemia and pulmonary lesions. Various causes of trauma, including aggression and siblicide, were diagnosed in 13 wild dogs. Lesions of the lungs, kidneys, heart, pancreas, uterus, intestines and skin were diagnosed respectively in 4, 6, 3, 3, 5, 5 and 2 of the cases. An aberrant behavioural pattern was diagnosed in a hand-reared wild dog.

Tuberculosis in buffaloes (Syncerus caffer) in the Kruger National Park: spread of the disease to other species

Tuberculosis, caused by Mycobacterium bovis, was recently diagnosed in a cheetah (Acinonyx jubatus), two lions (Panthera leo) and a chacma baboon (Papio ursinus) from the Kruger National Park (KNP). It is assumed that they contracted the disease directly or indirectly from tuberculous buffaloes in the park. Tuberculous granulomatous lesions in the lungs were extensive and constituted the predominant changes in all three animal species. These pulmonary lesions included tuberculous bronchiolitis and cavitation which would facilitate dissemination of M. bovis into the environment. Spread of the disease to free-ranging species (in which it has not previously been reported) that may act as maintenance hosts of the infection, is a matter of serious concern.

Swayback in a blesbok (Damaliscus dorcas phillipsi) and a black wildebeest (Connochaetes gnou)

Ataxia associated with myelopathy and low liver copper concentrations is described in a blesbok (Damaliscus dorcas phillipsi) and black wildebeest (Connochaetes gnou) from the Karoo Nature Reserve, Graaff-Reinet. This syndrome, which occurs in neonatal and delayed forms, has been described in sheep, goats, pigs and domesticated red deer, but reports in other ungulates, including antelope, are very rare and generally unconfirmed by histopathological examination. The 2 animals examined exhibited a typical pattern of Wallerian degeneration in selected tracts of the spinal cord. Many blesbok in the reserve are markedly pale in colour. Fading of the hair is also associated with copper deficiency in ungulates. High lamb mortality occurs as a result of the ataxia and threatens the survival of the blesbok herd in the reserve. Confirmation of low liver copper concentrations in affected animals offers direction towards the solution of the problem.

Mortality in chickens associated with blister beetle consumption

Mortality in young chickens was associated with blister beetle consumption. Two species of these insects, Cyaneolytta sp. and Cylindrothorax sp., were found in the chickens' crops, and erosive lesions in the gastrointestinal tract were compatible with blister beetle poisoning (cantharidiasis).

Selenium toxicosis with focal symmetrical poliomyelomalacia in postweaning pigs in South Africa

An outbreak of paralysis in finisher pigs in South Africa after ingestion of feed containing 54,581 mg/kg of selenium is described. The main and entirely consistent lesion was bilaterally symmetrical focal poliomalacia of the ventral horns of the spinal cord, which was most severe and consistent in the lumbar intumescence. Acute and subacute lesions were characterized by malacia with large numbers of gitter cells. The main features of chronic lesions were loss of neurons and gliosis. Focal degeneration and necrosis of the myocardium and skeletal muscles were also consistent, but there were fewer specific changes. Endothelial swelling, mild fibrinoid degeneration and perivascular leukocytic infiltration were present in the acute stage. Dermatitis, coronitis and hoof sloughing, usually present in more chronic cases of intoxication, were not a feature of the present outbreak, although alopecia and crusting were evident on the backs of a few pigs several weeks after the episode of intoxication. Serum-and tissue-selenium levels were elevated in the early stages after intoxication. Serum levels were nearly normal in chronic cases two months after the episode, while liver and kidney levels were still higher than normal. Higher levels were found in liver, kidney and serum than in muscle, with the highest levels in the kidney. Less than 20% of affected pigs recovered sufficiently to be marketed.

A chronic cardiomyopathy in feedlot cattle attributed to toxic levels of salinomycin in the feed

The clinical signs and pathology in an outbreak of toxicity in feedlot cattle attributed to the ingestion of toxic levels of the ionophore antibiotic salinomycin over an extended period of 11 weeks are described. Thirty-nine out of 380 cattle developed signs consistent with cardiac failure and 8 of these died. Clinical signs included dyspnoea, tachypnoea, tachycardia and exercise intolerance. Two cattle were necropsied and in one there were macroscopic lesions suggestive of congestive heart failure, namely pulmonary oedema, hydrothorax and hepatomegaly. Histopathology revealed a chronic cardiomyopathy characterised principally by extensive myocardial fibre atrophy with multifocal hypertrophy and interstitial and replacement fibrosis. Hepatic and pulmonary lesions were consistent with those of congestive cardiac failure. The myocardial lesions in this outbreak were similar to those encountered in cases of a chronic toxicity associated with the ingestion of litter derived from poultry rations containing ionophores (ionophore-associated poultry litter toxicity). Hence, the clinical and pathological findings in this outbreak indicate that in cattle, the prolonged ingestion of ionophores over several weeks may result in the development of chronic myocardial lesions comparable to those of IAPLT but significantly different from those encountered in the more traditional acute outbreaks of ionophore toxicity as described in the literature.

A review of mycotic nasal granuloma in cattle, with a report on three cases

Three cases of nasal mycotic granuloma containing fungal cells and hyphae in cattle are described. In 2 animals a mucopurulent or purulent nasal discharge was seen clinically, and epistaxis in the third. Histologically, ulceration of the nasal mucosa and a severe granulomatous inflammation of the nasal submucosa with eosinophils as the predominant cell type were evident in the cattle. Non-pigmented fungal cells identified as chlamydospores and short septate hyphae were demonstrated in giant cells and extracellularly within the granulomatous reactions. In one case, the fungal elements were frequently surrounded by homogeneous eosinophilic (Splendore-Hoeppli) material. Dematiaceous fungi, Bipolaris sp. and Drechslera sp., were isolated from 2 cases. Mycology was not performed on the third animal.

Evidence for cryptosporidial infection as a cause of prolapse of the phallus and cloaca in ostrich chicks (Struthio camelus)

Cloacas of male ostrich chicks that had suffered prolapse of the phallus and cloaca were compared with cloacas of normal ostrich chicks of both sexes from the same area. Heavy infection of the cloacal and bursal tissue with Cryptosporidium sp. was present in all the cases of prolapse, while no cryptosporidia were observed in the normal chicks. Histopathological lesions as described in cryptosporidial infection in other species were present in the infected cloacas. These included loss of the microvillous border and epithelial hyperplasia and degeneration, which was indicated ultrastructurally by vacuolation of the apical cytoplasm, swelling of organelles, and nuclear changes. It is suggested that these lesions, in combination with the anatomy of the male ostrich cloaca, may be responsible for prolapse of the phallus and cloaca.

Pulmonary and hepatic lesions associated with suspected ganskweek (Lasiospermum bipinnatum) poisoning in cattle

A field outbreak of poisoning of cattle by ganskweek (Lasiospermum bipinnatum [Thunb.] Druce) in the Molteno district is described. In addition to the typical histopathological lesion of zonal hepatic necrosis and haemorrhage, pulmonary lesions of interstitial pneumonia, emphysema and bronchial epithelial changes similar to those described in experimental ganskweek poisoning in sheep are reported.

Congenital cardiac defects in two closely related Jersey calves

This paper describes similar congenital cardiac anomalies in 2 half sibling Jersey calves. Both calves had ventricular septal defects with dextraposition of the aorta and hypertrophy of the right ventricle, consistent with Eisenmenger's complex. One of the calves also had patent foramen ovale. The 2 calves had been sired by the same bull, and collateral relationships existed between the sire and the 2 dams.

Prolapse of the phallus and cloaca in the ostrich (Struthio camelus)

The incidence of cloacal prolapse in ostrich chicks hatched and raised on the Oudtshoorn Experimental Farm during the 1992-1993 breeding season was investigated. The condition which occurred primarily in male chicks, affected 14.65% of the total number of chicks hatched. The mortality rate amongst chicks with cloacal prolapse was very high. Although the pathogenesis and aetiology of the condition is unknown, a species of Cryptosporidium was present in large numbers in affected cloacas. Treatment with systemic antibiotics was found to be effective in some cases.

Thymic necrosis in slaughtered Nile crocodiles

Foci of necrosis with formation of heterophilic granulomas in the medullary region of the thymus were found in apparently normal slaughtered crocodiles from 4 South African crocodile farms. The comparative pathology of these lesions is discussed. From these preliminary results it may be assumed that thymic necrosis occurs commonly in intensively reared slaughter crocodiles. The cause of this condition, however, remains obscure.

Pox virus infection in captive juvenile caimans (Caiman crocodilus fuscus) in South Africa

Light grey macules developed on the skin and in the mouths of juvenile caimans, (Caiman crocodilus fuscus) (n = 8), kept in the quarantine section of the reptile park at the National Zoological Gardens, Pretoria, Republic of South Africa. The gross, histopathological and ultrastructural features of the lesions were commensurate with pox virus infection. This outbreak closely resembled the disease described elsewhere in 3 juvenile captive caimans.