Continuing presence of rinderpest virus as a threat in East Africa, 1983-1985

The re-emergence of rinderpest virus in East Africa in 1979 caused widespread outbreaks of disease and subclinical infection throughout the region until mid-1983. Subsequent massive emergency vaccination campaigns have been successful in eliminating clinical rinderpest from Tanzania and preventing its spread southwards. Unfortunately the virus is still endemic in north-eastern Uganda and has recently caused epidemic outbreaks with high mortality in cattle in that country. In Kenya, buffaloes (Syncerus caffer) in and around the Masai Mara game reserve have developed antibodies to rinderpest virus as recently as late 1984. Although there have been no outbreaks of clinical disease in Tanzania or Kenya from April 1983 to the end of 1985 this serological evidence plus the increasing incidence of clinical outbreaks in Uganda indicate that rinderpest virus still threatens East Africa. The substantial aid which has been provided to the region for rinderpest control must be maintained.     

A recent outbreak of rinderpest in East Africa

Rinderpest was brought under control in Kenya in 1976 but in April 1986 an outbreak of the disease occurred in cattle in Western Kenya, five kilometres from the Kenya-Uganda border. This was the first confirmed field outbreak of the disease in Kenya after a lull of over 10 years. Clinical disease was confined to unvaccinated zebu calves aged six to eight months from which rinderpest virus was isolated. High titres of antibodies to rinderpest virus were demonstrated in sera collected from sheep and goats that were grazing together with the affected cattle herds; there was, however, no evidence of clinical disease in these small ruminants and wildlife species in the affected area. The disease outbreak was rapidly stamped out by quarantine and vaccination.     

Re-infection of wildlife populations with rinderpest virus on the periphery of the Somali ecosystem in East Africa

We report surveillance for rinderpest virus in wildlife populations in three major ecosystems of East Africa: Great Rift Valley, Somali and Tsavo from 1994 to 2003. Three hundred and eighty wild animals were sampled for detection of rinderpest virus, antigen or genome and 1133 sampled for antibody in sera from Kenya, Uganda, Ethiopia and Tanzania from 20 species. This was done modifying for wildlife the internationally recommended standards for rinderpest investigation and diagnosis in livestock. The animals were selected according to susceptibility and preference given to gregarious species, and populations were selected according to abundance, availability and association with livestock. Rinderpest virus, antigen and/or genome were detected in Kenya; within Tsavo, Nairobi and Meru National Parks. Serological results from 864 animals (of which 65% were buffalo) from the region were selected as unequivocal; showing the temporal and spatial aspects of past epidemics. Recent infection has been only in or peripheral to the Somali ecosystem (in Kenya). Our evidence supports the hypothesis that wildlife is not important in the long-term maintenance of rinderpest and that wildlife are infected sporadically most likely from a cattle source, although this needs to be proven in the Somali ecosystem. Wildlife will continue to be a key to monitoring the remaining virus circulation in Africa.     

Rinderpest seroprevalence in wildlife in Kenya and Tanzania, 1982-1993

Eight hundred and thirty five serum samples collected from eight wild artiodactyl species in Kenya and Tanzania between 1982 and 1993 were tested for virus-neutralising (VN) antibodies to rinderpest (RP) virus. Antibodies were found in 116 of 344 buffaloes (Syncerus caffer) but not in the other species including 349 wildebeest (Connochaetes taurinus). Most of the antibody positive buffaloes were from the Maasai Mara-Serengeti ecosystem (MM-SE) and would have had opportunity for exposure to the virus during the epidemic of rinderpest in buffalo confirmed there in 1982. Buffalo born after 1985 did not have antibody indicating that virus stopped circulating in this population at or around that time. This second demonstration that RP virus disappears from the MM-SE is further evidence that these species are not permanent reservoirs of this virus. Re-infection of wildlife is transient and they remain valuable sentinels for infection in nearby domestic livestock.     

Rinderpest Vaccination and the Incidence and Development of Trypanosomosis in Cattle

An investigation was made into whether recent vaccination of cattle with tissue culture rinderpest virus would cause immunosuppression and lead to more frequent or more severe infection with trypanosomes in animals grazing in tsetse-infested areas. Herds of cattle on Galana Ranch in Kenya were divided, with approximately half of each herd being vaccinated with tissue culture rinderpest virus strain Kabete O, while the rest remained unvaccinated. The herds were then exposed to the risk of natural infection with trypanosomes on the ranch. Three experiments were performed during different seasons. Infections with Trypanosoma congolense and Trypanosoma vivax were frequently detected but there was no evidence that vaccinated animals were more likely to acquire trypanosome infections or to show a more severe disease than unvaccinated cattle. It is concluded that tissue culture rinderpest vaccine does not cause immunosuppression and can safely be used in cattle likely to be exposed to tsetse flies and trypanosomosis.     

Disease properties, geography, and mitigation strategies in a simulation spread of rinderpest across the United States

ABSTRACT: For the past decade, the Food and Agriculture Organization of the United Nations has been working toward eradicating rinderpest through vaccination and intense surveillance by 2012. Because of the potential severity of a rinderpest epidemic, it is prudent to prepare for an unexpected outbreak in animal populations. There is no immunity to the disease among the livestock or wildlife in the United States (US). If rinderpest were to emerge in the US, the loss in livestock could be devastating. We predict the potential spread of rinderpest using a two-stage model for the spread of a multi-host infectious disease among agricultural animals in the US. The model incorporates large-scale interactions among US counties and the small-scale dynamics of disease spread within a county. The model epidemic was seeded in 16 locations and there was a strong dependence of the overall epidemic size on the starting location. The epidemics were classified according to overall size into small epidemics of 100 to 300 animals (failed epidemics), epidemics infecting 3 000 to 30 000 animals (medium epidemics), and the large epidemics infecting around one million beef cattle. The size of the rinderpest epidemics were directly related to the origin of the disease and whether or not the disease moved into certain key counties in high-livestock-density areas of the US. The epidemic size also depended upon response time and effectiveness of movement controls.     

The production of peste des petits ruminants hyperimmune sera in rabbits and their application in virus diagnosis

Hyperimmune sera were produced by serial inoculation of rabbits with Vero cell-adapted, sucrose gradient-purified Nigerian peste des petits ruminants virus (PPRV) isolate. Two antisera produced, neutralized the homologous PPRV but not the heterologous rinderpest Kabette "O" virus. The antisera gave strong precipitin lines with purified PPRV antigens and were used to detect PPRV and rinderpest virus antigens from ante-mortem secretions and post-mortem tissue homogenates from PPR and rinderpest virus infected goats and cattle by the agar gel precipitation tests (AGPT). The hyperimmune sera gave good titration curves with both purified Nigerian goat and the United Arab Emirate wildlife PPRV isolates in the indirect enzyme linked immunosorbent assay (ELISA). Results of indirect ELISA showed that although there were some cross reactions with the rinderpest, canine-distemper and measles viruses, at 1:100 dilution, the antisera would give a positive signal with only the homologous PPR virus.     

Evidence of identification of peste des petits ruminants from goats in Egypt

Peste des petits ruminants virus was isolated from young goats in an outbreak of the disease for the first time in Egypt. Affected goats showed symptoms simulating rinderpest, disease in cattle. The mortality rate was about 30%, and morbidity reached 90%. History, clinical symptoms, postmortem lesions, and diagnosis were discussed.     

Outbreaks of rinderpest in wild and domestic animals in Nigeria

Rinderpest, although eradicated from Nigeria in 1974 after the JP15 campaign, was reintroduced into Sokoto state in 1980 and again into Borno state in 1983. The latter outbreak spread rapidly throughout Nigeria and severely reduced the cattle population. An estimated one million cattle were lost. An outbreak occurred at the Maiduguri zoo, in Borno state, in January 1983 and killed 15 elands and six sitatungas. In March 1983, rinderpest appeared in Yankari game reserve in adjoining Bauchi state and caused mortality in several species of wildlife. A total of 207 buffalo, 20 warthog, eight waterbuck and two bushbuck carcases were recovered. Rinderpest did not occur in wildlife in Nigeria after it was eradicated from cattle. In the Nigerian situation, the rinderpest appears to have been transmitted from cattle to wildlife. Vaccination of zoo animals and valuable animals in game reserves, preferably with a killed vaccine, and ring vaccination of livestock around game reserves can help to protect wildlife from rinderpest.     

Diagnosis of Rinderpest in Tanzania by a Rapid Chromatographic Strip-test

A simple chromatographic strip-test based on Clearview technology, is under development as a pen-side test for the detection of rinderpest antigen in eye swabs taken from cattle in the field. An outbreak of rinderpest occurred in the northern zone of Tanzania from late February to June 1997. The affected cattle exhibited very mild clinical signs, which made clinical diagnosis difficult. One hundred and seven eye swabs were collected from cattle suspected of infection with rinderpest. These were tested in the field using a prototype of the pen-side test and 13 (12.15%) of the samples were found to be positive for the presence of rinderpest antigen. These were confirmed by ICE. The positive cases were predominantly found in the Ngorongoro district. This demonstrates the usefulness of such a simple, rapid pen-side diagnostic assay, particularly when clinically `mild' strains of rinderpest are present.     

Observations on the pathogenicity for sheep and goats and the transmissibility of the strain of virus isolated during the rinderpest outbreak in Sri Lanka in 1987

The pathogenicity for sheep and goats of the virus strain that caused acute rinderpest in cattle and domestic buffalo in Sri Lanka after an interval of over 40 years has been examined. The results show that it can cause overt clinical disease in goats, but only mild or unapparent infection in sheep. The disease was transmitted from infected sheep to in-contact susceptible sheep and calves.     

Border disease in sheep caused by transmission of virus from cattle persistently infected with bovine virus diarrhoea virus.

Two outbreaks of border disease occurred on farms with sheep flocks and breeding cattle. The infection of the pregnant sheep was probably caused by transmission of virus from calves persistently infected with non-cytopathic bovine virus diarrhoea virus (BVDV) which were kept in close confinement with the ewes during mid-pregnancy. Border disease was also induced experimentally in eight lambs by exposing their dams at 38 to 78 days of gestation to a heifer persistently infected with BVDV. Both the natural and the experimental infections were characterised by typical signs such as 'hairy-shaker' lambs and high lamb mortality. The diagnosis was confirmed by virus isolations from live-born lambs, seroconversion and pathology. The study supports the assertion that cattle persistently infected with BVDV and in close contact with pregnant sheep, are an important source of strains of virus capable of causing border disease.     

Contacts between domestic livestock and wildlife at the Kruger National Park Interface of the Republic of South Africa

One of the most important transboundary animal diseases (TADs) in the southern African region is foot-and-mouth disease (FMD). In this region, a pathway for spread of FMD virus is contacts between cattle and certain species of wildlife. The objective of this study was to evaluate contacts between cattle and wildlife in the Kruger National Park (KNP) and the adjacent Limpopo province for the time periods October 2006 to March 2007 and April to September 2007. In this study, 87 livestock owners and 57 KNP field rangers were interviewed. Fifteen (17%) livestock owners reported contacts between wildlife and cattle. More livestock owners reported observing contacts between cattle and all wildlife species during October-March than April-September (p = 0.012). However, no difference was found between these periods for contacts between cattle and individual wildlife species. A total of 18 (32%) field rangers reported contacts between cattle and wildlife. The most common species-specific contacts were between cattle and buffalo (63/year), cattle and impala (17/year) and cattle and lion (10/year). There were no significant differences in rangers reporting observed contacts between cattle and wildlife during October-March versus April-September or between rangers reporting observed contacts outside versus within the KNP. Overall, there was no evidence of higher contact rates between cattle and wildlife in the study area during October-March compared to April-September. Contact data collected in this study can be used to better understand the transmission of FMD virus in this region.     

A reassessment of the dual vaccine against rinderpest and contagious bovine pleuropneumonia

In the light of the recent outbreaks of rinderpest in Africa a further assessment of the efficacy of the simultaneous inoculation of rinderpest virus vaccine and contagious bovine pleuropneumonia vaccine was undertaken. Groups of cattle were inoculated with a dual preparation of rinderpest vaccine virus and Mycoplasma mycoides subspecies mycoides or M mycoides alone. These groups were then challenged with M mycoides, first unsuccessfully by an in-contact challenge method and then by subcutaneous challenge. All animals were examined clinically after challenge for evidence of contagious bovine pleuropneumonia and serologically for rinderpest virus and M mycoides mycoides antibodies. There was no evidence that the serological response to the dual vaccine was in any way less than that to either agent given alone and no clinical disease was detected in these animals after in-contact challenge. However, after subcutaneous challenge, the dual vaccinated groups reacted similarly to an unvaccinated control group and unlike the group vaccinated only with M mycoides. This would indicate that the rinderpest virus component of the dual vaccine interfered with the ability of the M mycoides component to induce a fully effective immune response. In the pan African rinderpest campaign the use of the dual vaccine in areas where contagious bovine pleuropneumonia occurs should be carefully considered; in areas where the disease does not occur it is contraindicated.     

Rinderpest Antibody Detected in Sheep and Goats Before an Outbreak of Rinderpest Reported in Cattle in Northern Tanzania

In January 1997, serum samples from 1346 adult sheep and goats were tested by a competitive ELISA to determine the prevalence of rinderpest in the northern zone of Tanzania. Seroconversion rates of 20%, 13%, 9%, 7% and 3% in sheep and goats were recorded in Ngorongoro, Monduli, Hai, Arumeru and Simanjiro districts, respectively. The low profile and insidious nature of the rinderpest virus involved caused very mild disease in cattle in some of these area. The mild signs associated with this outbreak of rinderpest resulted in difficulty in its diagnosis. In these circumstances, the presence of rinderpest antibody in sheep and goats served as a valuable and effective indicator of the rinderpest outbreak in cattle.     

Echinococcosis in Kenya: transmission characteristics, incidence and control measures

Kenya has the highest reported incidence of human hydatid disease in the world. Up to about 30% of cattle, 15% of goats and 13% of sheep harbour the infection. The causative agent of the disease in Kenya is Echinococcus granulosus and a complex strain picture of this parasite has been postulated to occur. The domestic dog is the main definitive host of E. granulosus in Kenya but infection in wild carnivores has also been reported. Hydatid cysts have also been found in wild herbivores. Although the domestic cycle has been shown to be the most important mode of transmission of the disease, a sylvatic cycle is also known to exist. The etiology of hydatid disease, the strain differentiation of E. granulosus found in Kenya, and the role that wildlife plays in the transmission cycle is reviewed. The current trends in the incidence of hydatid disease in man and livestock, and the efforts being made to control the disease are also discussed.     

The detection of antibody against peste des petits ruminants virus in Sheep,Goats, Cattle and Buffaloes

Monoclonal antibody-based competitive ELISA (C-ELISA) has been used for the specific measurement of antibodies to peste des petits ruminants (PPR) viruses in sheep, goats, cattle and Buffalo. Serum samples from sheep (n = 232), goats (n = 428), cattle (n = 43), buffalo (n = 89) were tested. The animals had not been vaccinated against rinderpest or PPR. Findings suggested that the sero-positive cases were significantly higher in sheep (51.29%) than in goats (39.02%) (P = 0.002). The overall sero-prevalence of PPRV in small ruminants was 43.33%. The PPR antibodies seroprevalence was 67.42% in buffalo and 41.86% in cattle which was significantly higher in buffalo (P = 0.005). The overall sero-prevalence of PPRV in large ruminants was 59.09%. Cattle and buffalo sera showed a high prevalence of antibody against PPR virus which may explain the difficulty experienced in achieving high post-vaccination immunity levels against rinderpest. Because antibodies against PPR virus are both cross-neutralizing and cross-protective against rinderpest virus, further vaccination in the presence of antibodies against PPR virus may be a waste of national resources. It was also suggested that antibodies to PPR virus could prevent an immune response to the rinderpest vaccine. This paper presents serological evidence for the transmission of PPR virus from sheep and goats to cattle and buffalo and highlights the need to include PPR serology in the sero-monitoring programme to give a better indication of national herd immunity of sheep and goats against PPR.     

Improved isolation of rinderpest virus in transformed bovine T lymphoblast cell lines.

Bovine T lymphoblast cell lines transformed by the protozoan Theileria parva were compared with bovine kidney (BK) and Vero cells for their ability to isolate various strains of rinderpest virus from tissues and infected secretions. All of the strains of rinderpest virus that were tested, including attenuated cell-culture, caprinised and lapinised vaccines, and both mild and virulent pathogenic strains, readily induced syncytial cytopathic effect (cpe) in T lymphoblasts. The cpe could often be detected within one day of inoculation of lymphoblasts, whereas it took three to 14 days to appear in Vero and BK cells. Using lymphoblasts it was possible to reisolate rinderpest virus from nine of 42 swabs collected from three cattle experimentally infected with an isolate from a recent outbreak of mild disease whereas the same swabs yielded only one reisolate on BK cells. It was also possible using the lymphoblasts to detect infectious virus in the ocular, nasal and oral secretions of goats and rabbits infected with caprinised and lapinised virus, respectively. Peste des petits ruminants virus appeared to grow as rapidly as rinderpest virus in the lymphoblasts whereas canine distemper virus readily induced cpe on first passage but less readily on subsequent passage. Measles virus induced relatively little cpe when inoculated into lymphoblasts and did not appear to passage in these cells. The lymphoblasts are easy to maintain in culture and since they rapidly recovered 11 isolates from 37 diagnostic samples could prove useful in laboratories carrying out rinderpest diagnosis.     

Epidemiological investigations of the 2001 foot-and-mouth disease outbreak in Argentina

A total of 2126 herds, an attack rate of 0.82 per cent, were affected during an epidemic of foot-and-mouth disease in Argentina in 2001. The spatial and temporal distribution of the epidemic was investigated using nearest-neighbour and spatial scan tests and by estimating the frequency distributions of the times to intervention, and distances and times between outbreaks. The outbreaks were clustered and associated significantly (P<0.01) with herd density; 94 per cent were located in the Pampeana region, where the cattle population is concentrated, which had an attack rate of 1.4 per cent. The clustering results suggested that the virus had spread locally between outbreaks. Most of the outbreaks were separated by one day and the maximum distance between outbreaks was almost 2000 km, indicating that the infection spread rapidly over large distances. The index outbreak was detected more than 15 days after the primary outbreak, and restrictions on the movement of cattle were probably not enforced until about one month after infection occurred. As in other major epidemics, the period between the first outbreaks and the effective application of control strategies was probably crucial in determining the progress of the epidemic.