The evaluation of five serological assays in determining seroconversion to peste des petits ruminants virus in typical and atypical hosts

Peste des petits ruminants (PPR) is an infectious viral disease, primarily of small ruminants such as sheep and goats, but is also known to infect a wide range of wild and domestic Artiodactyls including African buffalo, gazelle, saiga and camels. The livestock-wildlife interface, where free-ranging animals can interact with captive flocks, is the subject of scrutiny as its role in the maintenance and spread of PPR virus (PPRV) is poorly understood. As seroconversion to PPRV indicates previous infection and/or vaccination, the availability of validated serological tools for use in both typical (sheep and goat) and atypical species is essential to support future disease surveillance and control strategies. The virus neutralisation test (VNT) and enzyme-linked immunosorbent assay (ELISA) have been validated using sera from typical host species. Still, the performance of these assays in detecting antibodies from atypical species remains unclear. We examined a large panel of sera (n = 793) from a range of species from multiple countries (sourced 2015-2022) using three tests: VNT, ID VET N-ELISA and AU-PANVAC H-ELISA. A sub-panel (n = 30) was also distributed to two laboratories and tested using the luciferase immunoprecipitation system (LIPS) and a pseudotyped virus neutralisation assay (PVNA). We demonstrate a 75.0-88.0% agreement of positive results for detecting PPRV antibodies in sera from typical species between the VNT and commercial ELISAs, however this decreased to 44.4-62.3% in sera from atypical species, with an inter-species variation. The LIPS and PVNA strongly correlate with the VNT and ELISAs for typical species but vary when testing sera from atypical species.

A study on transmission of Peste des petits ruminants virus between dromedary camels and small ruminants

INTRODUCTION

In recent years Peste des petits ruminants (PPR) disease caused several epidemics in a wide range of susceptible hosts. The ability of the peste des petits ruminants virus (PPRV) to cross the species barrier necessitates further research, particularly on disease circulation and cross-species transmission between typical and atypical hosts to guide and facilitate the eradication program anticipated by the Food and Agriculture Organization (FAO) and the World Organization for Animal Health (OIE) in 2030. The aim of this study is to explore the role of dromedary camels as transmitters for PPR.

METHODOLOGY

Four experiments were carried out on clinically healthy seronegative camels, sheep and goats. In experiment I, the animals were inoculated with a PPR- positive suspension of camel pneumonic lung homogenate. In the other three experiments either sheep and goats were inoculated and after three days were housed with camels or vice versa.

RESULTS

Marked clinical signs suggestive of PPR were seen in sheep and goats while camels showed mild infection. Severe clinical signs of PPR were seen in sheep and goats when kept with inoculated camels. Postmortem examination revealed PPR lesions in all inoculated animals including camels.

CONCLUSIONS

This study showed that dromedary camels infected with PPRV can transmit the disease to sheep and goats, even when they developed mild clinical signs.

Assessment of the control measures of category A diseases of the Animal Health Law: Infection with rinderpest virus (Rinderpest)

EFSA received a mandate from the European Commission to assess the effectiveness of control measures against diseases included in the Category A list according to Regulation (EU) 2016/429 on transmissible animal diseases ('Animal Health Law'). This opinion belongs to a series of opinions where these control measures are assessed, with this opinion covering the assessment of control measures for rinderpest (RP), the only animal disease to have been globally eradicated. In this opinion, the AHAW Panel reviewed the effectiveness of: (i) clinical and laboratory sampling procedures, (ii) monitoring period and (iii) the minimum radius of the protection and surveillance zone, and the minimum length of time the measures should be applied in these zones. The general methodology used for this series of opinions has been published elsewhere. The transmission kernels used for the assessment of the minimum radius of the protection and surveillance zones are shown. Several scenarios for which control measures had to be assessed were agreed prior to the assessment. Considering that RP has been eradicated globally, a re-emergence that is not stopped in its early phases could have a devastating impact on animal health and the economy. The panel concludes that no suitable strategies are available to entirely mitigate the risk associated with granting derogations from killing of animals in an affected establishment or for animal movements. Therefore, the panel recommends to not grant any derogations. The monitoring period of 21 days was assessed as effective, except for the hypothetical first re-emergence of RP, when lack of awareness and diagnostic capability may extend the time to detection. It was concluded that the protection and the surveillance zones would contain 90% and > 99%, respectively, of the infections from an affected establishment. Enlarging the protection zone to 4 km would contain the disease spread with 95% probability.

Identification of Differential Responses of Goat PBMCs to PPRV Virulence Using a Multi-Omics Approach

Peste des petits ruminants (PPR) is an acute transboundary infectious viral disease of small ruminants, mainly sheep and goats. Host susceptibility varies considerably depending on the PPR virus (PPRV) strain, the host species and breed. The effect of strains with different levels of virulence on the modulation of the immune system has not been thoroughly compared in an experimental setting so far. In this study, we used a multi-omics approach to investigate the host cellular factors involved in different infection phenotypes. Peripheral blood mononuclear cells (PBMCs) from Saanen goats were activated with a T-cell mitogen and infected with PPRV strains of different virulence: Morocco 2008 (high virulence), Ivory Coast 1989 (low virulence) and Nigeria 75/1 (live attenuated vaccine strain). Our results showed that the highly virulent strain replicated better than the other two in PBMCs and rapidly induced cell death and a stronger inhibition of lymphocyte proliferation. However, all the strains affected lymphocyte proliferation and induced upregulation of key antiviral genes and proteins, meaning a classical antiviral response is orchestrated regardless of the virulence of the PPRV strain. On the other hand, the highly virulent strain induced stronger inflammatory responses and activated more genes related to lymphocyte migration and recruitment, and inflammatory processes. Both transcriptomic and proteomic approaches were successful in detecting viral and antiviral effectors under all conditions. The present work identified key immunological factors related to PPRV virulence in vitro.

Wide circulation of peste des petits ruminants virus in sheep and goats across Nigeria

Peste des petits ruminants (PPR) is a highly contagious viral disease that mainly affects goats and sheep in Asia, Africa and the Middle East, and threatens Europe [R.E.1]. The disease is endemic on the African continent, particularly in West Africa, and is a major factor driving food insecurity in low-income populations. The aim of this research study was to carry out surveillance, genetic characterisation and isolation of recently circulating PPR viruses (PPRV) in sheep and goats from the six agro-ecological zones of Nigeria. A total of 268 post-mortem tissue samples of lung and mesenteric ganglia were collected from clinically suspected sheep and goats in 18 different states, of which five never previously sampled. The presence of PPRV was confirmed using a reverse-transcription coupled with a polymerase chain reaction (RT-PCR) assay. A total of 72 samples, 17 sheep (6%) and 55 goats (21%), were found to be PPR positive. Positive samples were distributed in almost all states, except Kano, where PPR was detected in previous studies. The PPRV-positive samples were further confirmed by sequencing or virus isolation in areas where the infection had never previously been detected. These results confirm the active circulation of PPRV across all six agro-ecological zones of Nigeria, and consequently, the need for introducing strict measures for the control and prevention of the disease in the country.

Assessment of the control measures of the category A diseases of Animal Health Law: peste des petits ruminants

EFSA received a mandate from the European Commission to assess the effectiveness of some of the control measures against diseases included in the Category A list according to Regulation (EU) 2016/429 on transmissible animal diseases ('Animal Health Law'). This opinion belongs to a series of opinions where these control measures will be assessed, with this opinion covering the assessment of control measures for peste des petits ruminants (PPR). In this opinion, EFSA and the AHAW Panel of experts review the effectiveness of: (i) clinical and laboratory sampling procedures, (ii) monitoring period and (iii) the minimum radii of the protection and surveillance zones, and the minimum length of time the measures should be applied in these zones. The general methodology used for this series of opinions has been published elsewhere; nonetheless, the transmission kernels used for the assessment of the minimum radii of the protection and surveillance zones are shown. Several scenarios for which these control measures had to be assessed were designed and agreed prior to the start of the assessment. The monitoring period of 21 days was assessed as effective, except for the first affected establishments detected, where 33 days is recommended. It was concluded that beyond the protection (3 km) and the surveillance zones (10 km) only 9.6% (95% CI: 3.1-25.8%) and 2.3% (95% CI: 1-5.5%) of the infections from an affected establishment may occur, respectively. This may be considered sufficient to contain the disease spread (95% probability of containing transmission corresponds to 5.3 km). Recommendations provided for each of the scenarios assessed aim to support the European Commission in the drafting of further pieces of legislation, as well as for plausible ad-hoc requests in relation to PPR.

Molecular epidemiology of peste des petits ruminants virus in Nigeria: An update

Peste des petits ruminants (PPR) is a highly contagious viral disease that mainly affects goats and sheep in Asia, Africa and the Middle East. The PPR virus (PPRV) can be classified into four genetically distinct lineages (I, II, III and IV). All have been historically present in Africa, except the Asian lineage IV that has been spreading across the globe and across Africa in recent decades. Previous studies have identified the presence of lineage IV in Nigeria since 2010. In the present study, samples were taken from 429 small ruminants with PPR symptoms across Nigeria in 2017–2020 to provide an update on the distribution and genetic diversity of PPRV in the country. Sequences from a portion of the PPRV nucleoprotein (N) gene were obtained from 91 samples, 90 belonging to lineage IV and one to lineage II. Phylogenetic analysis identified at least four lineage IV sub‐clusters in Nigeria, grouping samples across multiple regions. Our results suggest extensive endemic circulation of a wide range of PPRV strains across Nigeria and across borders with neighbouring countries, underlining the difficulty involved in controlling the disease in the region.

Peste des Petits Ruminants at the Wildlife-Livestock Interface in the Northern Albertine Rift and Nile Basin, East Africa

In the recent past, peste des petits ruminants (PPR) emerged in East Africa causing outbreaks in small livestock across different countries, with evidences of spillover to wildlife. In order to understand better PPR at the wildlife-livestock interface, we investigated patterns of peste des petits ruminants virus (PPRV) exposure, disease outbreaks, and viral sequences in the northern Albertine Rift. PPRV antibodies indicated a widespread exposure in apparently healthy wildlife from South Sudan (2013) and Uganda (2015, 2017). African buffaloes and Uganda kobs <1-year-old from Queen Elizabeth National Park (2015) had antibodies against PPRV N-antigen and local serosurvey captured a subsequent spread of PPRV in livestock. Outbreaks with PPR-like syndrome in sheep and goats were recorded around the Greater Virunga Landscape in Kasese (2016), Kisoro and Kabale (2017) from western Uganda, and in North Kivu (2017) from eastern Democratic Republic of the Congo (DRC). This landscape would not be considered typical for PPR persistence as it is a mixed forest-savannah ecosystem with mostly sedentary livestock. PPRV sequences from DRC (2017) were identical to strains from Burundi (2018) and confirmed a transboundary spread of PPRV. Our results indicate an epidemiological linkage between epizootic cycles in livestock and exposure in wildlife, denoting the importance of PPR surveillance on wild artiodactyls for both conservation and eradication programs.

Peste des petits ruminants infection in domestic ruminants in Sudan

The existence of peste des petits ruminants (PPR) in domestic ruminants and camels in Sudan during 2008-2012 was investigated. Lung tissues and serum samples were randomly collected from sheep, goats, cattle, and camels at different areas of Sudan. A total of 12,384 serum samples were collected from clinically healthy 7413 sheep, 1988 camels, 1501 cattle, 1459 goats, and 23 gazelles at different areas in the Sudan. They were examined for PPR antibodies using competitive ELISA (cELISA). The overall detected seroprevalence of PPR in tested sera was 49.4%; seroprevalence values within species were 67.1, 48.2, 25.8, 2.1, and 21.7% in sheep, goat, cattle, camels, and gazelles, respectively. The highest seroprevalence (68.1%) was observed in sera collected from Darfur states, then the central states (54.3%). A total of 1276 lung tissue samples (623 sheep, 324 cattle, 220 camels, and 109 goats) were collected. The majority of lung samples were collected from clinically healthy animals that showed lesions on PM in slaughterhouses (95%) and during PPR outbreaks; samples were tested for PPR antigen using immunocapture ELISA (IcELISA). PPR antigen was detected in 233 out of the 1276 tested samples (18.3%). Positive results were observed in samples collected from clinically healthy and diseased animals. The observed prevalence values in each species were 33.6, 21.1, 15.4, and 12.3% in camel, goat, sheep, and cattle, respectively. PPR antigen was detected in samples from different areas; however, the highest prevalence (63.9%) was found in samples collected from the eastern states, then Khartoum state (28%). Trials for virus isolation were done in different cell cultures. Out of 30 IcELISA-positive samples inoculated in primary bovine and ovine kidney cells, Vero cells, the PPR virus was successfully isolated from 15 (eight sheep, five camels, and two goats) samples in the three cell culture types. Using RT-PCR, PPRV nucleic acid was detected in all 25 IcELISA-positive tested samples.

Peste des Petits Ruminants Virus

Peste des petits ruminants virus (PPRV) causes a severe contagious disease of sheep and goats and has spread extensively through the developing world. Because of its disproportionately large impact on the livelihoods of low-income livestock keepers, and the availability of effective vaccines and good diagnostics, the virus is being targeted for global control and eventual eradication. In this review we examine the origin of the virus and its current distribution, and the factors that have led international organizations to conclude that it is eradicable. We also review recent progress in the molecular and cellular biology of the virus and consider areas where further research is required to support the efforts being made by national, regional, and international bodies to tackle this growing threat.

Impact and Epidemiological Investigations into the Incursion and Spread of Peste des Petits Ruminants in the Comoros Archipelago: An Increased Threat to Surrounding Islands

Late October 2012, a great number of deaths of unknown origin occurred in goat herds in the suburbs of Ngazidja, located in the Comoros archipelago. Few weeks later, laboratory testing requested by the animal health authorities resulted in the identification of peste des petits ruminants (PPR) infection. Notably, the Index case could be attributed to a sick goat imported from Tanzania. Viral isolation was successful from the lungs leading to the whole N nucleoprotein gene sequencing. Phylogenetic analysis revealed that the strain belongs to the lineage III which includes strains of eastern African origin. In addition, to evaluate the impact of PPR on the Comorian indigenous domesticated ruminant population, a cross-sectional PPR serological survey was conducted between April and July 2013. A low overall PPRV antibody prevalence 2.24% (95% CI [1.38; 3.08]) was detected with a Grande Comore prevalence of 3.34% (IC = [2.09; 4.63]) with a limited spread of the disease mainly due to farm practices such as limited contacts between farm animals and rapid slaughtering of sick animals.

Emergence of Lineage IV Peste des Petits Ruminants Virus in Ethiopia: Complete Genome Sequence of an Ethiopian Isolate 2010

Isolates of peste des petits ruminants virus (PPRV) can be segregated genetically into four lineages. For decades, lineages I-III have been reported across Africa whilst lineage IV has predominantly circulated across Asia. However, the lineage distribution is currently changing in Africa. Importantly, full genome sequence data for African field isolates have been lacking. Here, we announce the first complete genome sequence of a field isolate of peste des petits ruminants virus (PPRV) from East Africa. This isolate was derived from the intestine of a goat suffering from severe clinical disease during the 2010 outbreak in Ethiopia. The full genome sequence of this isolate, PPRV Ethiopia/2010, clusters genetically with other lineage IV isolates of PPRV, sharing high levels of sequence identity across the genome. Further, we have carried out a phylogenetic analysis of all of the available African partial N gene and F gene PPRV sequences to investigate the epidemiology of PPRV with a focus on the emergence of different lineages of PPRV in Africa.

Asian lineage of peste des petits ruminants virus, Africa

Interest in peste des petits ruminants virus (PPRV) has been stimulated by recent changes in its host and geographic distribution. For this study, biological specimens were collected from camels, sheep, and goats clinically suspected of having PPRV infection in Sudan during 2000-2009 and from sheep soon after the first reported outbreaks in Morocco in 2008. Reverse transcription PCR analysis confirmed the wide distribution of PPRV throughout Sudan and spread of the virus in Morocco. Molecular typing of 32 samples positive for PPRV provided strong evidence of the introduction and broad spread of Asian lineage IV. This lineage was defined further by 2 subclusters; one consisted of camel and goat isolates and some of the sheep isolates, while the other contained only sheep isolates, a finding with suggests a genetic bias according to the host. This study provides evidence of the recent spread of PPRV lineage IV in Africa.

[Morbillivirus infections of ruminants: the nearly eradicated rinderpest and the "peste des petits ruminants", an expanding disease in the South and a threat for Europe]

Rinderpest (RP) and peste des petits ruminants (PPR) are contagious viral diseases of domestic and wild ruminants producing high mortality. They are caused by viruses belonging to the Morbillivirus genus, Paramyxoviridae family. Control tools (vaccines and specific diagnostic tests) exist for these two diseases. They have been successfully used during the global rinderpest eradication programme (GREP) and the disease is expected to be eradicated by 2010. In contrast, a similar programme does not exist for PPR, which is still spreading in Africa and Asia. The persistence of PPR in Turkey and its recent introduction in Morocco, make the disease a real threat for Europe. Improvement of control measures against PPR would benefit from the development of a marker vaccine and its companion serological test, thus allowing the differentiation between infected and vaccinated animals (DIVA vaccines and tests). The recent development of reverse genetics for morbilliviruses offers this new possibility.

Examples of probable host-pathogen co-adaptation/co-evolution in isolated farmed animal populations in the mountainous regions of North Vietnam

In Vietnam, for a number of specific geographical and historical reasons, the mountainous areas have preserved an exceptional diversity of wild and domestic animal species of high socioeconomic interest. This endemic genetic diversity fosters a rapid response to environmental change in mostly isolated local communities and, in particular, fosters the constant adaptation of ecosystems common to humans and farmed and wild animal populations and pathogens. During a 2-year study carried out in several mountainous regions of North Vietnam near the Chinese border, we surveyed 1697 breeders in 249 villages and gathered 5815 biological samples among the four main domesticated species of food animals: chickens, cattle, buffaloes, and goats. Serological analyses were carried out by ELISA on 726 sera in order to assess the prevalence of antibodies specific to two major diseases suspected to be present in the region: avian influenza (AI) and peste des petits ruminants (PPR). The results reported here reveal the presence of antibodies specific to AI, but not the H5N1 highly pathogenic strain, and the presence of antibodies specific to PPR, confirming that this disease, never previously described in Southeast Asia, is present in this region, with no mortality and little or no evidence of clinical cases. These are probably situations of co-evolutive epidemiological equilibrium between pathogen populations, which may have lost their virulence, and animal populations that have acquired genetic resistances over generations, either naturally or through genetic introgression from related wild species better adapted to such pathogens. These results suggest the need for more research, both short-term and, more globally, long-term.

Long-term storage at tropical temperature of dried-blood filter papers for detection and genotyping of RNA and DNA viruses by direct PCR

In tropical countries the diagnosis of viral infections of humans or animals is often hampered by the lack of suitable clinical material and the necessity to maintain a cold chain for sample preservation up to the laboratory. This study describes the use of filter papers for rapid sample collection, and the molecular detection and genotyping of viruses when stored over long periods at elevated temperatures. Infected blood was collected on filter papers, dried and stored at different temperatures (22, 32 and 37 degrees C) for various periods (up to 9 months). Two animal viruses, African swine fever, a large double-stranded DNA virus and Peste des Petits Ruminants, a negative single-stranded RNA virus, were used to validate the method. Filter papers with dried blood containing virus or control plasmid DNA were cut in small 5mm(2) pieces and added directly to the PCR tube for conventional PCR. Nucleic acid from both viruses could still be detected after 3 months at 32 degrees C. Moreover, the DNA virus could be detected at least 9 months after conservation at 37 degrees C. PCR products obtained from the filter papers were sequenced and phylogenetic analysis carried out. The results were consistent with published sequences, demonstrating that this method can be used for virus genotyping.

Mapping the Peste des Petits Ruminants virus nucleoprotein: identification of two domains involved in protein self-association

For Mononegavirales, the template for transcription and replication is not the naked RNA but the nucleoprotein (N) encapsidated genomic and anti-genomic RNA. Because of this central role in the replication of these viruses, N has been the subject of numerous structural and functional mapping studies. Here, we report on the cloning of the Peste des Petits Ruminants virus (PPRV) N gene into the baculovirus vector and the expression of the protein in insect cells. By electron microscopy observation, we have shown that this recombinant PPRV N forms nucleocapsid-like particles in insect cells in the absence of other PPRV proteins, as reported for other paramyxoviruses. As it is known that the formation of these particles is first linked to the self-assembly of N, we have made several deletions in the PPRV N gene and expressed these mutants in insect cells. Analysis of these proteins by immunoprecipitation and electron microscopy observation enabled us to map the N-N interaction domains into two regions of PPRV N: aa 1-120 and 146-241. The fragment aa 121-145, which is not conserved within the morbillivirus group, is also required for the formation/stability of the nucleocapsid helical structure.

The threat of peste des petits ruminants: progress in vaccine development for disease control

Peste des petits ruminants (PPR) is a highly contagious animal disease caused by a virus in the genus Morbillivirus, family Paramyxoviridae. This infection is responsible for high morbidity and mortality in sheep and goats and in some small wild ruminant species. The huge number of small ruminants, which are reared in the endemic areas makes PPR a serious disease threatening the livelihood of poor farmers. Taking advantage of the closely relationship between rinderpest and PPR viruses, the attenuated rinderpest vaccine was used in the control of PPR. It is now replaced by the homologous attenuated PPR vaccine. Unfortunately, animals that have received this vaccine cannot be distinguished serologically from infected animals. With the advent of DNA recombinant technology, efforts are being made to develop effective PPR marker vaccines to enable such differentiation and which would allow countries to implement both vaccination and disease surveillance programmes at the same time.

Mapping and structural analysis of B-cell epitopes on the morbillivirus nucleoprotein amino terminus

By analysing the antigenic structure of the morbillivirus nucleoprotein (N) using a competitive-binding assay of monoclonal antibodies (mAbs), six different antigenic sites were identified previously. By using Pepscan methodology complemented by analysis of truncated N proteins, a better characterization of five of these antigenic sites was provided: I, II, III, IV and VI. mAbs specific to Rinderpest virus, defining antigenic sites II, III and IV, and those common to four morbilliviruses, delineating sites I and VI, were analysed in the present study. It was found that all but one mapped to the same region, between aa 120 and 149 of N. However, the mAb 3-1 epitope was located in the carboxy-terminal region (aa 421-525). This result may indicate the high immunogenicity of the amino-terminal variable region, at least in the mouse. It was surprising that the epitope of mAb 33-4, antigenic site VI, which recognized all morbilliviruses so far tested, was located in one of the two non-conserved regions between morbillivirus N proteins. It is shown that the conserved amino acid motif (126)EAD(128)----(131)F-------(148)EN(149) is critical for epitope constitution and recognition.

Peste des Petits Ruminants (PPR) Outbreak in Tajikistan

The occurrence of outbreaks of peste des petits ruminants (PPR) in three districts of Tajikistan is described. The causal strain (PPR Tajikistan) was characterized and the sequence of its N gene was compared with that of 43 other strains isolated since 1968 in Africa, the Middle East and Asia. The study demonstrated (1) the value of the N gene as a target in comparing isolates obtained over an extended period of evolution, and (2) that clustering was related to the geographical origin of strains.

Early detection of viral excretion from experimentally infected goats with peste-des-petits ruminants virus

We observed 15 goats for 9 days after subcutaneous infection with 10(3) TCID(50) with isolates of peste-des-petits ruminants virus from Africa and India and five concurrent, uninfected control goats. Typical clinical signs of the infection were present in all 15 infected goats by day 8 and in most by day 6 and some signs were present by day 4. However, 6 out of 15 goats already have detectable virus shedding by day 3 and four more were shedding by day 4 and every goat had virus shedding for at least 1 day before the recognition of clinical signs. This experiment indicates that incubatory carriers therefore might play a role in the transmission of PPRV among small ruminants.

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.

Surveillance of wildlife as a tool for monitoring rinderpest and peste des petits ruminants in West Africa

The authors provide a report on the surveillance of rinderpest virus (RPV) and peste des petits ruminants virus (PPRV) in the wildlife population in Côte d'Ivoire. For this purpose, 266 animals from nine different species, selected according to susceptibility and abundance, were captured and sampled from Comoé, Marahoué and Lamto Parks. Two hundred and forty seven sera and 214 nasal swabs were collected and analysed by competitive enzyme-linked immunosorbent assay (cELISA) and reverse-transcriptase polymerase chain reaction (RT-PCR) techniques, respectively. Serological data demonstrated that RPV was not circulating within the national Parks and estimated the PPR seroprevalence to be less than 1%. The analysis of the nasal swabs revealed no cases of RPV infection, but PPRV infection was detected in four species, including buffalo. To minimise the cost of the study without affecting the sensitivity of the test, samples were pooled into different groups and submitted to RT-PCR using nucleoprotein gene specific primers. The RT-PCR used in this study, which was derived from the method developed by Couacy-Hymann et al. in 2002, was followed by a hybridisation step using internal specific probes to confirm the identity of the deoxyribonucleic acid product. When used in conjunction with a cELISA this method accurately demonstrated the absence of rinderpest viral persistence in Côte-d'Ivoire.

Evaluation of the virulence of some strains of peste-des-petits-ruminants virus (PPRV) in experimentally infected West African dwarf goats

Different isolates of peste-des-petits-ruminants virus (PPRV) from outbreaks in Africa and India were investigated for virulence in West African dwarf goats in the Ivory Coast. Six groups of five animals received a virulent suspension of various strains of virus at a concentration of 10(3) TCID(50)/mL and the goats were observed for 15 days after infection. The Côte-d'Ivoire 89 (CI89), Guinea Conakry and Bissau Guinea PPRV strains caused a peracute disease; the India-Calcutta strain caused acute disease; the Sudan-Sennar strain produced an acute to mild disease, while the Nigeria 75/1 wild-type strain caused a mild disease and the animals recovered. The viruses studied contained examples of PPRV from specific lineage groups based on their nucleoprotein PPRV gene. This experiment indicated that virulence characteristics might be a useful marker to help classify PPRV isolates.

Evaluation of novel diagnostic tools for peste des petits ruminants virus in naturally infected goat herds

A survey was carried out in two goat herds during a single peste des petits ruminant (PPR) outbreak. Clinical examination showed that animals belonging to the West African Dwarf species had severe symptoms while those belonging to the West African long-legged species had mild symptoms. To confirm and to monitor the disease in each species, the study required specific monoclonal antibody-based diagnostic tools. An association of shedding of PPR virus (PPRV) and acute or mild clinical signs of the disease could be demonstrated by the rinderpest virus (RPV)/PPRV immunocapture ELISA assay. Between 85 and 100% of nasal secretions obtained from clinically diseased goats during the PPR outbreak reacted positively. Parallel serological surveillance for specific measurement of PPR antibodies revealed that between 34.4 and 88.5% of animals with no detectable virus were, however, able to seroconvert and therefore seemed to demonstrate that PPR subclinical infections do occur. Antibodies were shown to impair the RP heterologous vaccination. This evaluation offers new prospects for diagnosis and management of PPRV infection as well as for RPV control.

Antibody seroprevalences against peste des petits ruminants (PPR) virus in camels, cattle, goats and sheep in Ethiopia

A questionnaire-survey data indicated that 26% of 276 farmers reported the presence of respiratory disease in their herds in 2001. The incidence was perceived as "high" in small ruminants and camels, but as "low" in cattle. Simultaneously, 2815 serum samples from camels (n=628), cattle (n=910), goats (n=442) and sheep (n=835) were tested. The peste des petits ruminants (PPR) antibody seroprevalence was 3% in camels, 9% in cattle, 9% in goats and 13% in sheep. The highest locality-specific seroprevalences were: camels 10%, cattle 16%, goats 22% and sheep 23%. The animals had not been vaccinated against rinderpest or PPR. Antibody seroprevalences detected in camels, cattle, goats and sheep confirmed natural transmission of PPR virus under field conditions.

Monoclonal antibody-based competitive ELISA for simultaneous detection of rinderpest virus and peste des petits ruminants virus antibodies

An experimental competitive enzyme-linked immunosorbent assay (morbillivirus cELISA) using a recombinant N antigen (rRPV N) expressed in a baculovirus and a ruminant morbillivirus (RPV and PPRV)-specific monoclonal antibody (P-13A9) was developed for simultaneous detection of rinderpest virus (RPV) and peste des petits ruminants virus (PPRV) antibodies and its diagnostic performance was evaluated. A set of known reference antisera against RPV and PPRV belonging to different lineages, experimental sera from cattle vaccinated for a RPV of Asian lineage, and field sera from cattle and sheep/goat populations known to be positive (West Africa) and negative (Korea) for RPV and PPRV were used for the evaluation. Morbillivirus cELISA results on the panel of experimental RPV and PPRV antisera showed high correlation (r=0.97) between the whole virus and the rRPV N antigens, suggesting that the rRPV N contains a ruminant morbillivirus-specific antigenic determinant recognized by the P-13A9 and it may be suitable as an ELISA antigen in place of the whole virus. Morbillivirus cELISA detected anti-RPV and anti-PPRV antibodies in all reference RPV and PPRV antisera containing VN titers >/=1:8, suggesting that the assay can simultaneously detect antibodies against RPV and PPRV. Anti-RPV antibody was detected by morbillivirus cELISA in vaccinated cattle as early as the VNT and continued to be detectable by both the cELISA and the VNT until termination of the study. When applied to field samples from Africa, morbillivirus cELISA showed good agreement with a RP cELISA kit (kappa value of 0.86) in bovine sera and with a peste des petits ruminant cELISA kit (kappa value of 0.81) in caprine/ovine sera. Usefulness of morbillivirus cELISA using the rRPV N protein was discussed.

Development of a dual recombinant vaccine to protect small ruminants against peste-des-petits-ruminants virus and capripoxvirus infections

A recombinant capripoxvirus vaccine containing a cDNA of the peste-des-petits-ruminants virus (PPRV) fusion protein gene was constructed. A quick and efficient method was used to select a highly purified recombinant virus clone. A trial showed that a dose of this recombinant as low as 0.1 PFU protected goats against challenge with a virulent PPRV strain.

Goat immune response to capripox vaccine expressing the hemagglutinin protein of peste des petits ruminants

Sheep-pox and capripox are contagious diseases of domestic small ruminants for which the causal agent is a poxvirus classified into the Capripoxvirus genus. Viruses of this group have a host range specific to sheep, goats, cattle, and possibly buffalo. Thus, they are clearly indicated as vectors for the development of recombinant vaccines for peste des petits ruminants (PPR). Here we report the immune response of goats inoculated with a recombinant capripox-PPR hemagglutinin.

Rapid and sensitive detection of peste des petits ruminants virus by a polymerase chain reaction assay

A rapid and specific test was developed for the diagnosis of peste des petits ruminants disease. This assay is based on the rapid purification of RNA on glass beads followed by the reverse transcription-polymerase chain reaction (RT-PCR). To that effect, a set of primers (NP3/NP4) was used to amplify specifically a fragment of about 350 bp in the 3' end of the RNA messenger that encodes the nucleocapsid protein of the peste des petits ruminants virus. The PCR-product was detected by UV illumination after electrophoresis on agarose gel or by hybridisation with a digoxigenin-11-dUTP labelled oligonucleotide probe after a blot transfer. In comparison with the conventional titration technique on Vero cells, this RT-PCR assay was 1000-fold more sensitive. Compared with the popular Chomczynski and Sacchi's method [Anal. Biochem. 162 (1987) 156], the purification of the RNA on the glass beads offers the advantage of being more rapid and also avoiding the use of solvents.

Peste des petits ruminants has been widely present in southern India since, if not before, the late 1980s

Because previous authorities had suggested that small ruminants were playing a part in the dissemination of rinderpest, and a rinderpest-eradication campaign was about to begin, it was necessary to make precise virus identifications from a number of small-ruminant "rinderpest" outbreaks. When this was done using a database created from passive disease reports, we found that epidemics-reportedly due to rinderpest-were in fact due to peste des petits ruminants (PPRs). Although such cases had been common in India for a number of years, earlier clinical and laboratory reports no longer should be regarded as definitive. PPR outbreaks have been frequent in recent years. Further, we suggest that PPR is not a recent invader of India.

The matrix protein gene sequence analysis reveals close relationship between peste des petits ruminants virus (PPRV) and dolphin morbillivirus

The gene encoding the matrix protein of peste des petits ruminants virus (PPRV) has been cloned and its nucleotide sequence determined. This gene is 1466 nucleotides long and contains an open reading frame (ORF) capable of encoding a basic protein of 335 amino acid residues with a predicted molecular weight of 38,057 Da. This ORF starts at position 33-35 and ends with the codon TAA at position 1038-1040 thus leaving a long untranslated region (426 nucleotides) at the 3' end of the messenger RNA. This fragment is very G/C rich (68.5%) and in contrast to the ORF region appears to be least conserved in the M gene sequence of the morbilliviruses. A comparison of the PPRV M protein with those of other viruses in the group confirms the previously noted high degree of conservation for this protein sequence. The percent of identity within the group ranges from 76.7 to 86.9%, the highest being with the dolphin morbillivirus matrix protein.

Detection of peste des petits ruminants virus antigen in conjunctival smears of goats by indirect immunofluorescence

Peste des petits ruminants virus (PPRV) antigen was detected in conjunctival epithelial cells obtained from goats in the early or late stage of the disease by the use of a specific monoclonal antibody (mAb) to PPRV in an immunofluorescent antibody test (IFAT). The affected goats were sampled during an outbreak of peste des petits ruminants in Eritrea. Syncytia were also observed in some smears, consistent with a morbillivirus infection, but the IFAT was more sensitive than staining for syncytia in the detection of viral antigen, the two tests giving 63 per cent and 40 per cent of animals, respectively, with positive tests. Positive immunofluorescence was observed in samples from goats in the early and late stages of the disease, but was not observed with a specific rinderpest mAb or with conjunctival smears from uninfected animals. It is concluded that preparation of conjunctival smears for staining for syncytia is a simple procedure which can be applied in the field, and by use of a specific mAb PPRV infection can be rapidly confirmed and differentiated from rinderpest.

The isolation of peste des petits ruminants virus from northern India

The aetiological agent responsible for an epizootic of a rinderpest-like disease afflicting sheep and goats in three states of northern India was confirmed as peste des petits ruminants virus. To differentiate the virus from rinderpest a number of diagnostic tests were used, including immunocapture ELISA, specific oligonucleotide primers in a reverse transcriptase polymerase chain reaction, immunofluorescence with virus specific monoclonal antibodies and virus isolation. The virulence profile of one isolate in cattle sheep and goats was established. Infected animals developed specific antibody responses and excreted specific antigen in their lachrymal secretions.

Rinderpest virus infection of bovine peripheral blood monocytes

The ability of rinderpest virus (RPV) to replicate in vitro in adherent peripheral blood monocytes and monocyte-derived macrophages under non-stimulation conditions was investigated. When flow cytometry analysis on bovine peripheral blood mononuclear cells (PBMC) was performed, monocytic cells were seen to be targets for infection by the cell culture-attenuated RBOK vaccine strain of RPV. Viral glycoprotein (H) and nucleoprotein (N) expression in adherent blood monocytes and monocyte-derived macrophages was compared with the infection in Vero cells, in which a productive infection typical of morbilliviruses is obtained. In both cell types, the infection was m.o.i.-dependent, but the rate of viral protein accumulation was slower in monocytes/macrophages. Double-labelling experiments with monoclonal antibodies against RPV and the myeloid marker CD14 confirmed that the infected blood adherent cells were monocytes and macrophages. Productive infection of monocytes was confirmed by progeny virus titration. Permissiveness to infection was not dependent on macrophage differentiation: in vitro maturation of monocytes to macrophages before infection, did not increase the susceptibility of these cells to RPV infection. With the virulent Saudi RPV isolate, similar results were obtained, although the Saudi virus apparently had a higher rate of replication compared to the attenuated virus. These observations demonstrate clearly that bovine blood monocytes and monocyte-derived macrophages serve as hosts for a relatively slow but productive infection by rinderpest virus.

Recent developments in the diagnosis of rinderpest and peste des petits ruminants

Effective implementation of control measures for rinderpest and peste des petits ruminants requires that a proper and rapid diagnosis of the disease is made. Peste de petits ruminants (PPR) can be confused clinically with other infections such as pasteurellosis or contagious ecthyma. Rinderpest, in its classical form, is easy to identify clinically; however, mass vaccination in many countries and also the emergence of mild strains of the virus have made clinical diagnosis more difficult. Clinical observations for both diseases should always be confirmed by a laboratory. Diagnostic techniques used in the past were virus neutralization, agar gel immunodiffusion and virus isolation in cell culture, followed sometimes by reproducing the disease in susceptible animals. All these techniques are either time-consuming, labour intensive, insensitive, or expensive to perform. With the advent of hybridoma and molecular biological techniques, new reagents to assist diagnosis have become available and have led to the development of specific and rapid tests for the diagnosis of each disease. The present article reviews the diagnostic techniques currently available. An indirect ELISA was used successfully to evaluate the status of cattle following the Pan African Rinderpest Campaign. More recently competitive or blocking ELISAs have been developed based on monoclonal antibodies specific for the N or H proteins of the viruses, and which enable differential diagnosis between rinderpest and PPR. This is particularly important in sheep and goats, which may be infected with either virus. In future, improved standardization and reduced costs may be expected with the introduction of ELISAs based on purified antigens expressed in gene vector systems such as baculovirus. ELISA may also be adapted to antigen detection. Nucleic acid technology has also been applied to virus detection procedures. Hybridization probes showed a disappointing sensitivity for diagnostic applications, but more recently the polymerase chain reaction method has shown great promise, providing the potential of high sensitivity combined with specificity.

Development of a competitive ELISA for detecting antibodies to the peste des petits ruminants virus using a recombinant nucleoprotein

A competitive ELISA based on the reaction between a monoclonal antibody (mAb) and a recombinant nucleoprotein of the peste des petits ruminants virus (PPRV) was developed. This protein was obtained in large quantities from insect cells infected with a PPR nucleoprotein recombinant baculovirus (N-B). The competitive ELISA was compared with the virus neutralisation test (VNT) for detecting specific antibodies to PPRV in sheep and goats. The time consuming VNT is the only prescribed test that is capable of distinguishing between PPRV and the cross-reactive rinderpest virus (RPV). The competitive ELISA involves the simultaneous addition of the mAb and antibodies present in a positive serum, leading to competition for a specific epitope on the N-B. Optimum conditions were obtained by using serum samples which had positive or negative neutralising activity against PPRV or RPV. A negative cut-off point was determined on PPRV-negative sera from RPV-vaccinated cattle. A threshold value of 48 per cent inhibition, calculated from the mean for this population plus 2.7 standard deviations, was used in routine testing. A total of 683 sera were analysed by the competitive ELISA and the VNT. A good correlation (r = 0.94) was observed between the titres obtained in the two tests, with 80 sera that were from laboratory sources. The agreement between the two tests was determined on 271 field sera (kappa = 0.825). Their relative sensitivity (94.5 per cent) and specificity (99.4 per cent) were assessed on the 148 laboratory sera plus the 271 sera used for the determination of kappa.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of monoclonal antibodies in the diagnosis of contagious caprine pleuropneumonia (CCPP)

Contagious caprine pleuropneumonia is a severe disease affecting goats in Eastern Africa and the Middle East, caused by Mycoplasma sp. type F38. Its exact geographical distribution is however not exactly known due to the lack of specificity of the available serological tests and the difficulty in cultivating M. sp. F38. A panel of monoclonal antibodies (mAbs) was produced, using crude or membrane proteins antigens from type F38 strains to immunize mice. The reactivity of the mAbs was tested by an immunobinding assay with crude mycoplasma antigens spotted on nitrocellulose filters. One hundred and twelve antigens, standardized at 0.5 mg protein/ml, were used. Mycoplasma strains were chosen among closely related species of the "mycoides cluster", M. capricolum, Group 7 of Leach, M. mycoides mycoides LC, M. mycoides mycoides SC, M. mycoides capri, as well as among species that are isolated from goat lungs, M. arginini, M. ovipneumoniae, M. putrefaciens, M. agalactiae. Out of 60 mAbs, 4 were chosen to build an identification test for mycoplasmas of the "mycoides cluster". Controls showed that accurate identification could be hampered by antigenic heterogeneity within the M. capricolum species. One mAb was used for the direct detection of M. sp. F38 antigen in pleural fluid from goats suspected of CCPP. The sensitivity of the test can be estimated at 0.5 micrograms protein/ml. Comparison with isolation results show a 74% agreement between the two methods. The same mAb was used to build a blocking ELISA. This serological test was strictly specific for CCPP. It detects antibodies in sera of naturally infected or artificially immunized animals while it remained negative with hyperimmune sera to related strains such as PG 50. Direct antigen detection and blocking ELISA are tools that may enable a better assessment of CCPP distribution.

Rapid differential diagnosis of rinderpest and peste des petits ruminants using an immunocapture ELISA

An immunocapture ELISA for the diagnosis of rinderpest and peste des petits ruminants is described. Monoclonal antibodies directed against non-overlapping antigenic domains on the nucleocapsid (N) were used to detect the virus N protein in supernatants from infected cells and in field specimens. The assay, which is very sensitive, can be performed in one hour on pre-coated plates. There was no cross reaction between the two viruses in the test and the N protein could be detected in infected cell supernatants kept at ambient temperature for one week. These results show that the ELISA is suitable for routine diagnosis of field samples.

Field diagnostic kits: a solution for developing countries?

An exact assessment of the animal health situation in a country is an essential element in formulating eradication and control programmes, and in regulating international trade in animals and animal products from that country. Due to a lack of human and technical resources, Veterinary Services in developing countries often lack precise knowledge on disease occurrence. Since the collection and transmission of reliable information on animal diseases in developing countries are major concerns of the Office International des Epizooties (OIE), a project aimed at improving this situation was implemented with international financial support. This project involved the development by the Centre for the Application of Methodology for the Diagnosis of Animal Diseases (CAMDA) of field kits for the diagnosis of the main diseases present in tropical Africa: rinderpest, peste des petits ruminants (PPR), contagious bovine pleuropneumonia (CBPP) and contagious caprine pleuropneumonia (CCPP). Several tests already exist, such as complement deoxyribonucleic acid (cDNA)-specific probes and polymerase chain reaction (PCR) for rinderpest and PPR, DNA probes and PCR for CBPP, capture enzyme-linked immunosorbent assay, the agglutination test and the immunobinding peroxidase test for CCPP, etc. With specific reference to these examples, the various problems faced by the OIE and CAMDA are reviewed.

Monoclonal antibody-based blocking enzyme-linked immunosorbent assay for specific detection and titration of peste-des-petits-ruminants virus antibody in caprine and ovine sera

A blocking enzyme-linked immunosorbent assay (B-ELISA), using two neutralizing monoclonal antibodies (MAbs), was established and compared with the virus neutralization test (VNT) for detecting specific peste-des-petits-ruminants virus (PPRV) antibody in caprine and ovine sera. This technique was developed because VNT, the only available specific serological test for PPRV and the cross-reactive rinderpest virus (RPV), is time-consuming and unaffordable for most laboratories in regions where both peste des petits ruminants and rinderpest occur. The test depends on the blocking of the binding of the MAb to a specific epitope in the presence of positive serum. Test conditions were optimized by using peste-des-petits-ruminants and rinderpest sera that were known to be VNT positive and negative. A blocking format, in which serum is preincubated with a solid-phase PPRV antigen and then incubated with the MAb, yielded levels of sensitivity and specificity superior to those of a competitive format, in which the two reagents are added simultaneously. A threshold value of 45% inhibition, representing the mean for a negative population (n = 277) plus 2.7 standard deviations, was adopted for routine screening. A total of 605 serum samples were screened by B-ELISA and the VNT. The sensitivity and specificity of B-ELISA relative to the VNT were 90.4 and 98.9%, respectively. Of 264 field serum samples tested, 11 (4.2%) could not be assayed by the VNT because of contamination or cytotoxicity; the overall agreement quotient between results of the two tests (n = 253) was 0.91. A high correlation (r>/=0.98) was observed between B-ELISA and the VNT for endpoint titration of sera (n=57). Because B-ELISA proved to be nearlyas sensitive and specific as the VNT while being simpler and more rapid, it would be an adequate substitute for the VNT for assessing herd immune status and for epidemiologic surveillance.

A competitive ELISA using anti-N monoclonal antibodies for specific detection of rinderpest antibodies in cattle and small ruminants

A competitive ELISA (C-ELISA) using monoclonal antibodies (mAbs) which bind to the nucleo-protein (NP) of rinderpest virus (RPV) for detection of RPV antibodies in cattle and small ruminant sera is described. Unlike virus neutralisation test (VNT), this test using mAb IVB2-4, can detect specific RPV antibodies without showing a cross-reaction with antibodies to peste-des-petits ruminants-virus (PPRV); by contrast, when mAb VE4-1 is used the test detects both RPV and PPRV antibodies, including low levels of antibodies that can be found in sera containing maternal antibodies. Although antibodies to the PPRV 75-1 strain are also detected with mAb 51-5-6, the test is suitable for assessing the immune status of cattle against the Rinderpest Old Kabete (RBOK) strain. The results from a panel of sera with a known status of vaccination provide evidence for a highly significant correlation between C-ELISA and VNT. This test may be a useful tool for a standardized and accurate determination of the immunity status of both cattle and small ruminants.

Comparison of rinderpest and peste des petits ruminants viruses using anti-nucleoprotein monoclonal antibodies

Monoclonal antibodies (MAbs) were obtained using a purified preparation of the RBOK strain of a rinderpest vaccine virus. The cytoplasmic immunofluorescent staining test showed that these clones had specificity for the nucleoprotein (N) of the virus. Six clones which immunoprecipitated the N protein corroborated these results. Thirteen anti-N MAbs were used to compare geographically widespread rinderpest viruses (RPV) and peste des petits ruminants viruses (PPRV) to two other morbilliviruses, measles (MV) and canine distemper (CDV). The N protein antigen profiles of the 23 isolates determined by immunofluorescent staining and enzyme linked immunosorbent assay (ELISA) on infected cells enabled us to classify the strains into groups. A differential identification of the morbilliviruses can be made using one MAb or associations of the MAbs. The potential to distinguish between RPV and PPRV and between virulent and avirulent strains of rinderpest is of primary interest.

[An immunoenzyme test used for the detection of antibodies to rinderpest: the advantage of using a purified virus cultivated in a cell line]

Two types of in vitro assays (enzyme immunoassay and sero-neutralization test) were compared for their ability to detect antibodies to rinderpest virus in field sera from West African bovines. Purified virus grown on Vero cells (Ag/Vero) or bovine kidney cells (Ag/BK), were tested as antigen in enzyme-linked immunoassays (EIA). The results of the comparative evaluation of the two antigens by EIA, prove that Ag/Vero did enhance the sensitivity and the specificity of the test in comparison to Ag/BK and offers a 94% correspondence with seroneutralization.

Trypanosoma brucei: analysis of relapsing populations in sensitive and resistant breeds of cattle

The clone DiTat 1.1 of Trypanosoma brucei brucei was injected into four bovids, and clones obtained from successive waves of parasitemia were used to study the expressed variant-specific surface glycoprotein repertoire. Twenty-four clones were obtained which could be classified into 12 different variable antigen types, in addition to the clone injected, using agglutination or immunofluorescence with monospecific antisera. The variable surface glycoproteins of the 25 clones were extracted using the detergent octyl-beta-D-glucopyranoside in the presence of the protease inhibitor, N-cbz-L-phenylalaninechloromethylketone. The molecular weights varied from 52,000 to 69,000 and the pI from 5.0 to 8.8. The virulence of 14 clones representing 13 variable antigen types was ascertained in mice. The mean survival time ranged from 20.5 to 43.0 days. Clones isolated from early peaks of parasitemia in the bovid were the most virulent while clones derived from later peaks were less virulent. It seems that organisms of diminishing virulence appear in bovids, leading to self-cure of the disease. All clones were sensitive to human serum in a blood infectivity inhibition test. Antibody against all virulent clones appeared in 20 cattle (10 Zebus, 10 Baoulés) which had been injected with T. brucei DiTat 1.1. There was no evidence for parasites of high or low virulence being preferentially expressed in resistant or sensitive hosts.

Anti-trypanosome specific immune responses in bovids of differing susceptibility to African trypanosomiasis

A clone of Trypanosoma brucei brucei (DiTat 1.1) was injected into 32 bovids of various breeds, 11 animals being kept as controls. Five animals, Simmental-Ndama F1 crosses, were extremely sensitive. They showed overt symptoms and one died on day 18 of infection despite treatment with a trypanocidal drug. Seven other animals became ill but recovered progressively and cleared the infection. Twenty animals, of breeds generally considered to be trypanosensitive as well as ones from trypanotolerant breeds, did not show symptoms apart from anaemia and cleared the infection. Putative protective antibody, i.e. directed against exposed determinants on the coat variant-specific glycoprotein, was detected by agglutination, complement-mediated lysis and inhibition of infectivity. All animals showed a primary immune response consisting of IgM whose kinetics and amplitude were indistinguishable between animals of differing sensitivity. The response was long-lasting, whether the animals had been treated or not with a trypanocidal drug 3 weeks after infection, and antibody of IgG1 and IgG2 types were detected in certain sensitive as well as resistant animals after 2 months. Some animals were rechallenged with DiTat 1.1 either 1 year after the primary infection or 6 months after inoculation of irradiated trypanosomes. Peak titres of antibody were lower than was the case following primary infection but higher levels of mercaptoenthanol-resistant antibodies were seen. In no case was there any difference in the response of sensitive or tolerant animals. Our results do not support the idea that resistance of certain bovids to African trypanosomiasis is due to a better protective antibody response.