A pinboard by
Catherine Herzog

PhD Candidate, Pennsylvania State University


Using models to describe PPRV spread in Tanzania could better inform eradication efforts

To gain a better understanding of disease, scientists often use mathematical models to describe to describe how the virus or bacteria in question spreads. However, creating useful models faces many challenges. For livestock diseases, linking models to field data and applying these models correctly across scales in resource poor settings continue to be major challenges. When developed correctly, such models can be valuable to inform the design of successful eradication campaigns.

One important livestock disease currently being studied is peste des petits ruminants virus (PPRV), which primarily affects sheep and goats. The virus is spread by direct contact with infected hosts, droplets in the air, or other infected objects in the environment. PPRV causes high levels of illness and death in sheep and goats. Additionally, PPRV can infect cattle and wildlife, though symptoms may not be visible.

PPRV has recently expanded its geographic range, especially in resource poor settings. Currently, PPRV has spread to more than 70 countries in Asia, the Middle East, and Africa. PPRV threatens 80% of the nearly 2 billion sheep and goats raised globally. According to the FAO, over 330 million farmers’ livelihoods rely directly on sheep and goats and the demand for meat and milk is expected to rise 137-177% by 2030.

Our team is working on PPRV in Tanzania, where PPRV was first reported in 2008 in northern districts. In those areas, 45.8% of sheep and goats had antibodies to PPRV. PPRV then spread south, following the trade of infected animals. While a few outbreak studies of PPRV in Tanzania such as these have been reported, there have been no large, randomized serosurveys or modeling studies of PPRV transmission in Tanzanian livestock. Our team’s research seeks to describe PPRV epidemiology in northern Tanzanian sheep, goats, and cattle through a large serosurvey. Furthermore, our team will develop mathematical models to characterize herd demographic composition and disease transmission in order to describe the spread of PPRV among hosts in the system. This improved understanding of PPRV transmission dynamics will help inform upcoming PPRV eradication efforts.


Partial genetic characterization of peste des petits ruminants virus from goats in northern and eastern Tanzania.

Abstract: Peste des petits ruminants (PPR) is an acute viral disease of small ruminants. The disease was first reported in Tanzania in 2008 when it was confined to the Northern Zone districts bordering Kenya. The present study was carried out to confirm the presence of PPR virus (PPRV) in Tanzania and to establish their phylogenetic relationships. Samples (oculonasal swabs, tissues and whole blood) were obtained from live goats with clinical presentation suggestive of PPR and goats that died naturally in Ngorongoro (Northern Tanzania) and Mvomero (Eastern Tanzania) districts. The clinical signs observed in goats suspected with PPR included fever, dullness, diarrhea, lacrimation, matting of eye lids, purulent oculonasal discharges, cutaneous nodules, erosions on the soft palate and gums and labored breathing. Post mortem findings included pneumonia, congestion of the intestines, and hemorrhages in lymph nodes associated with the respiratory and gastrointestinal systems. PPRV was detected in 21 out of 71 tested animals using primers targeting the nucleoprotein (N) gene. Phylogenetic analysis, based on the N gene, indicated that PPRV obtained from Northern and Eastern Tanzania clustered with PPRV strains of Lineage III, together with PPRV from Sudan and Ethiopia. The findings of this study indicate that there are active PPRV infections in Northern and Eastern Tanzania, suggesting risks for potential spread of PPR in the rest of Tanzania.

Pub.: 20 Aug '14, Pinned: 20 Aug '17

Prevalence and distribution of Peste des petits ruminants virus antibodies in various districts of Tanzania.

Abstract: Despite the widespread prevalence of infection with Peste des petits ruminants virus (PPRV) in goats and sheep industry in Asia and sub-Saharan Africa, there have been few, if any, structured population-based studies examining the epidemiology of this infection in Tanzania. In this study, we investigated the seroprevalence, and risk factors, of Peste des petitis ruminants(PPR) in sheep and goat flocks from seven different geographical administration authorities (Ngorongoro, Monduli, Longido, Karatu, Mbulu, Siha and Simanjiro) located in Northern Tanzania. Serum samples from 657 and 892 sheep and goats, respectively, corresponding to 91 sheep/goat flocks and 43 villages were collected. Competitive enzyme linked immunosorbent assay (c-ELISA) was used to detect the presence of antibodies in the serum against PPRV. Chi-square analysis and multivariable logistic regression model were used to identify risk factors for PPRV seropositivity. Findings suggested that the sero-positive cases were significantly higher in goats than in sheep (49.5% versus 39.8%; P=0.002). The overall seroprevalence of PPRV infection in small ruminants was 45.8%. Highest seroprevalence (42.6-88.02%) was observed in Mbulu, Siha, Longido, Ngorongoro districts, while antibodies less than 40% to none were found in serum from Monduli, Karatu and Simanjiro, respectively. These findings confirm natural transmission of PPRV under field condition for the first time in Tanzania. Results may be correlated with variations in the sheep and goat husbandry practices within different geographic localities, the uncontrolled movement of animals, the levels of natural immunity and the sharing of grazing field amongst agro and pastoralists.

Pub.: 26 Aug '09, Pinned: 20 Aug '17

Genomic analysis of host - Peste des petits ruminants vaccine viral transcriptome uncovers transcription factors modulating immune regulatory pathways.

Abstract: Peste des petits ruminants (PPR), is an acute transboundary viral disease of economic importance, affecting goats and sheep. Mass vaccination programs around the world resulted in the decline of PPR outbreaks. Sungri 96 is a live attenuated vaccine, widely used in Northern India against PPR. This vaccine virus, isolated from goat works efficiently both in sheep and goat. Global gene expression changes under PPR vaccine virus infection are not yet well defined. Therefore, in this study we investigated the host-vaccine virus interactions by infecting the peripheral blood mononuclear cells isolated from goat with PPRV (Sungri 96 vaccine virus), to quantify the global changes in the transcriptomic signature by RNA-sequencing. Viral genome of Sungri 96 vaccine virus was assembled from the PPRV infected transcriptome confirming the infection and demonstrating the feasibility of building a complete non-host genome from the blood transcriptome. Comparison of infected transcriptome with control transcriptome revealed 985 differentially expressed genes. Functional analysis showed enrichment of immune regulatory pathways under PPRV infection. Key genes involved in immune system regulation, spliceosomal and apoptotic pathways were identified to be dysregulated. Network analysis revealed that the protein - protein interaction network among differentially expressed genes is significantly disrupted in infected state. Several genes encoding TFs that govern immune regulatory pathways were identified to co-regulate the differentially expressed genes. These data provide insights into the host - PPRV vaccine virus interactome for the first time. Our findings suggested dysregulation of immune regulatory pathways and genes encoding Transcription Factors (TFs) that govern these pathways in response to viral infection.

Pub.: 02 Apr '15, Pinned: 20 Aug '17

Sero-epidemiology of Peste des petits ruminants virus infection in Turkana County, Kenya.

Abstract: Peste des petits ruminants (PPR) is a contagious viral disease of small ruminants. Serum samples from sheep (n = 431) and goats (n = 538) of all ages were collected in a cross-sectional study in Turkana County, Kenya. The objective was to estimate the sero-prevalence of PPR virus (PPRV) infection and associated risk factors in both species. PPRV competitive enzyme-linked immuno-sorbent assay (c-ELISA) analysed the presence of antibodies in the samples. All analyses were conducted for each species separately. Multivariable logistic regression models were fitted to the data to assess the relationship between the risk factors and PPRV sero-positivity. Mixed-effect models using an administrative sub-location as a random effect were also fitted to adjust for possible clustering of PPRV sero-positivity. Intra-cluster correlation coefficients (ρ) that described the degree of similarity among sero-positive responses for each species in each of the six administrative divisions were estimated.Goats had a significantly higher sero-prevalence of 40% [95% confidence interval (CI): 36%, 44%] compared to sheep with 32% [95% CI: 27%, 36%] (P = 0.008). Combined sero-prevalence estimates were heterogeneous across administrative divisions (n = 6) (range 22% to 65%) and even more across sub-locations (n = 46) (range 0% to 78%). Assuming that PPRV antibodies are protective of infection, a large pool of PPRV susceptible middle age group (>6 months and < 24 months) in both species was estimated. This was based on the low sero-prevalence in this group in goats (14% [95% CI: 10%, 20%]) and in sheep (18% [95% CI: 13%, 25%]). Regression analysis returned significant risk factors across species: in sheep - vaccination status, age and administrative division; in goats - sex, age, administrative division and sex*age interaction. The intra-sub-location correlation coefficients varied widely across divisions (range <0.001 to 0.42) and across species within divisions.Biological, spatial and socio-ecological factors are hypothesized as possible explanations for variation in PPRV sero-positivity in the Turkana pastoral ecosystem.

Pub.: 19 Apr '15, Pinned: 20 Aug '17

Evaluating the role of vaccine to combat peste des petits ruminants outbreaks in endemic disease situation.

Abstract: Among the main intimidation to the sheep and goat population, PPR outbreaks are causing huge losses especially in endemic areas. During recent times, six outbreaks of PPR were confirmed at semi-organized goat farms/herds in various regions of Punjab province and Islamabad capital territory (ICT), Pakistan. The disease started after introduction of new animals at these farms with no history of previous PPR vaccination. The clinical signs appeared affecting respiratory and enteric systems and spread quickly. Disease caused mortality of 10-20% and morbidity of 20-40% within a time period of four weeks. Morbidity and mortality rates were 30.38% (86/283) and 15.55% (44/283), respectively. Three treatment regimes were executed to demonstrate the role of vaccination during outbreak at these farms. First was to use only the broad spectrum antibiotics (Penicillin & Streptomycin and/ or Trimethoprim and Sulfadiazine) at two farms (Texilla and Attock). Second treatment regime was to use the same broad spectrum antibiotic along with extensive fluid therapy (Farms at ICT-1 and ICT-2). The third regime was to use of broad spectrum antibiotic plus fluid therapy along with vaccinating the herd against PPR during first week of outbreak (ICT-3 and ICT-4). The third scheme of treatment gave the better results as there was no mortality in third week post-outbreak. Therefore, it is suggested to give proper importance to PPR vaccination along with conventional symptomatic treatment when dealing the PPR outbreaks in endemic disease conditions.

Pub.: 21 Aug '15, Pinned: 20 Aug '17

Economic losses associated with Peste des petits ruminants in Turkana County Kenya

Abstract: Peste des petits ruminants is a major economic disease affecting the pastoral herders in Kenya, with outbreaks in Turkana County having devastating effects on the Turkana livelihoods. Turkana County is a region associated with natural and manmade disasters, poor infrastructure and insecurity. There is limited essential data on livestock diseases and economic analysis. This study has attempted to estimate the direct economic loses occasioned by outbreaks of Peste des petits ruminants (PPR) based on perceived loss of benefits experienced by the Turkana people. Parameters for the analytical model were derived from secondary data, informal interviews and focused group discussions using participatory epidemiology methods. Results shows that losses due to PPR were estimated at US$ 19.1 million and mortality of small stock due to PPR constituted the greatest economic loss valued at US$ 16.8 million being 88% of the total losses. Other losses due to lost milk and weight loss constitute approximately 12% of the total losses. PPR has serious economic impacts on pastoral livelihoods, and previous estimation of PPR losses in Kenya was grossly undervalued. This study strengthens the basis for developing a system for the economic assessment of livestock diseases in areas with scanty data based on parameters derived from participatory epidemiology approaches for use in the mathematical model.

Pub.: 13 Apr '15, Pinned: 20 Aug '17

The global eradication of peste des petits ruminants (PPR) within 15 years-is this a pipe dream?

Abstract: Gordon Scott did much to inspire the eradication of rinderpest, probably the most outstanding veterinary achievement of the twentieth century, and one currently inspiring is the proposed eradication of peste des petits ruminants (PPR), a disease of sheep and goats caused by a closely related Morbillivirus. The evolution and geographic spread of PPR along with its epidemiological characteristics are discussed and related to ways in which its spread can be reduced through the provision of diagnostic aids to sanitary livestock movement at local level. Taking a historical look at rinderpest eradication, it was shown that much could be achieved using a legislation-backed zoosanitary approach or, once developed, the build up of herd immunities in isolated populations. As the final cap to this (circa), two hundred-year-long process, major national and internationally funded vaccination programmes falling within the informal coordinatorship of the OIE and FAO showed that final eradication could be achieved with remarkable rapidity if the seat of infection was known and if appropriate national and international interventions were aimed at ending virus transmission. Were such international cooperation to be forthcoming once more, the understanding, tools and experiences now on offer suggest that PPR could be controlled and eradicated far more rapidly than rinderpest.

Pub.: 08 Feb '16, Pinned: 20 Aug '17

The Economic Impact of Eradicating Peste des Petits Ruminants: A Benefit-Cost Analysis.

Abstract: Peste des petits ruminants (PPR) is an important cause of mortality and production loss among sheep and goats in the developing world. Despite control efforts in a number of countries, it has continued to spread across Africa and Asia, placing an increasing burden on the livelihoods of livestock keepers and on veterinary resources in affected countries. Given the similarities between PPR and rinderpest, and the lessons learned from the successful global eradication of rinderpest, the eradication of PPR seems appealing, both eliminating an important disease and improving the livelihoods of the poor in developing countries. We conducted a benefit-cost analysis to examine the economic returns from a proposed programme for the global eradication of PPR. Based on our knowledge and experience, we developed the eradication strategy and estimated its costs. The benefits of the programme were determined from (i) the averted mortality costs, based on an analysis of the literature, (ii) the downstream impact of reduced mortality using a social accounting matrix, and (iii) the avoided control costs based on current levels of vaccination. The results of the benefit-cost analysis suggest strong economic returns from PPR eradication. Based on a 15-year programme with total discounted costs of US$2.26 billion, we estimate discounted benefits of US$76.5 billion, yielding a net benefit of US$74.2 billion. This suggests a benefit cost ratio of 33.8, and an internal rate of return (IRR) of 199%. As PPR mortality rates are highly variable in different populations, we conducted a sensitivity analysis based on lower and higher mortality scenarios. All the scenarios examined indicate that investment in PPR eradication would be highly beneficial economically. Furthermore, removing one of the major constraints to small ruminant production would be of considerable benefit to many of the most vulnerable communities in Africa and Asia.

Pub.: 24 Feb '16, Pinned: 20 Aug '17

Co‐circulation of Peste‐des‐Petits‐Ruminants Virus Asian lineage IV with Lineage II in Nigeria

Abstract: Peste‐des‐petits‐ruminants (PPR), a major small ruminant transboundary animal disease, is endemic in Nigeria. Strains of the causal agent, peste‐des‐petits‐ruminants virus (PPRV), have been differentiated into four genetically distinct lineages based on the partial sequence of the virus nucleoprotein (N) or fusion (F) genes. Peste‐des‐petits‐ruminants virus strains that were identified initially in Africa were grouped into lineages I, II and III and viruses from Asia were classified as lineage IV and referred to as the Asian lineage. Many recent reports indicate that the Asian lineage is now also present in Africa. With this in mind, this study was conducted to reassess the epidemiology of PPRV in Nigeria. A total of 140 clinical samples from 16 sheep and 63 goats with symptoms suggestive of PPR were collected from different states of Nigeria during a four‐year period (2010–2013). They were analysed by the amplification of fragments of the N gene. Results for 33 (42%) animals were positive. The phylogenetic analysis of the N gene sequences with those available in GenBank showed that viruses that were detected belong to both lineage II and IV. Based on an analysis of the N gene sequences, the lineage IV isolates grouped into two clades, one being predominant in the north‐eastern part of the country and the other found primarily in the southern regions of the country. This study reports the presence of PPRV Asian lineage IV in Nigeria for the first time.

Pub.: 12 Jun '15, Pinned: 20 Aug '17

Serological Detection of Antibodies to Peste des Petits Ruminants Virus in Large Ruminants

Abstract: Peste des petits ruminants (PPR) is an economically important disease of small ruminants with a rapidly expanding geographical distribution. Peste des petits ruminants virus may manifest in a variety of ways with disease ranging from acute to subclinical. We investigated the exposure of large ruminants to PPRV in areas where the virus is endemic in the small ruminant population by assessing the serological status of groups of animals. This study focused on the Punjab province of Pakistan as an area where the virus is endemic and where mixed farming practices occur enabling close interactions between small and large ruminant populations. An overall PPR seropositivity was detected in 10.0% of cattle and 14.16% of buffaloes. Following an assessment of serological profiles in large ruminants within different age groups, a maximum seroprevalence was observed in cattle (17.5%) and buffaloes (22.5%) over 2 years of age indicating the potential utility of sampling large ruminant populations for PPR serosurveillance. The large ruminants sampled between one and two years of age had similar levels of seropositivity within populations with 11.2% and 16.2% of animals being seropositive, respectively. Current PPR vaccination strategies do not enable the differentiation between infected and vaccinated small ruminants, and as such, the serological surveillance of sheep and goats is of little value. When considering eradication programmes for PPRV, this factor is of great significance. However, where large and small ruminants are farmed together, serological surveillance of large ruminants may provide a snapshot of virus infection within populations where mild disease is present or where small ruminants are regularly vaccinated.

Pub.: 22 Jul '15, Pinned: 20 Aug '17

Peste Des Petits Ruminants in Benin: Persistence of a Single Virus Genotype in the Country for Over 42 Years

Abstract: Peste des petits ruminants (PPR) is a contagious and often fatal disease affecting sheep and goats. Currently, it is endemic in Africa, the Middle and Near East, the Indian subcontinent and China. Understanding the molecular epidemiology and evolution of PPR virus (PPRV) can assist in the control of the transboundary spread of this economically important disease. We isolated PPRV from pathological and swab samples collected 42 years apart (1969 and 2011) in Benin, West Africa, and sequenced the full genome of two isolates (Benin/B1/1969 and Benin/10/2011). Phylogenetic analysis showed that all of the characterized isolates clustered within viral lineage II and that the 2011 isolates fell into two distinct subgroups. Comparison of the full genome sequences revealed a 95.3% identity at the nucleotide level, while at the protein level, the matrix protein was the most conserved between the two viruses with an identity of 99.7% and only one amino acid substitution over the 42‐year sampling period. An analysis of specific amino acid residues of known or putative function did not identify any significant changes between the two viruses. A molecular clock analysis of complete PPRV genomes revealed that the lineage II viruses sampled here arose in the early 1960s and that these viruses have likely persisted in Benin since this time.

Pub.: 22 Jan '16, Pinned: 20 Aug '17

Eradication of Transboundary Animal Diseases: Can the Rinderpest Success Story be Repeated?

Abstract: A matrix system was developed to aid in the evaluation of the technical amenability to eradication, through mass vaccination, of transboundary animal diseases (TADs). The system involved evaluation of three basic criteria – disease management efficiency, surveillance and epidemiological factors – each in turn comprised of a number of elements (17 in all). On that basis, 25 TADs that have occurred or do occur in southern Africa and for which vaccines are available, in addition to rinderpest (incorporated as a yardstick because it has been eradicated worldwide), were ranked. Cluster analysis was also applied using the same criteria to the 26 diseases, creating division into three groups. One cluster contained only diseases transmitted by arthropods (e.g. African horse sickness and Rift Valley fever) and considered difficult to eradicate because technologies for managing parasitic arthropods on a large scale are unavailable, while a second cluster contained diseases that have been widely considered to be eradicable [rinderpest, canine rabies, the Eurasian serotypes of foot and mouth disease virus (O, A, C & Asia 1) and peste des petits ruminants] as well classical swine fever, Newcastle disease and lumpy skin disease. The third cluster contained all the other TADs evaluated with the implication that these constitute TADs that would be more difficult to eradicate. However, it is acknowledged that the scores assigned in the course of this study may be biased. The point is that the system proposed offers an objective method for assessment of the technical eradicability of TADs; the rankings and groupings derived during this study are less important than the provision of a systematic approach for further development and evaluation.

Pub.: 23 Jun '15, Pinned: 20 Aug '17

The first report of peste des petits ruminants (PPR) in camels (Camelus dromedarius) in Iran

Abstract: In mid-July 2013, an outbreak of peste des petits ruminants (PPR) was observed in a herd of camels after they were imported from Kuwait to the Khuzestan province in southwest of Iran. The clinical signs of the affected animals included sudden death, fever, oral erosion, and ecthyma like lesions, yellowish diarrhea, pneumonia and respiratory distress, enlargement of lymph node, severe dehydration, dermatitis, ulcerative keratitis, and conjunctivitis. Necropsy findings included keratoconjunctivitis, congestion and consolidation of the lung, paleness of the liver, and enlargement and edema of lymph nodes. Histopathological exam revealed degeneration and acute hyperemia of the lungs, fatty change and necrotic foci in the liver, tubular necrosis in the kidneys, and necrotic dermatitis. We used immunocapture enzyme linked immunosorbent assay (ELISA) to confirm peste des petits ruminants virus (PPRV) and differentiate it from rinderpest virus. Then virus genome was studied by molecular analysis for detecting of strain and substrain of the virus. Immunocapture ELISA of all specimens reacted positively against PPRV antigens. Also, reverse transcription polymerase chain reaction (RT-PCR) results in the lung and lymph nodes of the dead camels consolidated the cause of disease to be PPRV. The present study is the first report of the PPRV outbreak in camels in Iran.

Pub.: 08 May '16, Pinned: 20 Aug '17

The Opportunity To Eradicate Peste des Petits Ruminants.

Abstract: Peste des petits ruminants (PPR) is a highly infectious disease of sheep and goats that is caused by PPR virus, a member of the genus Morbillivirus that includes the viruses that cause rinderpest (RP) in cattle. RP was the first animal disease to be globally eradicated in 2011 and is only the second disease, after smallpox, to have ever been eradicated. PPR is one of the principal constraints to small ruminant production in Africa, Asia, and the Middle East. The epidemiology of PPR and RP as well as the technologies available for their diagnosis and control are similar. The conditions that favored the eradication of RP are also largely present for PPR. In this work, we outline the evolving strategy for eradication in light of current opportunities and challenges, as well as the lessons from other eradication programs in animal and human health. The global PPR situation and technology for its control are summarized. A strategy based on the lessons from previous eradication efforts that integrate epidemiology, social science, and economics as tools to target and motivate vaccination is summarized. Major aspects of the cost and benefit-cost analysis of the indicated program are presented. The overall undiscounted cost of eradication was estimated as $3.1 billion, and the benefit-cost ratio for the most likely scenario was estimated at 33.8. We close with a discussion of the possible next steps.

Pub.: 18 May '16, Pinned: 20 Aug '17