Disease Surveillance: Monitoring livestock pregnancy loss
Systematically tracking and analysing reproductive loss in livestock helps with efforts to safeguard the health and productivity of food animals by identifying causes and high-risk areas.
- Department of Veterinary Medicine, Michael Okpara University of Agriculture, Nigeria
Raising healthy and disease-free livestock is globally important for ensuring food and economic security as well as public health. Information about the pathogens causing livestock diseases across Africa is lacking, which makes it difficult to design strategies to prevent and control such diseases across the continent. This difficulty – combined with heat stress due to extreme temperatures and humidity – reduces livestock productivity, such as growth or milk production (Janssens et al., 2020), and increases the likelihood of livestock diseases being transmitted to humans.
Livestock abortion – where a pregnancy ends early and the foetus is expelled – is distressing for both animals and farmers, and contributes to reduced productivity and profitability of livestock projects (Keshavarzi et al., 2020). Although there are multiple potential causes of abortion, several pathogens have been associated with it globally. Therefore, collecting and analyzing data on abortion rates and their timing and associated factors could help authorities detect deviations from baseline levels that signal infections or environmental stressors that warrant further investigation (Norzin et al., 2023). This would serve as a resource for prioritizing disease control strategies (Gachohi et al., 2024), allowing policymakers to allocate resources strategically, minimizing the economic burden on farmers and the broader agricultural industry.
Due to poor disease monitoring and lack of infrastructure in Africa, little is known about the causes and impacts of livestock abortions (Dórea and Vial, 2016). Data on livestock diseases in the region rarely include information on abortion cases (Thomas et al., 2022), making it difficult to launch interventions where they are most needed. Now, in eLife, Sarah Cleaveland (University of Glasgow) and colleagues from various institutes in Tanzania, the United Kingdom and New Zealand – including Felix Lankester (Washington State University) as first author – report results from a surveillance study in northern Tanzania that aimed to identify abortion-causing pathogens and their impact on animals raised for food (Lankester et al., 2024).
The research was conducted through collaboration with the Ministry of Livestock and Fisheries, and local government authorities across Tanzania. Farmers that engage in various agricultural practices – including raising livestock alone or combined with crop cultivation or sustainable farming methods (Bodenham et al., 2021) – were encouraged to report abortion cases to livestock field officers, who then reported to the researchers. If an abortion was reported within 72 hours of it occurring, appropriate samples were collected from the females (blood, milk and vaginal swab) and the aborted foetuses. Additionally, a questionnaire was used to gather history of the livestock management, and laboratory analysis was used to test for a range of microorganisms.
A total of 215 abortion cases in cattle, sheep and goats were investigated, revealing that abortions occurred more during the dry season and in exotic and cross-bred animals rather than local livestock breeds. In 19.5% of cases, abortion was attributed to identifiable pathogens, including some that cause mild to severe illness in humans (such as Brucella spp, Coxiella burnetii, Toxoplasma gondii and Rift Valley fever virus), as well as pathogens not transmissible to humans (Neospora spp and Pertivirus). The study also identified valuable information for designing future studies. Vaginal swabs from aborting animals proved more sensitive for detecting causative agents than swabs from foetuses and the placenta. Furthermore, the longer the delay between abortion and analysis of samples, the less likely the causative agent was to be identified.
The findings suggest that surveillance of livestock abortion can be used to track important disease-causing agents responsible for reproductive loss that are not easily identified through other forms of livestock disease surveillance. This valuable information also allows monitoring of diseases that can be transmitted to humans. Additionally, the observation that more abortions occurred in non-indigenous livestock than local breeds could be used to guide herd improvement programs, for example by introducing more local livestock.
One limitation of the work of Lankester et al. is that only ten different microorganisms were tested for. In the future, expanding this number may identify more causative agents. Furthermore, increasing the number of people involved in investigation and providing suitable transport for field officers could ensure abortion cases are reported and investigated more promptly (Nansikombi et al., 2023). With the knowledge provided by Lankester et al., establishing an effective reporting and investigation system could help to design disease control measures that would be implementable even in remote rural areas.
References
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Global hunger and climate change adaptation through international tradeNature Climate Change 10:829–835.https://doi.org/10.1038/s41558-020-0847-4
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Effect of abortion on milk production, health, and reproductive performance of Holstein dairy cattleAnimal Reproduction Science 217:106458.https://doi.org/10.1016/j.anireprosci.2020.106458
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Event-based surveillance: Providing early warning for communicable disease threatsCanada Communicable Disease Report 49:29–34.
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- Version of Record published: May 15, 2024 (version 1)
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Disease Surveillance: Monitoring livestock pregnancy loss
eLife 13:e98828.
https://doi.org/10.7554/eLife.98828
Further reading
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- Epidemiology and Global Health
Background:
The Zanzibar archipelago of Tanzania has become a low-transmission area for Plasmodium falciparum. Despite being considered an area of pre-elimination for years, achieving elimination has been difficult, likely due to a combination of imported infections from mainland Tanzania and continued local transmission.
Methods:
To shed light on these sources of transmission, we applied highly multiplexed genotyping utilizing molecular inversion probes to characterize the genetic relatedness of 282 P. falciparum isolates collected across Zanzibar and in Bagamoyo district on the coastal mainland from 2016 to 2018.
Results:
Overall, parasite populations on the coastal mainland and Zanzibar archipelago remain highly related. However, parasite isolates from Zanzibar exhibit population microstructure due to the rapid decay of parasite relatedness over very short distances. This, along with highly related pairs within shehias, suggests ongoing low-level local transmission. We also identified highly related parasites across shehias that reflect human mobility on the main island of Unguja and identified a cluster of highly related parasites, suggestive of an outbreak, in the Micheweni district on Pemba island. Parasites in asymptomatic infections demonstrated higher complexity of infection than those in symptomatic infections, but have similar core genomes.
Conclusions:
Our data support importation as a main source of genetic diversity and contribution to the parasite population in Zanzibar, but they also show local outbreak clusters where targeted interventions are essential to block local transmission. These results highlight the need for preventive measures against imported malaria and enhanced control measures in areas that remain receptive to malaria reemergence due to susceptible hosts and competent vectors.
Funding:
This research was funded by the National Institutes of Health, grants R01AI121558, R01AI137395, R01AI155730, F30AI143172, and K24AI134990. Funding was also contributed from the Swedish Research Council, Erling-Persson Family Foundation, and the Yang Fund. RV acknowledges funding from the MRC Centre for Global Infectious Disease Analysis (reference MR/R015600/1), jointly funded by the UK Medical Research Council (MRC) and the UK Foreign, Commonwealth & Development Office (FCDO), under the MRC/FCDO Concordat agreement and is also part of the EDCTP2 program supported by the European Union. RV also acknowledges funding by Community Jameel.
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- Epidemiology and Global Health
- Microbiology and Infectious Disease
Background: Few national-level studies have evaluated the impact of 'hybrid' immunity (vaccination coupled with recovery from infection) from the Omicron variants of SARS-CoV-2.
Methods: From May 2020 to December 2022, we conducted serial assessments (each of ~4000-9000 adults) examining SARS-CoV-2 antibodies within a mostly representative Canadian cohort drawn from a national online polling platform. Adults, most of whom were vaccinated, reported viral test-confirmed infections and mailed self-collected dried blood spots to a central lab. Samples underwent highly sensitive and specific antibody assays to spike and nucleocapsid protein antigens, the latter triggered only by infection. We estimated cumulative SARS-CoV-2 incidence prior to the Omicron period and during the BA.1/1.1 and BA.2/5 waves. We assessed changes in antibody levels and in age-specific active immunity levels.
Results: Spike levels were higher in infected than in uninfected adults, regardless of vaccination doses. Among adults vaccinated at least thrice and infected more than six months earlier, spike levels fell notably and continuously for the nine months post-vaccination. By contrast, among adults infected within six months, spike levels declined gradually. Declines were similar by sex, age group, and ethnicity. Recent vaccination attenuated declines in spike levels from older infections. In a convenience sample, spike antibody and cellular responses were correlated. Near the end of 2022, about 35% of adults above age 60 had their last vaccine dose more than six months ago, and about 25% remained uninfected. The cumulative incidence of SARS-CoV-2 infection rose from 13% (95% CI 11-14%) before omicron to 78% (76-80%) by December 2022, equating to 25 million infected adults cumulatively. However, the COVID-19 weekly death rate during the BA.2/5 waves was less than half of that during the BA.1/1.1 wave, implying a protective role for hybrid immunity.
Conclusions: Strategies to maintain population-level hybrid immunity require up-to-date vaccination coverage, including among those recovering from infection. Population-based, self-collected dried blood spots are a practicable biological surveillance platform.
Funding: Funding was provided by the COVID-19 Immunity Task Force, Canadian Institutes of Health Research, Pfizer Global Medical Grants, and St. Michael's Hospital Foundation. PJ and ACG are funded by the Canada Research Chairs Program.
