Infectious diseases causing bovine abortion and fetal loss

Listeriosis Outbreak in South Africa: A Comparative Analysis with Previously Reported Cases Worldwide

Listeria species are Gram-positive, rod-shaped, facultative anaerobic bacteria, which do not produce endospores. The genus, Listeria, currently comprises 17 characterised species of which only two (L. monocytogenes and L. ivanovii) are known to be pathogenic to humans. Food products and related processing environments are commonly contaminated with pathogenic species. Outbreaks and sporadic cases of human infections resulted in considerable economic loss. South Africa witnessed the world's largest listeriosis outbreak, characterised by a progressive increase in cases of the disease from January 2017 to July 2018. Of the 1060 laboratory-confirmed cases of listeriosis reported by the National Institute of Communicable Diseases (NICD), 216 deaths were recorded. Epidemiological investigations indicated that ready-to-eat processed meat products from a food production facility contaminated with L. monocytogenes was responsible for the outbreak. Multilocus sequence typing (MLST) revealed that a large proportion (91%) of the isolates from patients were sequence type 6 (ST6). Recent studies revealed a recurrent occurrence of small outbreaks of listeriosis with more severe side-effects in humans. This review provides a comparative analysis of a recently reported and most severe outbreak of listeriosis in South Africa, with those previously encountered in other countries worldwide. The review focuses on the transmission of the pathogen, clinical symptoms of the disease and its pathogenicity. The review also focuses on the major outbreaks of listeriosis reported in different parts of the world, sources of contamination, morbidity, and mortality rates as well as cost implications. Based on data generated during the outbreak of the disease in South Africa, listeriosis was added to the South African list of mandatory notifiable medical conditions. Surveillance systems were strengthened in the South African food chain in order to assist in preventing and facilitating early detection of both sporadic cases and outbreaks of infections caused by these pathogens in humans.

Evaluation of the potential effects of abortion on the productive performance of Iranian Holstein dairy cows

Calving records from the Animal Breeding Center of Iran collected from January 1983 to December 2007 and comprising 1,163,594 Holstein calving events from 2552 herds were used to evaluate the potential effect of abortion occurrence on 305-day milk yield, milk fat yield, fat percentage of milk and milk protein yield in Iranian Holsteins. Statistical analyses of production traits were performed using a linear mixed model procedure. Normal-calved cows had greater 305-day milk production, fat yield and protein yield of milk than abortive-calved cows (P < 0.05). However, abortive-calved cows had the greater milk fat percentage than normal calved cows (P < 0.05). The linear and quadratic effects of age of dam were significant on all of the studied traits (P < 0.05). The results of regression analysis showed that increase in the quadratic effect of age can cause an increase in the fat percentage of milk for all calvings including normal and abortive calvings. Because abortion is one of the most important conditions that limit a cow's ability to produce, maintaining the general health of cattle is important in minimizing the risk of abortion problems.

Infectious causes of embryonic and fetal mortality

The purpose of this review is to summarize bacterial, fungal, protozoan, and viral causes of reproductive dysgenesis in cattle, sheep, goats, pigs, horses, dogs, and cats. The clinical presentations of disease due to reproductive pathogens are emphasized, with a focus on assisting development of complete lists of causes that result in abortion and infertility in these species. Clinicians are encouraged to assess clinical presentation, create complete lists of differential diagnoses, obtain appropriate diagnostic samples, maximize diagnostic laboratory support, and avoid zoonotic infections resulting from reproductive pathogens of animals. The foundation of an accurate diagnosis of reproductive loss due to infectious pathogens facilitates the prudent use of immunization and biosecurity to minimize reproductive losses.

Infectious causes of bovine abortion during mid- to late-gestation

The accurate and prompt diagnosis of infectious abortions in a herd requires cooperation between the herd veterinarian and a veterinary diagnostic laboratory; working together, with good communication and appropriate sampling and testing, the chances of obtaining an etiologic diagnosis are improved. Abortion diagnosis is a challenge as a cause is usually identified in less than half of submitted fetuses. The majority of diagnosed abortions are attributed to infections by a moderate number of bacterial, viral, fungal and protozoal agents. The pathology and other findings used in the laboratory diagnosis of the major infectious agents causing bovine abortion in mid- to late-gestation will be discussed.

Predicting the probability of abortion in dairy cows: a hierarchical Bayesian logistic-survival model using sequential pregnancy data

Although abortion contributes substantially to poor reproductive health of dairy herds, little is known about the predictability of abortion based on age, previous abortion or gravidity (number of previous pregnancies). A poor understanding of effects of maternal factors on abortion risk exists, in part, because of methodological difficulties related to non-independence of multiple pregnancies of the same cow in analysis of fetal survival data. We prospectively examined sequential pregnancies to investigate relationships between fetal survival and putative dam risk factors for 2991 abortions from 24,706 pregnancies of 13,145 cows in nine California dairy herds. Relative risks and predicted probabilities of abortion (PPA) were estimated using a previously described hierarchical Bayesian logistic-survival model generalized to incorporate longitudinal data of multiple pregnancies from a single cow. The PPA increased with increasing dam age at conception, with increasing number of previous abortions, and if the previous pregnancy was aborted >60 days in gestation. The PPA decreased with increasing gravidity and with increasing number of days open. For cows that aborted, the median time to fetal death decreased slightly as gravidity increased. The study considers several methodological issues faced in epidemiologic investigations of fetal health, including multi-modal hazard functions, extensive censoring and non-independence of multiple pregnancies. The model improves our ability to predict bovine abortion and to characterize fetal survival, which have important applications to herd health management.

Evaluation of factors that affect embryonic loss in dairy cattle

OBJECTIVE

To identify potential risk factors for embryonic loss before 35 to 42 days of gestation in dairy cattle.

DESIGN

Prospective observational study.

ANIMALS

381 cows.

PROCEDURE

Body condition score was determined at the time of artificial insemination (AI; day 0) and on days 20, 23, and 27 and between days 35 and 41; serum progesterone concentration was measured on days 0; 20 or 21; and 23, 24, or 25. Cows were excluded from analyses if day 0 serum progesterone concentration was > or = 1.0 ng/mL and classified as pregnant on day 23 if serum progesterone was > 1.5 ng/mL on day 20 or 21 and day 23, 24, or 25. Cows were examined via transrectal ultrasonography on day 27 or 28 and rectally palpated for pregnancy on days 35 to 41.

RESULTS

39% of cows that were pregnant on day 23 lost their embryo by day 27, and 18% of cows that were pregnant on day 27 or 28 were not pregnant on days 35 to 41. Breeding a pregnant cow posed the greatest risk for embryonic loss at both time periods. Mean serum progesterone concentrations on day 21 or 22 and day 23, 24, or 25 were lowest for cows that lost an embryo between days 24 and 28. Cows with a linear somatic cell count score > 4.5 before AI were twice as likely to lose the embryo by 35 to 41 days, compared with cows with a score < 4.5.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that embryonic loss could be reduced by more accurate estrus detection, reducing mastitis, and strategies to improve progesterone concentration after breeding.

Biosecurity for reproductive diseases

Application of rational principles of risk management in designing an effective biosecurity plan for reproductive diseases can be an important part of a profitable operation. Knowledge of the disease status of the particular herd, the effective strategies for disease exclusion including test performance and reservoirs is necessary. Vaccination can be an effective part of a biosecurity program by increasing herd immunity and decreasing the impact of an outbreak, but by itself will not prevent infections and losses. A more comprehensive approach to disease control is needed. Development and implementation of a biosecurity program is an individualized effort undertaken for a particular operation. Knowledge of the disease status of the herd for each agent of concern and prioritization of the diseases most important in the herd is necessary. The biosecurity plan is then specific for the herd and the particular agent(s) of concern. Practitioners can apply knowledge of the epidemiology and ecology of disease agents to identify and implement logical control points for the individual herd. Many control strategies may be effective for more than one disease. A comprehensive look at the operation is necessary to make sure that the cost of the biosecurity plan does not exceed the return in prevented disease and increased production over the planning period.

Serological study of the frequency of leptospiral infections among dairy cows in farms with suboptimal reproductive efficiency in Galicia, Spain

Between March 1996 and September 1997, 15 farms located in Galicia (NW Spain) and experiencing suboptimal reproductive efficiency were visited and blood samples were obtained from all the lactating cows (n=442). Additionally, 1060 samples were obtained monthly from a cohort of 219 lactating cows belonging to nine of the farms between March 1996 and April 1997. All the samples were tested by microscopic agglutination (MAT) using live antigens representing the following Leptospira interrogans serogroups: Australis, Autumnalis, Ballum, Canicola, Grippotyphosa, Icterohaemorrhagiae, Louisiana, Pomona, Sejroe, Shermani and Tarassovi. Eighty-one of the 442 cows were positive against one or more serogroups (P=18.33%). Serologically, L. bratislava and L. grippotyphosa were detected as the most prevalent serovars (P=7.92 and 7.69%, respectively) and as the serovars against which the probability of seroconversion was highest (P=0.27 and 0.25, for a 12-month period, respectively) among those studied. The proportional hazards regression method was used for evaluating the seasonal trend of seroconversions against these two serovars. The risk of seroconversion against L. grippotyphosa was significantly higher during spring. The risk of seroconversion against L. bratislava did not differ significantly among seasons. Our results suggest that infections by L. bratislava did not follow, among the study animals and during the study period, the pattern typically described for non-adapted serovars, pointing out the possibility that some strains of this serovar could behave as adapted serovars.

The frequency of endemic fetal loss in dairy cattle: A review

Estimates of the frequency of endemic fetal loss range from 0.4 to 10.6%, a 26-fold difference, in 26 studies of dairy herds over 5 decades. Sources of this difference include breed, geographic, study population, case definition and procedural differences. The definition of fetal loss was inconsistent among the studies and was often not clearly stated. Twelve of the studies cited only visually observed losses, while the remainder reported losses of all known pregnancies but using different gestational at-risk periods. Definitions of the resulting frequency measure and methods of computation varied widely among the studies. Fetal loss frequencies have been reported as ratios, proportions, incidence rates and cumulative incidence rates. Denominators used in frequency calculations have included the number of pregnant cows, number of cows in the breeding herd, number of cows that calved before or after the risk period and number of calves born. These procedural differences make comparisons among studies and an overall estimate of an expected frequency of endemic fetal loss in dairy cattle difficult at best. Procedural and definition differences aside, the median frequency of fetal loss from studies enumerating only observed abortions was 1.95% and from the studies that included both observed and unobserved abortions 6.5%. Based on this difference, approximately only 30% of endemic fetal losses are observed visually.

Experimental reproduction of bovine fetal Neospora infection and death with a bovine Neospora isolate

Studies were conducted to determine the pathogenic potential of the recently isolated bovine Neospora protozoa (BPA-1) for the bovine fetus. Cows chosen for study had Neospora titers < 160 using an indirect immunofluorescent antibody (IFA) test. Four experimental groups were studied. In group 1, 2 fetuses were inoculated in utero at 118 days gestation with culture-derived Neospora tachyzoites. A pregnant control cow was housed in the same pen, observed daily and screened serologically for evidence of exposure to Neospora. In group 2, 2 cows were infected with Neospora tachyzoites at 138 or 161 days gestation, and 1 control cow was given uninfected cell culture suspension simultaneously at 154 days gestation. Groups 3 (85 days gestation) and 4 (120 days gestation) each consisted of 2 cows infected with Neospora tachyzoites and 1 control cow given uninfected material at the same stage of gestation. Dead fetuses were surgically removed from the infected cows in group 1 on postinfection day (PID) 17. The histopathology was compatible with protozoal fetal infection, and protozoa were identified by immunohistochemistry. Viable fetuses were removed surgically from cows in group 2 on PID 28-30. The histopathology was compatible with protozoal fetal infection, protozoa were identified by immunoperoxidase techniques, and Neospora tachyzoites were reisolated in vitro from tissues of the 2 infected fetuses. In groups 3 and 4, the control fetus and 1 infected fetus were removed surgically between PID 26 and PID 33. The remaining infected cows were observed until fetal death or abortion occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigating perinatal calf mortality in beef herds

This article summarizes the information presented in this issue to identify the reasons for a perinatal calf mortality (PCM) problem through a risk-factor-evaluation approach. The benefits of necropsies in PCM investigations are discussed, and the gross lesions of the major causes of PCM are described. The use of 2 x 2 tables to calculate odds ratios and the Chi-square method to test the validity of the odds ratios are presented as methods to determine suspected risk factors. The article concludes with a discussion of the management plan used to solve a PCM problem.