Adimasie, Balemual Abebaw: Prevalence, public health and socioeconomic importance of infectious diseases abortion in cattle in Africa 2007–2022
ABSTRACT
Abortion is the main cause of production loss in dairy husbandry systems and has a significant negative impact on the reproductive efficiency of dairy cows. In several African countries, especially in West and East Africa, the risk of zoonotic diseases is high. The causative agents of abortion in cattle include bacterial, viral, protozoans, and fungus.
Bovine viral diarrhea (BVD), Trichomonas fetus, Brucella abortus, and Aspergillus fumigatus are the most common, with high rates of abortion or persistent infection. The prevalence of brucellosis, leptospirosis, BVD, and Q fever in different African countries varies from 0%–40%, 1.1%–24%, 51%–77%, and 0.9%–28.2%, respectively, depending on the geographical location, and even higher if an outbreak case is suspected. The prevalence of abortions in Ethiopia ranges from 2.2%–28.9%. This difference in prevalence rates may be due to variations in cattle breeds, geographical locations, and husbandry management systems. According to studies carried out from 2010–2019, the brucellosis prevalence in cattle varied between 29.3% and 31.9% in South Sudan and 0.2%–21.9% in Kenya, whereas the prevalence of human brucellosis ranged from 23.3% to 33.3% in South Sudan and 0.6%–35.8% in Kenya. Abortion of cattle causes significant economic damage to cattle breeders. The loss can range from $500 to $900 per animal, depending on the stage of pregnancy, feed costs, milk loss, and replacement costs. Brucellosis remains the most common zoonotic disease worldwide, with more than 500,000 new cases diagnosed annually.
Rapid and accurate diagnosis of infectious abortion is helpful in decreasing the risk to humans and animals and in implementing appropriate prevention and control strategies. Appropriate therapy, vaccination, owner advice, and artificial insemination are useful for decreasing these diseases.
KEYWORDS Africa; cattle; economic impact; infectious disease; prevalence; public health
Introduction
Sub-Saharan African countries are characterized by a high burden of zoonotic diseases and poverty [ 1]. Ethiopia is the first east Africa country, which has the largest livestock population in Africa, with 70,291,776 cattle, of which 22,598,088 are dairy animals constituting 32.15% of the total cattle population [ 2]. In Africa, Livestock provides approximately 5.6% of the agricultural gross domestic product (GDP) and 16.5% of the national GDP. It also contributes 30% of agricultural employment, and 15% of export earnings [ 3]. However, reproductive health problems are becoming the major obstacles hindering this development plan [ 4]. Abortion is the most important condition that limits the ability of cows to produce calves and significantly reduces the profits of producers [ 5, 6]. Abortion is the removal of a dead fetus during the pregnancy of cattle between 42 and 260 days of pregnancy [ 7]. When a death occurs between 1 and 2 months of pregnancy, it is often called early embryonic death [ 8]. The highest risk of fetal death occurs in the first trimester of pregnancy, and gradually reduces as pregnancy progresses, and the risk increases slightly until the last month of pregnancy [ 9]. Reproductive diseases are the main cause of economic losses in animal husbandry [ 10]. Bovine abortions inflict serious economic damage on dairy farmers. The losses may range from $500 to $900 per animal, depending upon the stage of gestation, feed costs resulting in milk loss, and the value of replacement costs [ 11]. These can be attributed to the costs of treatment, repeat breeding, transmission of infectious agents, and abortions within the herd. It has been estimated that 90% of the losses are due to infectious pathogens. The frequency of abortions differs greatly based on the health condition of each herd [ 12, 8]. Abortions by cattle may cause significant public health problems. Thus, fast, and accurate diagnosis is essential to decrease the risk to humans and animals and to assess pathogens with zoonotic potential ( Brucella spp , Listeria spp, Leptospira spp, Q-fever, and Salmonella spp) [ 13, 1]. The prevalence of different pathogens was analyzed in 360 cows in Algeria and was found to range from 0% ( T. foetus) to 15% ( Neospora caninum) [ 14]. The prevalence of leptospirosis, Q fever, and brucellosis in different African countries ranged from 1.1%–24%, 0.9%–28.2%, and 0%–40%, respectively, depending on geographical location [ 1]. According to studies carried out in 2010–2019, brucellosis prevalence in cattle varied between 29.3% and 31.9% in South Sudan, and 0.2%–21.9% in Kenya, whereas the prevalence of human brucellosis ranged from 23.3% to 33.3% in South Sudan, and 0.6%–35.8% in Kenya [ 15]. A meta-analysis using random effects models were performed to calculate the pooled seroprevalence of brucellosis in Ethiopia. The estimated pooled seroprevalence of brucellosis was found to be 3.0% (95% CI: 2.0, 4.0) [ 16]. The prevalence rate of abortion in Ethiopia ranges from 2.2% to 28.9% as described in Table 1 [ 17]. This difference in prevalence rate may be due to variations in different associated risk factors, and husbandry management systems [ 18]. A recent study indicates that brucellosis is still a widespread disease, causing huge economic losses due to abortion [ 19]. Therefore, the objectives of this systematic review are:
- To describe the epidemiology of infectious abortion in bovine.
- To explain the public health effects of infectious abortions in dairy cattle.
- To address the economic significance of infectious abortions in cattle.
Table 1.Summary of the prevalence rate of abortion in dairy cattle in Ethiopia.
| Author |
Year |
Site |
Breed |
Prevalence (%) |
| Haftung and Gashaw |
2009 |
Bako |
Cross |
6.0 |
| Esheti and Moges |
2014 |
Debre Zeit |
Holstein and Borena cross |
5.3 |
| Haile et al. |
2010 |
Addis Ababa |
Cross |
5.9 |
| Dinka |
2013 |
Assella |
Local and Cross |
14.5 |
| Hadush et al. |
2013 |
Debre Zeit |
Cross |
6.7 |
| Regassa et al. |
2016 |
Mekelle city |
Local and Cross |
13.3 |
| Haile et al. |
2014 |
Hossana |
Local and Cross |
2.6 |
| Bitew and Prased |
2011 |
Bedelle |
Local and Cross |
13.9 |
| Degefa et al. |
2011 |
Arsi zone |
Local and Cross |
8.7 |
| Dawit and Ahmed |
2013 |
Kombolcha town |
Cross |
9.1 |
| Gizaw et al. |
2007 |
Nazareth town |
Local and Cross |
2.2 |
| Ararsa and Wubishet |
2014 |
Borena zone |
Borena |
12.2 |
| Enda and Moges |
2016 |
Wolaita Sodo |
Jersey and Cross |
4.8 |
| Ayana and Gudeta |
2015 |
Bako |
Horro and Cross |
5.9 |
| Mekonnin et al. |
2015 |
Mekelle |
Cross |
6.4 |
| Wagari and Shiferaw |
2016 |
Horro Guduru |
Horro and Cross |
4.4 |
| Siyoum et al. |
2016 |
Adea Berga |
Jersey |
28.9 |
Major Infectious Abortion in Bovine
Abortion is an important cause of production losses in the dairy industry and has a significant negative impact on the reproductive efficiency of dairy cows [ 21]. Several countries in Africa are at high risk of zoonotic diseases, because of intensive livestock animal rearing, poor health services, and agricultural activities [ 22]. There are several protozoal, viral, fungal, and bacterial causes of abortion [ 8, 23]. Infectious agent abortions are caused by bacterial, fungal, and viral causes, which account for 50%–65%, 20%–25%, and 15%–25% of cases, respectively [ 24]. Based on the abortion rate the major infectious abortion agents in cattle are Aspergillus fumigatus, Trichomonas fetus Brucella abortus, and Bovine viral diarrhea (BVD) virus [ 25].
Bacterial causes of abortion
Many bacteria result abortion in bovine with varieties of symptoms, times of abortion, and abortion rates, as explained in Table 2 [ 25, 26]. Table 2.Major bacterial causes of abortion and occurrence period.
| Disease and agents |
Clinical finding |
Pregnancy trimester of abortion |
Abortion rate |
Samples for diagnosis |
| Brucellosis (Brucella abortus) |
Ss Metritis, chronic infection |
Third trimester |
High, up to 90% in a susceptible herd |
placenta, fetus, or uterine discharge |
| Leptospirosis (Leptospira hardjo) |
Removal of fetus may occur at febrile stage. |
Abortion occur throughout gestation, late 6 month |
25%–30% |
Placenta, fetus |
| Campylobacter fetus |
Placenta: mild placentitis, hemorrhagic cotyledons |
5–8 months |
Rare abortion storms |
Placenta, foetal abomasal
contents, vaginal flushing |
| Listeriosis (Listeria monocytogens) |
Septicemia, Retained placenta and metritis. |
About 7 month |
Low, rare abortion storms |
Placenta, fetus |
| Arcanobacterium (Actinomyces pyogenes) |
Endometritis |
Any stage |
Rare abortion storms |
Placenta, fetus |
Epidemiology of brucellosis
The combined pooled prevalence of brucellosis in both Asian and African countries was 8% when compared to 12% in the Indian livestock population [ 27]. As reports indicated from 2010 and 2021 the prevalence rate was between 1.2% and 22.5% at the individual level and 3.3% and 68.6% at the herd level. However, the human brucellosis sero-prevalence rate was 2.15%–48.3% between 2006 and 2021 [ 28]. Brucellosis remains a major problem in the Mediterranean region, Latin America, and parts of Africa ( Fig. 1) [ 1]. It is caused by B. abortus. It has nine biotypes of B. abortus with several strains [ 29]. It is transmitted by contact on conjunctiva, ingestion, and penetration of intact skin [ 26]. Infections can occasionally acquire through placental contact, venereal contact, and inhalation [ 30].
Figure 1.
Livestock outbreak of brucellosis (abortus, melitenis, and suis). Source: World Animal Health Information Database, 2014 Data [ 1]. 
Pathogenesis: The pathogenesis of Brucella depends on its virulence and host susceptibility [ 31]. Once virulent Brucella are engulfed by macrophage, they enter different body lymph nodes. Inhibition of phagosome-lysosome function helps intracellular survival [ 21]. Superoxide dismutase and catalase production may play a role in bacterial resistance to oxidative killing. In pregnant cows, B. abortus multiplies in high numbers in the chorionic trophoblasts of the growing fetus [ 22]. Necrotized fetal membranes permit the transmission of the bacteria to the fetus. Chorionic and fetal colonization results in abortion during the last trimester of gestation [ 1]. In non-pregnant cow, colonization occurs in the udder [ 23]. Erythritol occurs naturally in the greatest concentration in the placental and fetal fluids, stimulate the growth of B. abortus [ 17]. Clinical signs: The cotyledons are yellow-gray in color, necrotic, and covered with thick brown exudates [ 16] with no visible lesions on gross post-mortem findings ( Fig. 2) [ 26]. Retention of the placenta and metritis are the main sequelae in infected cows. Epididymitis and orchitis occur in bull [ 24].
Figure 2.
Diagnosis: Samples include semen, milk, and blood, which are used for the diagnosis of brucellosis for the detection of antibodies [ 20]. Immunodiagnostic tests are used to detect different types of antibodies and vary in their sensitivity and specificity [ 27]. Blood sample can be tested by plate Agglutination rose Bengal plate, or card test, tube agglutination [ 16]. Isolation and identification of B. abortus or B. melintensis is confirmatory [ 26]. Identification criteria are isolates contain MZN positive, colonial appearance, rapid urease activity, bacterial cell agglutination with a high tittered antiserum, and biotyping using a test [ 32]. PCR-method is used for the detection of brucella in fluids and tissue [ 19]. Treatment and control: The treatment of patient animals is not practiced because of the maintenance of carrier animals, high cost, and treatment failure [ 16]. Treatment is not satisfactory because of the intracellular nature of the bacteria in different parts of the body [ 30]. Vaccination and quarantine is important as prevention and control strategies [ 4].
Viral Causes of Abortion
Several viruses cause abortion in cattle, as shown in Table 3 [ 26, 23]. BVD causes persistent infection in cattle [ 28]. Table 3.Common viral causes of abortions.
| Disease and agents |
Time of abortion |
Lesions |
Samples for diagnosis |
Diagnostic test |
| Bovine herpes virus1, IBR |
Fifth to the ninth month |
mummified Placenta: |
Placenta, fetus, serum
samples from the dam |
FA test, virus isolation histopathology |
| Blue tongue, Orbivirus |
Any trimester |
Fetus: autolyzed |
Placenta, fetus, serum
samples from the dam |
virus isolation, Fetal serology |
| BVD virus, pestivirus |
Any month, but commonly up to 4 month |
Retained placenta, no specific lesions. |
Placenta, fetus
spleen, dam serum |
Pathology, Fetal serology FA test on fetal tissue |
| EBA, Foothill abortion |
Last trimester |
No pre-expulsion postmortem autolysis of the aborted fetus |
Placenta, fetus, serum
samples from the dam |
Pathology |
Prevalence of BVD
Sero-prevalence of BVD was 39.5% (95% CI 25–56.1), 45.2% (95% CI 35.9–54.8), 49.9% (95% CI 25.5–74.3), and 21.6% (95% CI 0.5–56) for sub-Saharan Africa, South America, Middle East, and Asia respectively [ 32]. BVD caused by the BVD virus (BVDV). This virus is under pestivirus within the Flaviviridae and can pass the placenta and destroy the fetus [ 22]. BVD can result in fetal anomalies, early embryonic death, and abortion [ 1]. Pathogenesis: BVDV is excreted in different body secretions. Exposure of seronegative cows to BVDV prevent fertility. Placental localization usually at 35 days of pregnancy, results in fetal infection [ 15]. During the first 4 months of pregnancy. Fetuses infected by non-cytopathic strains between 18 and 125 days of pregnancy are seronegative during birth but gradually shed BVDV continuously [ 12]. Mucosal disease occur later in life from a superinfection with the cytopathic BVDV. Fetuses infected between 100 and 150 days of pregnancy, are assumed as congenitally infected, which develops teratogenic defects in the brain, skin, or bronchiole [ 1]. Fetuses that are infected after 150 days usually recover without dysplastic lesions [ 25]. Post-natal infection with non-cytopathic virus is asymptomatic [ 12]. Infection of seronegative pregnant cow before 120 days of pregnancy can contract BVD disease [ 28]. When the virus infects the fetus, it results in mummification, abortion or early fetal death [ 29]. Clinical and pathologic findings: The clinical and post-mortem findings of BVDV infection in cattle differ with age and gestation condition [ 25]. Fetus mortality occurs during the first trimester, and abortion can occur at any stage of pregnancy [ 26]. Diagnosis: Aborted fetuses have cerebellar hypoplasia, cerebral malformation and cataracts type of dysplastic lesion [ 28]. Mild non-suppurative placentitis, and non-suppurative vasculitis microscopic lesions are observed in the placenta or lymph nodes [ 17]. Viral antigen was detected by a fluorescent antibody test using samples from the kidneys or lung [ 12].
A tentative diagnosis can be made based on history and clinical signs. Viral antigen detection are possible using reverse transcription-PCR [ 28, 31].
Treatment and control
BVDV is prevented by vaccination, elimination of persistently infected cattle, and the introduction of new PI animals into the herd [ 4].
Protozoal Causes of Abortion
Protozoal diseases causing abortion are Trichomoniasis, Sarcocystosis, Neosporosis and Trichomoniasis [ 26]. Protozoal diseases that cause abortion in cattle at different rates and times are shown in Table 4. Table 4.Protozoal diseases causing abortion in bovine.
| Disease and cause |
Abortion rate |
Time of abortion |
Samples to collect |
Laboratory diagnosis |
Trichomonosis (Trichomonas
fetus) |
Moderate,
5%–30% |
At 5 month |
Uterine discharge,
placenta and fetal tissues |
Microscopic examination, Agglutination test and Serology. |
| Neosporosis (Neospora caninum) |
Sporadic outbreaks are common (20%–40%). |
At 3–8 months of pregnancy |
Dam sera and fetal fluids
Fixed placenta, brain, heart |
ELISA and IFAT |
| Babesia bovis and B. bigemina |
Rare |
All trimesters |
Dam whole blood and serum |
PCR detection in whole blood
ELISA or IFAT on serum |
Trichomoniasis
It is caused by T. fetus, which is a venereal transmitted and multi flagellated organism of the reproductive tract of bovine [ 28]. It induces infertility problem or early fetal death in pregnant cows [ 13]. Trichomonas fetus is found in the vagina, uterus, epididymis, vas deferens and macerated fetus [ 1]. The organism is pleomorphism, pear-shaped, varies from 10 to 25 µm in length, and has three anterior flagella [ 28]. When we observe T. fetus under microscope, it is motile and progresses by rolling jerky movements [ 16].
Pathogenesis
The organism inhibits the preputial cavity and transmission to the cow occurs during coitus [ 21]. The trichomonas reach the uterus via the cervix to cause low-grade endometritis. After time, organisms spread into the vagina, often 2 or 3 days before estrus [ 28]. This results in early abortion, and the organisms can be located in the allantoic fluid and amniotic fluid. Eventually dairy cattle develop a sterile immunity [ 31]. Abortion occurs before the fourth month of gestation [ 1]. Following abortion, there is a persistent uterine discharge, and purulent endometritis due to retained placenta [ 11]. In male cattle, a preputial discharge, small nodules on the preputial and penile membranes occur after infection [ 6].
Clinical signs and diagnosis
Early abortion and retained placenta are main clinical findings in cows. Purulent endometritis and pyometra leads cows to be permanently sterile [ 6]. Diagnosis is based on the observing the parasite under light microscope. Washing organisms from the stomach of the aborted fetus or the predilection site is the first procedure [ 1]. Preputial washings from the bull and vaginal mucus collection from the anterior end of the vagina by suction into a sterile tube help the examination under microscope for the presence of organisms [ 1]. For a herd examination, a sample of vaginal mucus may be examined for the presence of specific agglutinins against laboratory cultures of T. fetus [ 14].
Treatment and control
Treatment and sexual rest for 3 months are important for infected cows [ 15]. The bulls are treated with dimetridazole and culling is the best strategy [ 14].
Neospora caninum
The parasite has vertical and horizontal transmission from the dog to cow. The immune response in non-pregnant cows is mediated by inflammatory cytokines that induce growth inhibition, lysis, and cell death. This response play a role in inducing abortion in pregnant cows [ 22, 28]. Infection late in pregnancy in a naïve dam favors transmission without clinical effects, while mid-term infection leads to abortion [ 24]. In addition, thickened edematous placental membranes, mild autolysis of the fetus, and disseminated inflammatory and necrotic lesions are common [ 11].
Fungal Disease
Aspergillosis
Aspergillus spp, Mucor spp, Absida, or Rhizopus spp are an important causes of bovine sporadic abortion [ 18]. It is estimated that A. fumigatus is responsible for 90%–95% of the infections in cattle. The data were acquired from an environmental source [ 15].
Pathogenesis
Animals can acquire fungi through ingestion or inhalation, which then cross to the placenta. Pathological features include cotyledon enlargement and necrosis of intercotyledonary area [ 18].
Clinical sign and diagnosis
Necrosis of maternal cotyledon cause a soft, yellow, cushion-like structure [ 31]. Pneumonic lungs, fetal stomach contents, and granulomatous nodules were used as specimens [ 16]. Tissue scraping can be examined using direct microscopy after clearing in 10% KOH. Sabouraud dextrose agar is used for culturing and isolation of the fungus [ 26]. Aspergillus fumigatus has a white fluffy colony and then it returns to velvety or granular, and bright bluish-green [ 25].
Treatment and control
Ketoconazole, miconazole, and itraconazole has been used for the treatment of aspergillosis [ 32] . The prevention of hay and silage elimination has undergone noticeable deterioration [ 15].
Public health importance
The public health burden and socioeconomic effects of zoonotic diseases may vary according to the geographical location [ 13]. Brucella abortus, B. melitensis, and B. suis are highly pathogenic to humans. Brucellosis remains the most common zoonotic disease in the world, with more than 500,000 new cases reported annually [ 29]. Among the infectious agent that causes the removal of the fetus, Brucella spp, Listeria spp, and Salmonella spp have significant public health significance [ 22]. Brucellosis is often a neglected disease despite being endemic with high zoonotic potential in many countries[ 7]. The prevalence of human brucellosis differs between areas and has been reported to vary with standards of personal and environmental hygiene, animal husbandry practices, species of the causative agent, and local methods of food processing [ 25].
The most common signs and symptoms of human brucellosis are fever, asthenia, myalgia, arthralgia, sweats, lymphadenopathy, hepatomegaly, and splenomegaly [ 26]. Osteoarticular manifestations are the most common forms of localized disease [ 2]. Salmonellosis has an important global public health effect, because it is a food-borne disease [ 19]. Abortion, meningoencephalitis, and septicemia are clinical findings of Listeriosis [ 15]. Leptospirosis is a globally important zoonotic disease caused by the genus, Leptospira [ 27]. It occurs in the late summer and during rainy seasons in tropical regions [ 18]. It can be transmitted either by direct or indirect transmission [ 9, 17].
Economic Impact of Abortion in Bovine
Bovine brucellosis causes huge losses to the dairy industry; however, there is a dearth of comprehensive economic studies. Losses of 6%−10% of the income per animal were reported in Africa [ 3]. In Nigeria, losses were estimated at US $575, 605 per year. Brucellosis causes economic losses in cattle by resulting in decreased milk, infertility, and abortion [ 1]. The economic impact of abortion depends on the direct and indirect cost loss [ 28]. If we calculate the conception-to-conception interval, it is 173 days on average. On average, a cow takes 72 days to conceive after abortion [ 30]. Different values have been reported for the cost of abortion, ranging from $90 to $2333 based on different studies. These differences are caused by the stage of gestation in which the abortion occurs and by the differences in factors such as predicted cow performance, breeding and replacement decisions, feed and milk price, and the stage of lactation [ 17]. Estimates of the cost of an abortion to a producer range from $90 to $1900 depending on when pregnancy occurred and differences in predicted cow performance, prices, and breeding and replacement decisions [ 31].
Conclusion
Abortion is the main cause of production loss in the dairy industry and it has a significant negative impact on the reproductive efficiency of dairy cows. The risk of zoonotic diseases is high in many African countries, particularly in west and east Africa. The prevalence of brucellosis, leptospirosis, BVD, and Q fever in different African countries varies from 0%–40%, 1.1%–24%, 51%–77%, and 0.9%–28.2%, respectively, depending on the geographical location, and even higher if an outbreak cases are suspected. The prevalence of abortions in Ethiopia ranges from 2.2% to 28.9%. This difference in prevalence rates may be due to variations in cattle breeds, geographical locations, and husbandry management systems. Trichomoniasis, Neosporosis, Aspergillosis, Brucellosis, and BVD are the most significant infectious diseases. The abortion of dairy cattle has a significant economic impact on cattle breeders. Economic losses can range from $500 to $900 per animal, depending on the stage of gestation, feed costs, and milk loss. Salmonella, Brucella, and Listeria spp. significantly affect public health. Prevention by collecting samples for laboratory analysis, keeping biosecurity, and utilizing vaccination programs that inhibit the introduction and spread of infectious agents is mandatory. Therefore, the following recommendations are proposed.
- People working in cattle husbandry should address the risk of infectious diseases.
- Implementation of quarantine, vaccination, and elimination of persistently infected animals.
- Awareness creation to the community to use PPE and pasteurize or boil milk.
Availability of materials
The material set used in this review article is available from the corresponding author and can be accessed through reasonable request.
Competing interests
The author has declared that no competing interests exist.
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