Congenital bovine epizootic arthrogryposis and hydranencephaly

Virus as Teratogenic Agents

Viral infectious diseases are important causes of reproductive disorders, as abortion, fetal mummification, embryonic mortality, stillbirth, and congenital abnormalities in animals and in humans. In this chapter, we provide an overview of some virus, as important agents in teratology.We begin by describing the Zika virus, whose infection in humans had a very significant impact in recent years and has been associated with major health problems worldwide. This virus is a teratogenic agent in humans and has been classified as a public health emergency of international concern (PHEIC).Then, some viruses associated with reproductive abnormalities on animals, which have a significant economic impact on livestock, are described, as bovine herpesvirus, bovine viral diarrhea virus, Schmallenberg virus, Akabane virus, and Aino virus.For all viruses mentioned in this chapter, the teratogenic effects and the congenital malformations associated with fetus and newborn are described, according to the most recent scientific publications.

The potential for bluetongue virus serotype 16 to cause disease in sheep in New South Wales, Australia

BLUETONGUE VIRUS SEROTYPE 16 DETECTION IN NSW: In coastal New South Wales (NSW), bluetongue virus (BTV) serotypes 1 and 21 are endemic and transmitted in most years without evidence of disease. However, serotype 16 (BTV-16) infection was detected for the first time in NSW in November 2016 in cattle undergoing testing for export. Retrospective testing of blood samples collected from sentinel cattle as part of the National Arbovirus Monitoring Program (NAMP) established that the first detected transmission of BTV-16 in NSW occurred in April 2016 in sentinel cattle on the NSW North Coast. Subsequently, until 2022, BTV-16 has been transmitted in most years and was the predominant serotype in the 2018-2019 transmission season. The data available suggests that BTV-16 may have become endemic in NSW. EXPERIMENTAL STUDIES: During experimental infection studies with BTV-16, all sheep were febrile, with the peak of viremia occurring 6-10 days after inoculation. There was nasal and oral hyperaemia in most sheep with several animals developing a nasal discharge and nasal oedema. All sheep developed coronitis of varying severity, with most also developing haemorrhages along the coronary band. There was a high incidence of haemorrhage in the pulmonary artery, epicardial petechiae, extensive pericardial haemorrhages and moderate body cavity effusions including pericardial effusions. CONCLUSION: Overall, experimental pathogenicity findings suggest moderate disease may occur in sheep in the field. These findings, when combined with climatic variability that could result in an expansion of the range of Culicoides brevitarsis into major sheep-producing areas of the state, suggest that there is an increasing risk of bluetongue disease in NSW.

Arbovirus infections of animals: congenital deformities, encephalitis, sudden death and blindness

Viruses from five different taxonomic families have been shown to be the cause of disease outbreaks in either domesticated or wild animals. These include viruses spread by both mosquitoes and biting midges from the genus Culicoides, especially C. brevitarsis. A number of arboviruses also present significant impediments to the international movement of live animals, semen and embryos.

Post-epidemic Schmallenberg virus circulation: parallel bovine serological and Culicoides virological surveillance studies in Ireland

Background

Schmallenberg virus (SBV) emerged in northern-Europe in 2011 resulting in an epidemic of ruminant abortions and congenital malformations throughout the continent. In the years following the epidemic there have been reports of SBV overwintering and continued circulation in several European countries. When the population-level of immunity declines in exposed regions, re-introduction of SBV could result in further outbreaks of Schmallenberg disease. The aims of this study were to determine the SBV seroprevalence in previously exposed Irish dairy herds in 2014 and to investigate if SBV continued to circulate in these herds in the three years (2013–2015) following the Irish Schmallenberg epidemic.

Whole-herd SBV serosurveillance was conducted in 26 herds before (spring) and following the 2014 vector-season (winter), and following the 2015 vector-season (winter). In spring 2014, 5,531 blood samples were collected from 4,070 cows and 1,461 heifers. In winter 2014, 2,483 blood samples were collected from 1,550 youngstock (8–10 months old) and a subsample (n = 933; 288 cows, 645 heifers) of the seronegative animals identified in the spring. Youngstock were resampled in winter 2015. Culicoides spp. were collected in 10 herds during the 2014 vector-season and analysed for SBV; a total of 138 pools (3,048 Culicoides) from 6 SBV vector species were tested for SBV RNA using real-time PCR.

Results

In spring 2014, animal-level seroprevalence was 62.5 % (cows = 84.7 %; heifers = 0.6 %). Within-herd seroprevalence ranged widely from 8.5 %–84.1 % in the 26 herds. In winter 2014, 22 animals (0.9 %; 10 cows, 5 heifers, 7 youngstock) originating in 17 herds (range 1–4 animals/herd) tested seropositive. In winter 2015 all youngstock, including the 7 seropositive animals in winter 2014, tested seronegative suggesting their initial positive result was due to persistence of maternal antibodies. All of the Culicoides pools examined tested negative for SBV-RNA.

Conclusions

SBV appears to have recirculated at a very low level in these herds during 2013 and 2014, while there was no evidence of SBV infection in naïve youngstock during 2015. A large population of naïve animals was identified and may be at risk of infection in future years should SBV re-emerge and recirculate as it has done in continental Europe.

Bluetongue virus serotype 8-associated congenital hydranencephaly in calves

Hydranencephaly, the almost complete absence of the cerebral parenchyma, induced by infection with modified live bluetongue virus (BTV) crossing the placenta has previously been reported in sheep and rarely in cattle in the USA and in South Africa. The current study describes 29 cases of hydranencephaly in bovine foetuses and 'dummy' calves up to 3 months of age in Belgium associated with natural BTV serotype 8 infection very early in gestation. Histological examination of the remaining cerebral parenchyma showed moderate to severe atrophy of the neural tissue. The lesions observed support the hypothesis of BTV-induced destruction of precursor cells. However, in several calves a slight infiltration of the walls of venules and arterioles with T lymphocytes (vasculitis) was observed as well, which seems to be responsible for at least some of the lesions. Bluetongue viral RNA was detected in 15 animals using a BTV-specific real-time RT-PCR with a much higher success rate in brain tissues compared with blood and spleen samples. Virus isolation in embryonated eggs was unsuccessful. In conclusion, hydranencephaly in calves can be associated with natural wild-type BTV-8 intra-uterine infection.

Pathology of the corpus luteum of cows

The corpus luteum (CL) is a transient endocrine organ which can manifest a number of pathologic conditions such as cysts, inflammation, adhesions, dysfunction and neoplasia. Luteal and follicular cysts are the most commonly encountered abnormalities and need to be distinguished from cysts within a normal CL. Inflammatory lesions are also frequently encountered and can be caused by viral, bacterial, or iatrogenic causes. If inflammation is severe, adhesions and subfertility/infertility can result. Luteal dysfunction is a broad classification of another pathologic condition encountered in the cow. Generally this results in abnormal production of progesterone or abnormal luteal lifespan resulting in infertility. Neoplasms are relatively rare in the CL but include both primary and metastatic tumors. Understanding the pathologic conditions that occur within the CL will allow a more accurate clinical assessment of these very dynamic endocrine structures.

Akabane and bovine ephemeral fever virus infections

Akabane and bovine ephemeral fever viruses are exotic to the American continent. Both viruses are spread by insect vectors, and each causes disease of varying severity in food-producing animals. However, there are few other similarities between the agents and the diseases that they cause. They do not share the same insect vectors, the mammalian host range is different, and the clinical manifestations of virus infection vary markedly. Akabane virus is a cause of severe congenital defects, but adult animals show no signs of infection. In contrast, bovine ephemeral fever virus causes a febrile illness affecting mainly mature animals. If introduced to North America, it is probable that there would be significant economic losses, at least until endemic virus transmission patterns were established. Subsequently, it is likely that there would be patterns of alternate disease outbreaks followed by interepidemic periods in which there is a minor clinical effect.

Akabane virus

Akabane virus, an arthropod-borne Bunyavirus, is the major cause of epizootics of congenital malformations in ruminants in Australia, Japan, Korea, and Israel, and is suspected to be a cause of sporadic outbreaks elsewhere. Blood-sucking insects, such as biting midges, transmit the virus horizontally to vertebrates. Climatic factors influence the seasonal activity and geographic range of the vector population and, therefore, occurrence of related disease. Inoculated ruminants seroconvert rapidly after a short subclinical viremia. Infection is of consequence only if ruminants are pregnant and not protected by adequate specific neutralizing antibodies. In naive pregnant animals, virus may spread hematogenously to replicate and persist in trophoblastic cells of placental cotyledons and subsequently invade the fetus. A distinct tropism for immature rapidly dividing cells of the fetal central nervous system and skeletal muscle results in direct virus-induced necrotizing encephalomyelitis and polymyositis. If fetuses survive, such injury may manifest as arthrogryposis, hydranencephaly, porencephaly, microencephaly, hydrocephalus, or encephalomyelitis at term. The earlier in gestation that fetal infection occurs, the more severe the lesions, reflecting the large population of vulnerable cells and lack of fetal immunocompetency at earlier stages of pregnancy. Injury during the period of critical cell migration and differentiation in organogenesis may substantially disrupt structural development in target organs. Late gestational infections cause nonsuppurative inflammation in the brain and spinal cord, premature birth, or fetal death with stillbirth or abortion. Affected neonates are nonviable. Control is by vaccination but is not always justified economically. Akabane viral infections must be differentiated from infections with other teratogenic viruses (including related Bunyaviruses), inherited conditions, and maternal intoxications. Diagnosis is made by serology and viral isolation.

An outbreak of Akabane virus-induced abnormalities in calves after agistment in an endemic region

During 1988, 2 farmers in the Bega district agisted pregnant cattle in the Hunter Valley of New South Wales. On return to the district to calve, 54% of calves from herd 1 and 30% of calves from herd 2 were affected with congenital arthrogryposis or hydranencephaly caused by Akabane virus infection. Field observations and laboratory findings from this outbreak are presented, illustrating the danger of moving immunologically naive animals into areas where Akabane virus is endemic.

Future challenges of disease in the beef cattle industry

Disease control must be part of the management system in any beef cattle enterprise where improved net returns are a constant goal. A current view of the importance of disease is reflected in the research portfolio of the Australian Meat and Live-stock Research and Development Corporation (AMLRDC), where only 14% of projects relate to cattle health problems. Our relative freedom from epidemics is partly responsible for this balance, but the profession should continue to be alert to the range of actual or potential threats to the national herds and those predisposing factors, both managerial and environmental, that influence their effects. In Australia with its crucial beef export component, several priority areas can be identified. They are (i) completion of the Brucellosis and Tuberculosis Eradication Campaign (BTEC) (ii) improved knowledge of the effects of production of subclinical disease including deficiency states (iii) better understanding of the infertility complex from conception to birth. Congenital viral infections such as mucosal disease and the arbovirus group are slowly emerging from their epidemiological obscurity (iv) constant awareness of the potential threat of exotic diseases and defensive methods available to meet them. There is a particular need to understand the epidemiology of the large tropical cattle herd, which interfaces with South-East Asia. Our comparative freedom from epidemics should not cause any relaxation of vigilance by the veterinary services in the private or public sectors. Nor should government be allowed to minimise the critical role of the veterinary profession in our defense against animal disease (v) increased liaison with our trading partners in livestock exports.(ABSTRACT TRUNCATED AT 250 WORDS)

Akabane epizootics in New South Wales: evidence for long-distance dispersal of the biting midge Culicoides brevitarsis

In 1983 an outbreak of Akabane disease occurred in calves in New South Wales between Coolah and Dunedoo at the foothills of the Liverpool Range, from Molong to Oberon in the Blue Mountains and in the Bylong Valley. These areas, at the time of infection of the dams, were in a drought and conditions were unsuitable for the multiplication of C. brevitarsis. In late March meteorological phenomena developed producing air movements favourable for transporting infected midges from the Hunter Valley. A re-examination of the data from the epizootics of 1974 and 1955 showed that similar weather systems had developed. It is possible that the source of infected midges in these epizootics was also the Hunter Valley.

Congenital defects of the bovine central nervous system

Congenital brain defects in cattle are usually obvious at birth, but detection may depend on the nature and extent of the defect. The cause may be genetic or environmental, or the cause may be unknown. Many central nervous system defects are inherited as a simple autosomal recessive trait and may have a significant economic impact on purebred and commercial cattle operations. A common structural defect of genetic nature is internal hydrocephalus. A functional defect of simple autosomal recessive inheritance is bovine progressive degenerative myeloencephalopathy. The most significant teratogenic agents causing central nervous system defects are prenatal viral infections such as bovine virus diarrhea and bluetongue viruses. Many other defects of the central nervous system are reviewed.

Akabane disease in cattle: congenital abnormalities caused by viral infection. Spontaneous disease

Akabane disease, an infectious disorder causing congenital abnormalities in calves, was studied in naturally affected calves between 1972 and 1974 in Japan. The animals included one three-month fetus from which a strain of Akabane virus (OBE-1) was isolated, and a total of 177 stillborn or premature fetuses and deformed or infirm newborn calves that died within a few days of birth. The three-month fetus had nonpurulent encephalomyelitis in the undifferentiated central nervous system, characterized by necrosis of the nerve tissue and endothelial proliferation in the encephalitic process; and polymyositis in the myotubule phase with parenchymal degeneration and cellular infiltrates in the skeletal muscle. The full-term fetuses and newborn calves had nonpurulent encephalomyelitis in the early stage of the epizootic. In the middle to late stages, a dysplastic muscular change which we call runt-muscle disease was seen simultaneously with a decrease in number of ventral horn neurons in the spinal cord and arthrogryposis in the legs. Cystic cavities and thick vascular walls sometimes were seen in the central nervous system in these stages. Hydranencephaly was prominent in the late stage.

Teratogens associated with congenital contractures in humans and in animals

An evaluation of over 350 patients in a study of congenital contractures of the joints (arthrogryposis) included a review of family, pregnancy, and delivery histories for teratogenic exposures. Fifteen out of the total 350 patients studied had a possible teratogenic exposure: an infectious agent (viral or bacterial), maternal drug or toxin ingestion, chronic maternal neurologic or muscular illness, or a direct physical insult such as a structural uterine anomaly. Literature was reviewed for all human and animal cases reported with congenital contractures of the joints with an associated teratogenic insult. Those findings are discussed here.