Ibaraki disease in cattle

Ibaraki disease in cattle

Y KITANO

Introduction

Ibaraki disease is an acute Culicoides-borne orbiviral disease of cattle characterized by stomatitis and, in severe cases, difficulty in swallowing due to degenerative and necrotic changes in the musculature of the oesophagus, pharynx and/or tongue. It was first recognized in Japan in the late summer and autumn of 1959 and 1960, when it caused severe economic losses to cattle farmers. The causative agent was named after the prefecture of Ibaraki, in which the virus was first isolated from affected cattle.14 At that time, however, because the physicochemical and biological properties of Ibaraki virus were very similar to those of bluetongue virus (BTV) it was referred to as ‘bluetongue-like virus’ and ‘Kaeishi virus’, the latter because the first investigators were from the Japanese National Institute of Animal Health or ‘Kaeishi’ in Japanese. The disease was also known as laryngopharyngeal paralysis because of the characteristic clinical signs.14, 27 The virus is not pathogenic for sheep.14, 17, 21, 28

Aetiology

Ibaraki virus is a member of the epizootic haemorrhagic disease of deer (EHD) serogroup (see Epizootic haemorrhagic disease of deer), genus Orbivirus of the family Reoviridae. 8 It is a typical orbivirus (Figures 103.1 and 103.2). At present, Ibaraki virus is classified as serotype 7 in the epizootic haemorrhagic disease of deer virus (EHDV) serogroup.9 It has, however, been suggested that Ibaraki virus should be classified as serotype 2 of the nine serotypes based on neutralization tests with isolates from North America, Japan, Nigeria and Australia. However, there is a 27 per cent sequence divergence between the L2 gene of Ibaraki virus and the EHDV serotype 2 isolates of North America (which show only a 3 per cent divergence among themselves).5, 6, 11, 25

Ibaraki virus causes cytopathic effects in primary cell cultures of bovine,29 sheep and hamster kidney origin. It also replicates in cell cultures of BHK21-W11 of baby hamster kidney origin,15 HmLu-1 of suckling hamster lung origin, and mouse fibroblastic L cells, but not in primary cultures of horse and porcine kidney cells nor in HeLa cell cultures.When Ibaraki virus is injected into the yolk sac of chicken embryos, viral growth is as rapid in four-day-old embryos incubated at 33,5 °C as it is in those incubated at 37 °C. The virus also multiplies in the brain of suckling mice infected intracerebrally.30

The physicochemical properties of Ibaraki virus closely resemble those of BTV,21 but the neutralization, haemagglutination, complement fixation, and ferritin-tagging tests reveal that the two viruses possess different antigens.3, 4, 14, 27, 28 The agar gel precipitin and indirect fluorescent antibody tests show a two-way cross relationship between Ibaraki virus and EHDV serotypes 1 (New Jersey strain) and 2 (Alberta strain).4, 35

Ibaraki virus grown in HmLu-1 cell cultures haemagglutinates a wide variety of erythrocytes including bovine, goat, sheep, horse and rabbit, a property shared with other orbiviruses, such as African horsesickness (AHS) virus and BTV.3638

Epidemiology

Ibaraki disease was first recognized in the southern and central parts of Japan from August to December 1959, when it affected 30 076 cattle and caused 4 023 deaths. In 1960 a similar outbreak occurred from the end of September to December, involving parts of the Chubu and Kinki districts in the central part of Japan. In this outbreak a total of 4 717 cases were reported.14, 27, 28

Since the first outbreaks of Ibaraki disease in Japan no cases were recorded until 1982 and 1987 when further outbreaks occurred. In both of these outbreaks stillbirths and abortions were also reported.18

In the summer and autumn of 1997, many clinically affected cattle were observed on Kyushu Island, to the west of Japan. During the same period many pregnant cows aborted or had stillbirths. The serum of affected cows and some of the foetuses contained antibody against Ibaraki virus, and virus was isolated from some of the foetuses although the isolates differed genetically from strains isolated previously.39

Figure 103.1 Budding of Ibaraki viruses from cultured HmLu-1 cells. Bar = 100 nm

Figure 103.2 Mature Ibaraki viruses and the mass of tubular structures observed in cultured HmLu-1 cells. Bar = 200 nm

Serological surveys conducted from 1972 to 1975 to determine the possible involvement of arbovirus infections in the occurrence of congenital abnormalities in cattle in Japan, revealed that 16,4 per cent of the samples contained antibody against Ibaraki virus.22

Outside Japan, 73 cases of Ibaraki disease occurred in Korea in 1982.1 The disease has not been reported from any other country despite the fact that cattle with neutralizing antibodies against Ibaraki virus have been found in Taiwan, Australia,14, 27 Trinidad, Tobago, Guyana,12 and the Bali islands of Indonesia.23 Both in Australia and the tropical parts of the Americas,13 while disease has not been reported, different serotypes of EHDV, including Ibaraki virus, have been isolated from wild-caught Culicoides spp.8, 9, 33 and sentinel32 or affected cattle, and antibodies against the viruses detected.2, 7, 26

One of the epidemiological features of Ibaraki disease is its seasonal prevalence particularly during the late summer and autumn months and hence the possibility...

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