Studies on Getah virus: some biological, physicochemical and antigenic properties of the MI-110 strain

Isolation and pathogenicity of a highly virulent group III porcine Getah virus in China

Introduction

Getah virus (GETV) is a multi-host virus found in pigs, horses, and blue foxes. Clinically, GETV can cause fever, diarrhea, and reproductive disorders in pigs, representing significant threats to pig breeding. At present, few studies have examined the pathogenicity of GETV in pigs of different ages.

Methods

In the present study, a new strain, named GETV-QJ, was isolated from clinically ill pigs, and whole genome sequencing analysis was performed. Besides the pathogenicity of piglets and pregnant sows of this strain was further studied.

Results

the results illustrated that the strain belonged to group III. The strain had 93.6%-96.3% homology with other subtypes, and its homology with the same subtype strain ranged 96.5%-99%. Further studies on the pathogenicity of the virus indicated that this strain caused severe diarrhea, fever, and intestinal and lung damage in 7-day-old piglets, resulting in their death. The piglet survival rate was 0%. In pregnant sows, this strain did not cause fever, death, or abortion, but it induced viremia, which affected the farrowing performance of sows and led to reduced piglet survival.

Discussion

In this study, we isolated a highly virulent group III and comprehensively established a pathogenic model of GETV in piglets and sows, providing a reference and guidance for the prevention and control of this infection.

Getah virus as an equine pathogen

Getah virus is a member of the genus Alphavirus in the family Togaviridae and has been frequently isolated from mosquitoes. Seroepizootiologic studies indicate that the virus is mosquito-borne and widespread, ranging from Eurasia to southeast and far eastern Asia, the Pacific islands, and Australasia. The natural host animal of the virus was not known until the first recognized occurrence of Getah virus infection among racehorses in two training centers in Japan in 1978. Outbreaks of clinical disease due to Getah virus infection occur infrequently, and only one outbreak has been reported outside Japan; this was in India in 1990. Clinical signs of the disease are mild and nonlife-threatening and are characterized by pyrexia, edema of the hind limbs, swelling of the submandibular lymph nodes, and urticarial rash, as reported in the 1978 epizootic. The morbidity was 37.9% (722 of 1903 horses) in one training center, with 96% of 722 affected horses making a full clinical recovery within a week without any significant sequelae. Antibodies against Getah virus were detected in 61.2% (172 of 281) and 55.8% (254 of 455) of horses at two training centers, respectively. Virus isolation can be attempted in VERO, RK-13, BHK-21, and many other cell lines as well as in suckling mouse brain. Blood plasma collected from suspect cases of infection at the onset of pyrexia is the specimen of choice. A diagnosis of Getah virus infection can also be confirmed serologically based on testing acute and convalescent phase sera by using SN, CF, HI, and ELISA tests. An inactivated vaccine is available for the prevention and control of Getah virus infection in horses in Japan.

Pathogenicity for horses of original Sagiyama virus, a member of the Getah virus group

Sagiyama virus is a member of the Getah virus group. Its pathogenicity for horses was examined. All the horses infected with the original 4 strains of Sagiyama virus (M6/Mag 33, Mag 121, Mag 132 and Mag 258) developed pyrexia ranging from 39.0 to 40.0 degrees C. Other clinical signs, characterized by eruptions, edema in the hind legs, enlargement of the submandibular lymph node and mild leukopenia, were also manifested. Viremia occurred 1-4 days post-inoculation (p.i.). Virus was recovered from spleen, liver, lung and various lymph nodes of a horse autopsied on Day 4 p.i. The maximum titer of virus (10(6.0) TCID50 g-1) was detected in the inguinal lymph node. Seroconversion was demonstrated in all the infected horses on Day 5 p.i. These clinical signs and virological findings were similar to those of horses infected naturally. The results indicate that Sagiyama virus has pathogenicity for horses and is similar to that of Getah virus.