1977
335
NEW ZEALAND VETERINARY JOURNAL
Some recent virus isolations and their importance in New Zealandt G.
w. Horner*
N.Z. \·er.J.25:335-36
INTRODUCTION
Today I am going to talk about some of the animal viruses which have been isolated recently in New Zealand and, along the way, I will make a few comments on the possible clinical significance of these various viruses. Veterinary virology is still in its infancy in New Zealand and it's only over the last 2-3 years that a picture is beginning to emerge of what viruses are endemic to this country and what disease syndromes they are involved with. There's still much to be learnt in this field; however, with active virology groups now working at the Ruakura and Wallaceville Animal Health Laboratories and at Massey University, many of the gaps in our knowledge should be filled over the next few years. HORSES VIRUSES
Equine herpesviruses There are three types of equine herpesvirus - equine herpesvirus type I (EHV I) is probably the most common cause of respiratory disease in horses under 2 years of age throughout the world; the older name is equine rhinopneumonitis virus. In young foals a fatal pneumonia can occur. Occasionally abortion or central nervous disease resulting in paralysis can follow infection of mares with EHVI. Recent overseas work suggests that more virulent strains of the virus are involved in the abortion outbreaks, and this may explain why in a number of countries in the world (England, Australia, New Zealand) respiratory disease due to EHVI is common whereas abortion due to the virus is rare. Both strains of EHV 1 have been isolated recently in New Zealand; that is the respiratory and the abortion strains. The respiratory isolates were made during an outbreak ofrespiratory disease initially involving 10 foals and 4 yearlings. The foals affected were between 2 and 4 months of age - at about the age their colostral immunity could be expected to be waning. A further outbreak of respiratory disease occurred 12 months later at the same stud (where the original isolates had been made) and in the next crop offoals, suggesting that the resident mares were harbouring the virus latently. To digress a little, the herpesvirus grou p generally are renowned for causing latent infections (take the cold sore situation in man) and clinical disease with shedding of the virus may re-occur after some stressful situation has been present. To my knowledge there has only been one confirmed outbreak of abortion due to EHVI in New Zealand. Six mares aborted on the affected stud; the abortions occurred during late
* t
Ruakura Animal Research Station. Private Bag. Hamilton. Presented to the NZVA Annual Conference 1977.
pregnancy (8Yz months to full term). Whenever multiple abortions occur at a stud it would be well worthwhile taking specimens to check that EHV I is not involved. Take a full range of specimens as the histopathology or the condition is quite characteristic. The central nervous form of the disease has never been reported in New Zealand; however, a case of non-suppurative encephalitis was seen recently in a Canterbury horse which may have been attributable to this virus, so we should keep this condition in mind when confronted by horses with ataxia and paralysis. The second group of equine herpesviruses are the slowly growing, cell associated, type 2 equine herpesviruses (EHV2). These are sometimes called the equine cytomegalo-viruses althoug~. in fact they do not cause cytomegaly in tissue culture. Many strains varying in virulence exist within this group, and there is still some controversy over whether this group of viruses causes clinical disease. EHV2 infections tend to be long-lasting, and evidence of antigenic drift within the group has been obtained. Most horses are affected during their lifetime. In some cases a mild respiratory disease has been associated with EHV2 viruses, and I feel certain at least some of the serotypes can be pathogenic. Often we isolate EHV2 viruses from horses with concurrent bacterial infections such as Group C streptocci and Strep. equi, and conseq uently a synergistic effect may well occur. The third equine herpesvirus is the coital exanthema virus. Although this virus has not yet been isolated in New Zealand there is plenty of clinical evidence of its presence, and I'm sure it's only a matter of time before it is isO'lated. EHV3 is venereally transmitted and causes pustular lesions on the vaginal and vestibular mucosa, and on the skin of the penis and prepuce of the stallion. It does not cause abortion. PIG VIRUSES
Aujesky's disease Aujesky's disease virus, or pig herpesvirus, was isolated for the first time in New Zealand in 1976. The disease is also known as pseudorabies or mad itch. This herpesvirus naturally affects pigs and rats, the main clinical manifestations being central nervous disease in young pigs, and reproductive failure in sows. Wallaceville Animal Health Reference Laboratory has been carrying out a large scale serological survey in an attempt to ascertain the incidence of the disease in this country. To date about 5700 sera have been tested and 16 properties have been found to have serological evidence of the disease. Most of the affected properties appear to be located in the southern half of the North Island, and, so far, the
Continued next page
336
NEW ZEALAND VETERINARY JOURNAL
disease doesn't seem to be widely distributed. It is important to remember that this virus can cause fatal infections in cattle sheep, cats and dogs which are all dead-end hosts. The usual signs are those of a severe pruritis progressing to paralysis and death, and usually close contact with pigs or wild rats is necessary before transmission will occur. Encephalomyocarditis (EMC) virus A number of isolations of this virus were recently made from an outbreak ofEMC in Northland, during which 40 pigs died. The c~usative virus is a rodent entero-virus which may infect young pigs (up to 4 months of age) causing a fatal non-suppurative myocarditis. The affected pigs die suddenly, often without sho,:ing any preliminary clinical signs, and the necropsy findlllgs suggest acute heart failure. There are usually pericardial effusions, hydrothorax and ascites, with small white or yellowish flecks being present in the myocardium. . The main disease to differentiate from EMC is mulberry heart disease, which is acondition associated with vitamin E/selenium deficiency. . EMC occurs mainly on poorly managed piggeries where opportunities exist for pigs to ingest dead rodents or eat food contaminated by rodent faeces. In Australia, outbreaks of the disease have been associated with the rodent plagues that occur occasionally in that country. Pig parvovirus A number of isolations of this virus have been· made from aborted or mummified piglets over the last 2 years. This virus has the capacity to cause reproductive failure, especially in gilts. The syndrome seen is one of gilts producing a mixture of stillborn, mummified and live piglets. The serological evidence indicates that the virus is widespread throughout New Zealand, and the majority of pigs on an infected property will have antibody a?alllst .the . ViruS. Pig parvovirus doesn't cause any clinical disease III pigs after birth and indeed its pathogenic effects on foet~ses only occur if the virus reaches the foetus during a relatively short period during gestation (gestation days 30-60). For the virus to reach the foetus the sow must have no specific im~unoglobulin against PPY and, consequently, gilts are most at fisk as colostral immunity has waned by 21 weeks of age (range 14-36 weeks), and this means between 2% and 47% of all gilts may be susceptible to infection at the time of first service. Most older sows will have experienced a natural infection and consequently are immune to the abortigenic effects of the virus. BOVINE VIRUSES
Bovine rota virus and coronavirus The presence of both these viruses in New Zealand has been confirmed over the last few years. In both cases the viruses are difficult to adapt to grow in tissue culture and they are routinely screened by examining concentrated faecal preparations under the electron microscope. Both viruses have been implicated as a cause of calf diarrhoea. Many of the cases of "white scours", blamed in the past almost entirely on Escherichia coli, were probably caused by one of these two viruses. Generally only calves less than 4 weeks of age are susceptible, although the corona virus causes more severe lesions and may cause disease in older animals. The primary lesion seen with both viruses is epithelial cell damage, followed by replacement with immature cells and dwarfing of vii Ii, and the lesions are remarkably similar to those seen with transmissible gastoenteritis (TG E) in pigs. The epithelial loss results in malabsorption with diarrhoea and death resulting from the loss of ions, bicarbonate and serum protein which. in tum. leads. to acidosis and dehydration. Much of this effect is due to the hyperosmotic effect of undigested lactose. In regard to treatment; starvation, water and ion replacement and bicarbonate treatment are usually more effective than antibiotic therapy.
VOL. 25
Absorbed colostral antibody circulating in the blood is not protective and it appears that adequate levels of specific viral antibody must be present in the gut lumen at the time of challenge to protect the calves. Often herds suffer outbreaks of diarrhoea every year and these recurrent out b rea ks may be due to repeated infections and the excretion of virus by immune animals, as there appears to be litt~e age-resistance. Also the rotavirus in particular is highly resistant and will survive in contaminated buildings for some months. Concurrent infections with other bacteria (E. coli, Providencia stuartii) and other viruses (parvovirus, adenovirus, enterovirus) may well raise the pathogenicity of these calf diarrh oea viruses. Parainfluenza 3 virus ~I3 virus was isolated from cattle for the first time in this country III 1975. Although there was serological evidence to show it was widespread in New Zealand cattle (almost 90% of cattle had antibodies against PI3 virus in one survey), no isolations of the virus had previously been made from cattle with disease. The first isolates were made during an outbreak of upper respiratory disease involving 12 of 220 yearling beef cattle. The disease. was clinically mild and the symptoms seen were pyrexia, anoreXia, some loss of condition, serous ocular and nasal discharges and harsh tracheal rales. The protracted recovery shown bysome of the bulls and the apparent development of an allergic rhllllhs was of some interest as the role of viruses in the production of chronic granular rhinitis is yet unknown. It is probable that most PI3 infections are usually subclinical, a~though with the advent of indoor calf rearing schemes this ViruS, together with other viruses such as adenoviruses, respiratory syncytial virus, rhinoviruses and reoviruses, may 'well a~sume a more significant role as a cause of bovine respiratory disease.
,
DOG VIRUSES
Canine herpesvirus This virus was isolated for the first time in New Zealand several months ago from a case of "fading puppy" syndrome. It is the cause of a fatal systemic infection of puppies during the first 3 weeks of life. Older dogs may also become infected; however, although they can develop a mild upper respiratory or genital disease, infections are usually symptomless. The puppies can be infected in utero, or by exposure to the virus in the vagina during parturition, or by inhalation after birth. Abortion can follow in utero infection. It is believed the generalised disease in newborn puppies is due to their inability to regulate and maintain their body temperature. Certainly optimal growth of the virus in tissue culture occurs at 35-36°C. CAT VIRUSES
Feline herpesvirus and caliciviruses A number of isolations of these viruses have been made at various laboratories over the last few years. Both viruses cause upper respiratory disease, with the lungs being spared unless very young kittens are involved, or unless secondary bacterial infection becomes superimposed on the original infection. The feline herpesvirus (also known as feline viral rhinotracheitis) is the more severe pathogen of the two. causing conjunctivitis, sneezing, buccal ulceration and drooling of saliva. As with other herpesviruses, abortion may occur in pregnant queens. The feline caliciviruses are a group of agents which have an affinity for the respiratory tract mucosa. and resemble in many ways the rhinoviruses of man - the cause of the common cold. There are a large number of serotypes which vary'greatly in virulence. The occasional more virulent strain of calicivirus can cause a severe respiratory disease with pneumonitis, tongue ulceration and a mortality rate of up to 30% in kittens.
335
NEW ZEALAND VETERINARY JOURNAL
Some recent virus isolations and their importance in New Zealandt G.
w. Horner*
N.Z. \·er.J.25:335-36
INTRODUCTION
Today I am going to talk about some of the animal viruses which have been isolated recently in New Zealand and, along the way, I will make a few comments on the possible clinical significance of these various viruses. Veterinary virology is still in its infancy in New Zealand and it's only over the last 2-3 years that a picture is beginning to emerge of what viruses are endemic to this country and what disease syndromes they are involved with. There's still much to be learnt in this field; however, with active virology groups now working at the Ruakura and Wallaceville Animal Health Laboratories and at Massey University, many of the gaps in our knowledge should be filled over the next few years. HORSES VIRUSES
Equine herpesviruses There are three types of equine herpesvirus - equine herpesvirus type I (EHV I) is probably the most common cause of respiratory disease in horses under 2 years of age throughout the world; the older name is equine rhinopneumonitis virus. In young foals a fatal pneumonia can occur. Occasionally abortion or central nervous disease resulting in paralysis can follow infection of mares with EHVI. Recent overseas work suggests that more virulent strains of the virus are involved in the abortion outbreaks, and this may explain why in a number of countries in the world (England, Australia, New Zealand) respiratory disease due to EHVI is common whereas abortion due to the virus is rare. Both strains of EHV 1 have been isolated recently in New Zealand; that is the respiratory and the abortion strains. The respiratory isolates were made during an outbreak ofrespiratory disease initially involving 10 foals and 4 yearlings. The foals affected were between 2 and 4 months of age - at about the age their colostral immunity could be expected to be waning. A further outbreak of respiratory disease occurred 12 months later at the same stud (where the original isolates had been made) and in the next crop offoals, suggesting that the resident mares were harbouring the virus latently. To digress a little, the herpesvirus grou p generally are renowned for causing latent infections (take the cold sore situation in man) and clinical disease with shedding of the virus may re-occur after some stressful situation has been present. To my knowledge there has only been one confirmed outbreak of abortion due to EHVI in New Zealand. Six mares aborted on the affected stud; the abortions occurred during late
* t
Ruakura Animal Research Station. Private Bag. Hamilton. Presented to the NZVA Annual Conference 1977.
pregnancy (8Yz months to full term). Whenever multiple abortions occur at a stud it would be well worthwhile taking specimens to check that EHV I is not involved. Take a full range of specimens as the histopathology or the condition is quite characteristic. The central nervous form of the disease has never been reported in New Zealand; however, a case of non-suppurative encephalitis was seen recently in a Canterbury horse which may have been attributable to this virus, so we should keep this condition in mind when confronted by horses with ataxia and paralysis. The second group of equine herpesviruses are the slowly growing, cell associated, type 2 equine herpesviruses (EHV2). These are sometimes called the equine cytomegalo-viruses althoug~. in fact they do not cause cytomegaly in tissue culture. Many strains varying in virulence exist within this group, and there is still some controversy over whether this group of viruses causes clinical disease. EHV2 infections tend to be long-lasting, and evidence of antigenic drift within the group has been obtained. Most horses are affected during their lifetime. In some cases a mild respiratory disease has been associated with EHV2 viruses, and I feel certain at least some of the serotypes can be pathogenic. Often we isolate EHV2 viruses from horses with concurrent bacterial infections such as Group C streptocci and Strep. equi, and conseq uently a synergistic effect may well occur. The third equine herpesvirus is the coital exanthema virus. Although this virus has not yet been isolated in New Zealand there is plenty of clinical evidence of its presence, and I'm sure it's only a matter of time before it is isO'lated. EHV3 is venereally transmitted and causes pustular lesions on the vaginal and vestibular mucosa, and on the skin of the penis and prepuce of the stallion. It does not cause abortion. PIG VIRUSES
Aujesky's disease Aujesky's disease virus, or pig herpesvirus, was isolated for the first time in New Zealand in 1976. The disease is also known as pseudorabies or mad itch. This herpesvirus naturally affects pigs and rats, the main clinical manifestations being central nervous disease in young pigs, and reproductive failure in sows. Wallaceville Animal Health Reference Laboratory has been carrying out a large scale serological survey in an attempt to ascertain the incidence of the disease in this country. To date about 5700 sera have been tested and 16 properties have been found to have serological evidence of the disease. Most of the affected properties appear to be located in the southern half of the North Island, and, so far, the
Continued next page
336
NEW ZEALAND VETERINARY JOURNAL
disease doesn't seem to be widely distributed. It is important to remember that this virus can cause fatal infections in cattle sheep, cats and dogs which are all dead-end hosts. The usual signs are those of a severe pruritis progressing to paralysis and death, and usually close contact with pigs or wild rats is necessary before transmission will occur. Encephalomyocarditis (EMC) virus A number of isolations of this virus were recently made from an outbreak ofEMC in Northland, during which 40 pigs died. The c~usative virus is a rodent entero-virus which may infect young pigs (up to 4 months of age) causing a fatal non-suppurative myocarditis. The affected pigs die suddenly, often without sho,:ing any preliminary clinical signs, and the necropsy findlllgs suggest acute heart failure. There are usually pericardial effusions, hydrothorax and ascites, with small white or yellowish flecks being present in the myocardium. . The main disease to differentiate from EMC is mulberry heart disease, which is acondition associated with vitamin E/selenium deficiency. . EMC occurs mainly on poorly managed piggeries where opportunities exist for pigs to ingest dead rodents or eat food contaminated by rodent faeces. In Australia, outbreaks of the disease have been associated with the rodent plagues that occur occasionally in that country. Pig parvovirus A number of isolations of this virus have been· made from aborted or mummified piglets over the last 2 years. This virus has the capacity to cause reproductive failure, especially in gilts. The syndrome seen is one of gilts producing a mixture of stillborn, mummified and live piglets. The serological evidence indicates that the virus is widespread throughout New Zealand, and the majority of pigs on an infected property will have antibody a?alllst .the . ViruS. Pig parvovirus doesn't cause any clinical disease III pigs after birth and indeed its pathogenic effects on foet~ses only occur if the virus reaches the foetus during a relatively short period during gestation (gestation days 30-60). For the virus to reach the foetus the sow must have no specific im~unoglobulin against PPY and, consequently, gilts are most at fisk as colostral immunity has waned by 21 weeks of age (range 14-36 weeks), and this means between 2% and 47% of all gilts may be susceptible to infection at the time of first service. Most older sows will have experienced a natural infection and consequently are immune to the abortigenic effects of the virus. BOVINE VIRUSES
Bovine rota virus and coronavirus The presence of both these viruses in New Zealand has been confirmed over the last few years. In both cases the viruses are difficult to adapt to grow in tissue culture and they are routinely screened by examining concentrated faecal preparations under the electron microscope. Both viruses have been implicated as a cause of calf diarrhoea. Many of the cases of "white scours", blamed in the past almost entirely on Escherichia coli, were probably caused by one of these two viruses. Generally only calves less than 4 weeks of age are susceptible, although the corona virus causes more severe lesions and may cause disease in older animals. The primary lesion seen with both viruses is epithelial cell damage, followed by replacement with immature cells and dwarfing of vii Ii, and the lesions are remarkably similar to those seen with transmissible gastoenteritis (TG E) in pigs. The epithelial loss results in malabsorption with diarrhoea and death resulting from the loss of ions, bicarbonate and serum protein which. in tum. leads. to acidosis and dehydration. Much of this effect is due to the hyperosmotic effect of undigested lactose. In regard to treatment; starvation, water and ion replacement and bicarbonate treatment are usually more effective than antibiotic therapy.
VOL. 25
Absorbed colostral antibody circulating in the blood is not protective and it appears that adequate levels of specific viral antibody must be present in the gut lumen at the time of challenge to protect the calves. Often herds suffer outbreaks of diarrhoea every year and these recurrent out b rea ks may be due to repeated infections and the excretion of virus by immune animals, as there appears to be litt~e age-resistance. Also the rotavirus in particular is highly resistant and will survive in contaminated buildings for some months. Concurrent infections with other bacteria (E. coli, Providencia stuartii) and other viruses (parvovirus, adenovirus, enterovirus) may well raise the pathogenicity of these calf diarrh oea viruses. Parainfluenza 3 virus ~I3 virus was isolated from cattle for the first time in this country III 1975. Although there was serological evidence to show it was widespread in New Zealand cattle (almost 90% of cattle had antibodies against PI3 virus in one survey), no isolations of the virus had previously been made from cattle with disease. The first isolates were made during an outbreak of upper respiratory disease involving 12 of 220 yearling beef cattle. The disease. was clinically mild and the symptoms seen were pyrexia, anoreXia, some loss of condition, serous ocular and nasal discharges and harsh tracheal rales. The protracted recovery shown bysome of the bulls and the apparent development of an allergic rhllllhs was of some interest as the role of viruses in the production of chronic granular rhinitis is yet unknown. It is probable that most PI3 infections are usually subclinical, a~though with the advent of indoor calf rearing schemes this ViruS, together with other viruses such as adenoviruses, respiratory syncytial virus, rhinoviruses and reoviruses, may 'well a~sume a more significant role as a cause of bovine respiratory disease.
,
DOG VIRUSES
Canine herpesvirus This virus was isolated for the first time in New Zealand several months ago from a case of "fading puppy" syndrome. It is the cause of a fatal systemic infection of puppies during the first 3 weeks of life. Older dogs may also become infected; however, although they can develop a mild upper respiratory or genital disease, infections are usually symptomless. The puppies can be infected in utero, or by exposure to the virus in the vagina during parturition, or by inhalation after birth. Abortion can follow in utero infection. It is believed the generalised disease in newborn puppies is due to their inability to regulate and maintain their body temperature. Certainly optimal growth of the virus in tissue culture occurs at 35-36°C. CAT VIRUSES
Feline herpesvirus and caliciviruses A number of isolations of these viruses have been made at various laboratories over the last few years. Both viruses cause upper respiratory disease, with the lungs being spared unless very young kittens are involved, or unless secondary bacterial infection becomes superimposed on the original infection. The feline herpesvirus (also known as feline viral rhinotracheitis) is the more severe pathogen of the two. causing conjunctivitis, sneezing, buccal ulceration and drooling of saliva. As with other herpesviruses, abortion may occur in pregnant queens. The feline caliciviruses are a group of agents which have an affinity for the respiratory tract mucosa. and resemble in many ways the rhinoviruses of man - the cause of the common cold. There are a large number of serotypes which vary'greatly in virulence. The occasional more virulent strain of calicivirus can cause a severe respiratory disease with pneumonitis, tongue ulceration and a mortality rate of up to 30% in kittens.
