General information

Herpes viruses cause epidemic as well as latent or persistent diseases in almost all animal species. The name is derived from the Greek word “herpein” (to creep). Common to all herpesviruses is lifelong latency in the host organism.

Herpesviruses dog (CHV)

The so-called “puppy death” in dogs is caused by canine herpesvirus-1. Puppies under 3 weeks of age die of haemorrhagic systemic disease. There is massive lytic virus replication at a subnormal body temperature of 36 – 37 °C and death occurs within 48 hours. The morbidity rate is 100%, the mortality rate is almost 95%!

Older puppies usually show mild respiratory symptoms, that is why an aetiological involvement in kennel cough complex is attributed to CHV.

Adult animals usually go through clinically inapparent infections. CHV-1 leads to a latent infection; after a primary cell-lytic infection, the viruses retreat into the trigeminal and lumbosacral ganglion cells. In stressful situations (e. g. birth or incipient lactation), viruses may be reactivated and shed in oral, nasal and ocular secretions. Female dogs can transmit the virus in utero to the foetuses; abortions and stillbirths are rare. In adult immunocompromised animals, a peracute course of the disease with fatal outcome is possible. A diagnosis of breeding animals is recommended.

Herpesviruses cat (FHV)

The main symptoms of feline herpesvirus (FHV) are respiratory symptoms such as rhinitis and sinusitis with ocular and nasal discharge. Conjunctivitis develops and often corneal ulcers are formed. The cats suffer from dyspnoea and lack of appetite. These symptoms normally abate after a relatively short period of time. A latent infection develops which may be reactivated under stress at any time. This usually leads to recurrent rhinitis, which, however, is milder than in the primary infection. Complications are rare in FHV infections. Sometimes, the ocular changes are severe and the cat can go blind. Moreover, very young kittens with very high fever and general weakness may die (fading kitten syndrome).

Herpesviruses birds

There are many different herpesviruses that are found in birds, including commercial poultry, ornamental, wild and zoo birds. New viruses are also regularly found in these animal groups. Several herpesviruses have been described in parrots, too. The best-known and perhaps clinically most relevant one is psittacid herpesvirus 1 (PsHV-1).

PsHV-1 is responsible for Pacheco’s disease in parrots and is therefore also called Pacheco’s virus. The clinical course depends on the genotype or serotype and the affected psittacine species. For budgerigars and cockatiels, mild to subclinical courses with virus shedding are reported. In large parrots, such as macaws, amazon parrots, cockatoos or grey parrots, an infection often leads to death. If symptoms occur, they are usually unspecific and consist of anorexia, apathy and poorly developed feathers. Changes in faeces and an increase in uric acid excretion may occur, too. Occasionally, CNS symptoms are also observed. The disease particularly breaks out in stressful situations, e. g. capture and quarantine of imported birds, change of owner, hospitalisation, beginning of breeding or the onset of sexual maturity. Therefore, a suitable preliminary examination of birds that are to be integrated into the flock is recommended in order to avoid posing a threat to the other birds.

An examination for herpesviruses may also be appropriate for other animals with systemic diseases, diseases of the respiratory system, the liver or with skin lesions or lesions of the mucous membrane at the cloaca or around the beak.

In amazon parrots and cockatoos, psittacid herpesviruses can also be detected in papillomas in the throat and the cloaca.

Herpesviruses reptiles

Herpesvirus infections are most common in a variety of chelonians, including tortoises, terrapins and sea turtles. In the veterinary practice, herpesviruses of tortoises of the genus Testudo play an important role. As this is a highly contagious virus infection, animals should be routinely examined for infection before being introduced into a population.

Clinical symptoms include nasal and ocular discharge, regurgitation, anorexia and lethargy. Necrotic plaques in the oral cavity and on the tongue are also typical.

So far, 4 different types of herpesvirus, testudinid herpesvirus 1 – 4 (TeHV 1 – 4 ), are known in tortoises. In Europe, especially TeHV 1 and 3 are found. TeHV 3 has a broad host range among tortoises and infections are usually associated with very high morbidity and mortality rates. TeHV 1 can mostly be detected in Russian tortoises (Testudo horsfieldii). These are often diseases of individual animals, since TeHV 1 has a considerably lower tendency than TeHV 3 to spread in the population. Individual cases of TeHV 2 (especially in desert tortoises) and TeHV 4 (in African tortoises) have been detected in Europe in recent years.

In turtles, herpesvirus infections are mainly associated with hepatic inflammation. In live animals, dry throat swabs, and in dead animals, liver samples can be examined by PCR.

Herpesviruses cause fibropapillomatosis in sea turtles. Virus detection by PCR is possible from altered tissue.

In lizards, herpesviruses are mainly seen in connection with oral lesions.

Herpesviruses horse (EHV)

EHV 1 and 4

In horses, donkeys, mules and zebras, infections with EHV 1 as well as with EHV 4 are caused by droplet infection or direct contact. The severity of the clinical symptoms depends on the age and immune status of the infected animal. Particularly infections with EHV 1 are able to spread beyond the respiratory mucosa and cause severe manifestations of the disease: abortions, perinatal foal death, neurological diseases.

In case of foals infected with EHV 4, morbidity rates of up to 100% are possible, especially during the weaning period. More than 80% of the isolates come from animals with rhinopneumonitis. EHV 3, which does not cross-react with EHV 1 or 4, causes genital infections in horses.

Once horses are infected with herpesviruses, they remain carriers of the virus throughout their lives, and the virus can be reactivated endogenously under unfavourable conditions (stress, etc.). Lymph organs and the leukocyte fraction are the main latency organs. If the vaccinated horses are also taken into account, seroprevalence in the horse population is high.

In recent years, EHV-1-associated neurological diseases, for which a “neurotropic” strain of EHV 1 is held responsible, have been reported with increasing frequency and severity of the clinical disease. This much-feared clinical picture is referred to as EHM (equine herpesvirus myeloencephalopathy).

 

EHV 2 and 5

The involvement of EHV 2 and/or EHV 5 in keratoconjunctivitis has long been suspected and these viruses are indeed regularly detected in conjunctival swabs. In recent years, it has increasingly been shown that EHV 2 and 5 are precursors of other viral and bacterial infections of the respiratory tract. Especially in young animals, EHV 2 and/or 5 were detected in treatment-resistant, partly catarrhal-purulent, partly necrotising or abscessing bronchopneumonia. EHV 5 was recently presented as aetiological agent of “equine multinodular pulmonary fibrosis” (EMPF).

 

EHV 3

Coital exanthema caused by equine herpesvirus type 3 (EHV 3), which only sporadically occurs in Germany, is a mildly progressing breeding infection in horses. Clinically, blisters, pustules and erosions appear on the mucous membrane of the vestibulum, penis or prepuce as well as on adjacent skin areas. Healing takes place spontaneously after approximately 2 – 3 weeks, but can be complicated by secondary infections. Transmission mainly occurs through mating, but is also possible through close contact as well as rectal and vaginal examinations. Infected animals remain carriers of the virus for life.

Herpesviruses cattle (BHV)

Bovine herpesvirus 1 (BHV 1) is the causative agent of infectious bovine rhinotracheitis (IBR), also known as infectious pustular vulvovaginitis (IPV) and infectious balanoposthitis (IBP).

In Germany, it is an epizootic disease that is notifiable upon suspicion!

 

Herpesviruses koi (KHV)

Koi herpesvirus is a highly infectious virus that has caused epidemic disease in carps (koi and common carps) in recent years, depending on the water temperature. Morbidity and mortality rates can be as high as 100% within 1 – 2 weeks after the pathogen has been introduced. The incubation period ranges from a few weeks to several months. It depends on various external and internal factors such as stress and condition of the fish. Fish of all age groups are affected at water temperatures between 18 – 29 °C. Clinically, the main symptoms are gill necrosis, increased mucus production, haemorrhages of the skin, liver, spleen and kidneys. Surviving fish probably remain latent carriers of the virus for years and represent a potential hazard in the trade with live fish in pond management and hobby animal keeping. Immunisation by means of live attenuated vaccine is currently rejected from a scientific point of view.

In Germany, it is an epizootic disease that is notifiable upon suspicion!