What is Herpesvirus Infection?
The herpesvirus family can induce persistent infections that can last or intermittently reoccur over many weeks, months, and even years. All infected birds will carry the virus throughout their lifetimes, and can shed the disease at any time, spreading it to other birds. While treatment and vaccines for some strains are available, they are not always successful, and often come too late in the progression of the disease. Due to the inability to completely cure this disease, prevention remains the best strategy to ensure the health of your bird.
Herpesvirus is a widespread DNA virus that infects many types of birds, both wild and companion pets. Primarily, the various strains of herpesviruses affects lymphatic tissues, nerve cells, and epithelial cells, such as those in skin, mucosa, and the liver, but many other parts of the body can be affected as well. While difficult to identify in early stages, the herpesvirus often results in internal papillomas that affect various organs, and can be fatal.
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Symptoms of Herpesvirus Infection in Birds
Symptoms are quite varied between the many strains of herpesvirus that are spread from bird to bird during times of shedding. Another difficulty in noticing if your bird has been infected with the herpesvirus is that birds are often asymptomatic before signs suddenly appear that lead to death, or are silent carriers of the disease. Due to space, only the symptoms of some of the more common strains are listed.
Pacheco’s Disease, or Psittacine Herpesvirus
- Loss of appetite
- Regurgitation of clear mucus
- Green urine
- Bright yellow urine with little feces
- Blood in the droppings
- Papillomas in the oral cavity, eyes, or cloacal mucosa
- Abdominal distention due to an enlarged liver, spleen, or kidneys
- Sudden death
- Papilloma lesions on feet
- Discharge from eyes, nasal cavity or mouth
- Open beaked breathing
- Eye infections
- Decreased egg hatchability
- Bloody mucus
- Head shaking
- Difficulty breathing
- Swelling of sinuses
- Nasal discharge
- Watery eyes
- Paralysis of legs and wings
- Lymphoma growths on the skin around feather follicles
- Lymphomas in the skeletal muscles
There are three recognized subfamilies that help to classify the various strains of the herpesvirus, namely alpha, beta, and those that are not classified.
This family includes Infectious Laryngotracheitis, a common occurrence in chickens, Amazon tracheitis, which affects chickens and Amazon parrots, and the Duck plague.
This is a rather larger family, encompassing many of the herpesvirus strains seen in wild bird species, such as pigeons, falcons, owls, eagles, and cranes. Also included are the two most common strains seen in pet birds.
Also known as Psittacine herpesvirus, this disease causes internal papilloma growth in parrots, usually in the digestive tract. Common species affected are macaws, Amazon parrots, hawk-headed parrots, conures, and cockatoos. Of this type of herpesvirus, PsHV-1, there are four distinct genotypes, and infection of the Psittacine herpesvirus depends on the genotype, what species is exposed, and other relevant factors. In some species, this is a fatal infection, while others seem to be resistance to the disease.
This affects budgerigars and Double-yellow Headed Amazons.
This type of the herpesvirus includes strains that affect turkeys, canaries, and Gouldian finches, as well as Marek’s disease, which affects the poultry industry.
This virus causes lymphoma growth in chickens, turkeys and quails.
Causes of Herpesvirus Infection in Birds
The cause of herpesvirus in birds is through transmission of the virus from bird to bird. Birds who are infected can show signs or be asymptomatic, in which case they can become silent carriers. Birds that have had clinical signs of the infection, but have recovered, also carry the virus within them. All infected birds remain chronic carriers, and can intermittently shed the virus at any time throughout their lives, thereby spreading it to any other bird in the environment. The virus can be shed through:
- Direct contact
- Air contamination, such as inhalation of infected dust
- Contaminated food or water
- Nasal discharge
- Scales or flakes of skin that have been shed
- Feather debris
- Infected eggs
- Spread by Darkling beetles (Alphitobius diaperinus)
Factors that can increase the chances of infection and shedding the disease are:
- Introduction of new birds
- Presence of another disease
- Hormonal changes
Diagnosis of Herpesvirus Infection in Birds
Due to the variable symptoms involved with different strains of the herpesvirus, often your veterinarian will need to narrow down other possible causes until the herpesvirus can be identified. Your vet will likely perform a full physical exam, and ask you about any history of exposure of your bird to diseases or toxins, as well as information about diet. Be sure to tell your veterinarian about any recent travel, exposure to new birds, or changes in the diet.
Blood samples will be taken, and swabs of the oral cavity or cloacal area can also be taken. With these samples, various tests will be run which can identify the herpesvirus, and in some cases, can even identify the specific strain and genotype. The PCR, or polymerase chain reaction test, is most commonly employed for this. Other tests can include electron microscopy, immunofluorescence methods, and the agar gel immunodiffusion (AGID) test. The feces can sometimes be examined for traces of the disease as well.
Due to the absence of symptoms in many cases, sudden death can occur before the virus can be diagnosed. Various biopsies and tests can determine cause of death, and should stimulate testing of the rest of the population in the bird’s environment.
Treatment of Herpesvirus Infection in Birds
Treatment of the herpesvirus in birds is often too late for birds showing symptoms. A vaccine can be given, but it is generally more successful in reducing mortality rates in the surrounding population.
Antiviral drugs can be given, such as acyclovir added to the feed. Any papillomas or lesions can be cauterized or surgically removed, but they return in many cases. Supportive treatments are often given, such as antibiotics for secondary infections and pain relievers.
The most important step after a diagnosis is to prevent the spread of the disease. Proper handling and hygiene techniques need to be employed, and any other birds within the same environment should be tested.
Recovery of Herpesvirus Infection in Birds
The progression and recovery of the herpesvirus depend on many factors, such as the type of virus involved and the species of bird infected. Some species can succumb to death due to complications of internal growths. Other birds who recover from the signs of an infection can shed the disease, and are still at risk of having an outbreak of symptoms at a later date. All infected birds, whether they show symptoms or not, will remain carriers for the remainder of their lives, and can possibly infect other birds.
Preventing a herpervirus infection in your bird can be difficult, as it is impossible to identify carrier birds in many cases. Vaccinations are available for only some of the strains of this virus. However, you can reduce the risk of your bird contracting the virus. Strategies to accomplish this include:
- House infected birds separately from healthy ones
- Thoroughly disinfect the environment of infected birds, properly disposing of feces
- Perform screening tests for infections in your birds on a regular basis
- Limit contact with new birds that have not been tested
- Vaccinate your birds