1. Pathogenesis
2. Symptoms
3. Diagnosis
4. Prevention

---

Dutch situation IBR causes direct damage to cattle farms and leads to trade barriers for the export of cattle, semen and embryos. International developments led to a national IBR eradication plan at the end of the last century. The aim was to eradicate the IBR virus in the Netherlands. Control of IBR in the Netherlands began in 1995. Until 1998, this was done through a voluntary certification programme. IBR-free cattle farms could officially establish this status by obtaining an IBR-free certificate.

After two years of preparation, the collective compulsory control of IBR started on May 1^st, 1998. Farmers without an IBR-free certificate were required to vaccinate their cattle with an IBR marker vaccine every six months. In early 1999 it was discovered that some of the live vaccine used was contaminated with BVD virus. Registration of the live marker vaccine was suspended and the vaccination requirement was suspended.

In 2000, the Steering Committee for IBR Control in the Netherlands formulated an action plan for the collective resumption of IBR control. This plan consisted of two elements:

• A mandatory approach on farms that, after 2 years, had not achieved the target of 'less than 50 percent infected cattle over 2 years old'.
• Financial incentives to encourage certification.

This plan of action was extensively explained and put to a vote at LTO (=Farmers Organisation) meetings in the fall of 2000. Four meetings were organized by the Steering Committee for IBR Control for non-LTO members. The outcome of the LTO member consultation was that 61 percent of the LTO members present at the meeting voted in favour of the proposal. However, the required two-thirds majority set by LTO was not achieved, and thus the plan was rejected. The lack of visibility on compensation and the lack of trust in the IBR vaccine were identified as significant factors in the outcome. As a result, the collective control of IBR was suspended indefinitely, but continued on a voluntary level.

On June 9^th, 2017, the Secretary of the Ministry of Economic Affairs sent a letter to the House of Representatives announcing IBR regulations for all cattle owners in the first half of 2018. However this has not been implemented yet and is set for January 1^st, 2025.

In the meantime  April 1st, 2018, marked the beginning of a new phase of IBR eradication through mandatory vaccination of cattle on infected dairy farms since a requirement for participation in a program leading to an IBR-free dairy farm was implemented by the dairy organizations (ZuivelNL). Farms could choose between IBR-free (blood intake route, monitoring tank milk) with free status, IBR-free (tank milk route) with unsuspected status, or IBR-free (vaccination route) with 'vaccinated' status.

---

Pathogenesis

Bovine herpesvirus 1 (BoHV1) causes IBR (infectious bovine rhinotracheitis), IPV (infectious pustular vulvovaginitis) or IBP (infectious balanoposthitis), depending on the route of infection. BoHV1 belongs to the family Herpesviridae and the subfamily Alphaherpesvirinae. There are two subtypes of BoHV1: 1 and 2.

The virus is typically transmitted by direct contact between an infected cow and a susceptible cow. Transmission through humans and materials is also possible. In addition, the virus can be spread by air over short distances to other cattle.

Infected cattle can shed the virus for one to fourteen days. Symptoms of disease can appear two to seven days after infection. The circulation of IBR on a farm can last eight to ten weeks. Antibodies to glycoprotein E (gE) of BoHV1 take 3-4 weeks to appear, whereas antibodies to glycoprotein B (gB) appear faster.GD uses the gE-ELISA as the standard test for certification purposes (DIVA-concept).

After infection, the virus remains latent, mainly in the trigeminal or sacral ganglia, depending on the route of infection. Under the influence of stress or corticosteroids, the virus can reactivate, replicate and be shed. This process is usually subclinical, with less and shorter virus shedding than after primary infection. Infected cattle can potentially shed the virus throughout their lives. On IBR-positive farms, there may be no virus circulation for several years.

---

Symptoms

IBR infection leads to inflammation of the upper respiratory tract. Viremia is usually undetectable. Infection is associated with immunosuppression. Symptoms of IBR infection may include nasal and ocular discharge, redness of the nose, lesions in the nose, fever, sniffling, sudden loss of appetite and production, lethargy, shortness of breath, sometimes accompanied by snoring. Mortality may occur. The unborn foetus is highly susceptible to IBR infection, leading to abortion (often in the second half of pregnancy). Pustular inflammation of the vulva or penis occurs in IPV and IBP. Multisystemic signs in young calves have also been described.

The classic symptoms of IBR (IPV/IBP) are not always present. Spread of the virus where cattle show no or very few symptoms is common. Virulence and clinical signs vary between different strains of the virus.

---

Diagnosis

The presumptive diagnosis is based on clinical signs. For rapid confirmation, nasal swabs from animals in the acute phase (fever, conjunctivitis, sniffing) can be taken for virological examination. Routine PCR testing is carried out in the laboratory.

Standard testing methods

• gE-ELISA: The gE ELISA in combination with the gE marker vaccine is the standard test for the detection of BoHV1 antibodies in tank milk, individual milk samples and blood. Cattle vaccinated with the gE marker vaccine, free of field virus, are considered IBR-free with a favourable test result. In about 90 per cent of favourable tank milk tests, the number of infected animals is less than ten per cent. The gE-ELISA does not detect antibodies quickly after infection; it can take 3 to 4 weeks.
  Note: Testing for BoHV1 antibodies within one week of vaccination with an inactivated marker vaccine can sometimes give a weak false positive result, even if the cattle have no antibodies to the field virus. It is therefore advisable to wait at least two weeks after vaccination before testing for antibodies.
• gB-ELISA: When it is necessary to demonstrate that cattle are free of antibodies to both the field and gE-negative marker vaccine virus, the gB-blocking ELISA is used. In this case, the serum is tested at a 1:10 dilution. The gB-ELISA detects antibodies rapidly, as early as 8 days after infection. The test is qualitative: results are reported as either antibodies detected or not detected, and occasionally as doubtful. For artificial insemination (AI) purposes, this test is used in its most sensitive form, with undiluted serum. This is sometimes required for export.
• Danish Test: AI organisations use the highly sensitive Danish test. This test does not discriminate between vaccinated and infected animals, i.e. it detects antibodies after vaccination with a gE-negative vaccine. This test is sometimes required for export.

Virological Tests

Virological diagnosis of IBR infection is based on real-time PCR and/or virus isolation. Nasal swabs are routinely tested by PCR for the presence of field or vaccine virus and this test can also be done at necropsy when macroscopic findings suggest IBR. Semen samples can be tested by both PCR and virus isolation.

• PCR: Real-time PCR is used for routine diagnosis of IBR infection. PCR combines high sensitivity with rapid results. The test distinguishes between field virus and vaccine virus. If the swabs are sent to GD before 9.00 a.m., you will usually receive the results in the afternoon or the next day.
• Virus Isolation: To determine the nature of the field virus, the virus must be isolated and further characterised. Virus isolation takes ten to fourteen days and is costly. Such research is only carried out as part of projects.

---

Prevention

The implementation of closed confinement reduces the risk of introducing IBR and other cattle diseases such as BVD, leptospirosis, paratuberculosis and salmonellosis. A farm takes the following measures to prevent the introduction of IBR:

• No purchase of cattle (except from IBR-free certified farms).
• No contact with cattle from non-certified farms (minimum distance of four metres from non-free cattle).
• All professional visitors must wear farm clothing and boots.
• Use clean equipment when in contact with cattle (including that of professional visitors).

There is still a risk of reactivation on non-IBR-free certified farms. This means that this strategy for IBR only provides sufficient safety when combined with removal of infected cattle and/or vaccination.