Bovine Viral Diarrhea (BVD)

B) BVD

A veterinarian is called because of an aborted calf. What viral infection may cause abortion by directly infecting the foetus? A) FMD B) BVD C) Coronavirus D) Adenovirus

chronic MD

Although mortality usually approaches 100%, a few animals may survive the acute MD but are prone to develop the

B : BVD introduced by at least 1 persistently infected (PI) immunotolerant animal to a BVD free herd NOTE: Shipping fever does not present in this manner. Animals that travel usually present symptoms due to the stress and confinement, this are solely affecting the lower respiratory track (causing pneumonia). Foot and Mouth disease is an exotic disease to the US and in case of being introduced animals would be symptomatic, lesions would be localized in the oral mucosa, coronary bands, udders and scrotum.

An addition of 10 heifers to a herd of 100 has resulted in severe disease for 30 animals with signs of fever, nasal discharge, cough, many had diarrhea and some presented ulcerations in the mouth and muzzles. One of them died and erosions along the GIT were observed at necropsy. What is the most probable explanation? A : Shipping fever after a long transport of animals introduced into a naive herd B : BVD introduced by at least 1 persistently infected (PI) immunotolerant animal to a BVD free herd C : Foot and Mouth disease introduced by asymptomatic animals

B : Antigen ELISA NOTE: RT-PCR is also an alternative

An addition of 10 heifers to a herd of 100 has resulted in severe disease for 30 animals with signs of fever, nasal discharge, cough, many had diarrhea and some presented ulcerations in the mouth and muzzles. One of them died and erosions along the GIT were observed at necropsy. What test should be employed to identify the animal/s that introduced the disease into the herd? A : Antibody ELISA B : Antigen ELISA C : PCR D : Electron microscopy

- high - significantly high NOTE: mortality is seen via abortion and mucosal disease

BVD has a worldwide distribution and is highly important in dairy and beef cattle with _____ morbidity and __________ mortality

1) Superinfection with a homologous BVDV 2) Mutation of the ncp to cytopathic (cp) 73 variant* 3) Vaccination with attenuated BVDV strain homologous to the ncp PI virus. These calves can develop one of the two forms of mucosal disease: a) Acute MD b) Chronic MD *Cytopathic arising the novo by mutation (recombination, insertions, duplications, deletions and rearrangements)

Calves suffering from persistent infection (PI) and mucosal disease may appear clinically normal, but upon what situations this may change:

dehydrated and usually die within 3-10 dd

Cattle with acute MD become progressively

GI tract

Cytopathic BVD replicates in what region of the body?

1) Presumptive Dx is made based on clinical hx, reproduction records (low calving rates, increased calving intervals, high number of abortions), CS (in adult animals and in newborns), gross and microscopic lesions 2) For the MD form of BVD it is important to note that only a few animals will present clinically at a specific point in time as it only occurs in PI animals which should be a small proportion of the herd. 3) Samples include feces, nasal discharge, blood and tissues collected at necropsy and aborted fetuses 4) Viral Ag detection in feces (ELISA) or tissues (IHC) 5) RT-PCR 6) Paired samples to be tested by neutralization BUT interpretation of seronegative result must be made considering immunological tolerant state of some animals. 7) PI animals do not seroconvert and may be temporarily healthy therefore they are difficult to identify!!!! But they are shedding! • Virus isolation in cell culture, followed by IF

How is BVD diagnosed?

Cytopathic (cpBVDV)

In BVD disease, which biotype is NOT distributed widely throughout the host?

Noncytopathic (noncpBVDV)

In BVD disease, which biotype is distributed widely throughout the host?

Dramatic losses as a big outbreak will occur

In a virus free herd, the introduction of a PI animal will result in what?

Seminal vesicles and the prostate gland (causing venereal transmission). NOTE: When buying semen for artificial insemination (AI) a reliable source (ex. CSS, certified semen services) is recommended.

In persistently infected males BVDV replicates within where?

Detection and elimination of PI animals. NOTE: Avoid reintroduction of the virus by implementation of testing and quarantine of new animals. Antigen detection (ELISA) is frequently used specially in newborn calves in a herd with BVD circulating but can also use RT-PCR. Serology can be used to conduct surveillance to see if the virus is circulating in the herd but should NOT be used to test animals to be incorporated to a herd. Only allow mature immune animals into the herd.

Most important for control of BVD is what?

True NOTE: Infection with these viruses can also occur in sheep, goats, swine, deer and bison.

T/F: BVD has worldwide distribution and is highly important in dairy and beef cattle with high morbidity and significant mortality (abortions and mucosal disease).

True

T/F: The most efficient transmission is from PI individuals and not so much from acutely infected ones In herds where the virus is present, only sporadic losses occur when naïve animals are introduced as the rest have immunity

True

T/F: There are both low and high virulence strains in both biotypes. The primary replication occurs in tonsils and the nasal mucosa with virus spreading to lymph nodes, spleen and thymus but in the high virulence strain there can also be spread to T cell dependent areas and to the bone marrow and will eventually spread to all organs

True

T/F: These viruses are easily transmitted between animals and herds indirectly by fomites and contaminated food with feces, urine, oral or nasal secretion and amniotic fluid or semen from infected animals

1) Leukocytes 2) Lymphoid tissue 3) Proximal colon 4) Respiratory tract

The noncpBVDV replicates where?

GIT

The noncpBVDV replicates where?

Noncytopathic (noncpBVDV) NOTE: The high levels of viremia facilitate transplacental and intrauterine infections and cause abortions and persistently infected (PI) calves.

There is persistent viremia with which biotype due to its ability to inhibit Type I interferons?

1) Postnatal infection of non pregnant cattle 2) Infection of pregnant cows 3) PI in calves and MD

What are the CS of BVD?

1) Cytopathic (cpBVDV) 2) Noncytopathic (noncpBVDV) NOTE: BVDV can infect a wide variety of cells.

What are the biotypes of BVD?

1) BVD (acute) 2) Mucosal disease (this presentation only in persistently infected (PI) animals) NOTE: These are different disease syndromes caused by the same etiologic agent.

What are the different disease syndromes in cattle caused by the same etiological agent, Flavivirus?

1) Biphasic fever 2) Anorexia 3) Tachycardia 4) Polypnea 5) Decreased milk production 6) Watery diarrhea 7) Feces may contain blood and have foul odor 8) Erosions and ulcers may be present on the tongue, palate, and gingival while epithelial erosions may be pronounced in the interdigital regions, coronary bands, teats, vulva, and prepuce 9) Nasal-ocular d/c 10) Corneal opacity 11) Hypersalivation 12) Decreased rumination 13) Bloat

What are the symptoms of acute mucosal disease?

1) Intermittent diarrhea 2) Chronic bloat 3) Decreased appetite 4) Wt loss 5) Nasal-ocular d/c (commonly seen) NOTE: Cattle with chronic MD rarely survive past 18 months and are usually euthanized or die of severe debilitation

What are the symptoms of chronic mucosal disease in affected cattle?

BVD

What is seen here?

Epithelial necrosis and massive destruction of lymphoid tissues (especially Peyer's patches)

What is seen histologically due to BVD?

Calves infected in utero between 80 - 125 dd may be PI are therefore immunotolerant to noncytopathic (ncp) BVDV.

What is seen with calves infected with persistent infection (PI) in calves and mucosal disease (MD)?

1) Cattle of all ages are susceptible. 2) Younger animals (after maternal antibodies decline) are more commonly affected. The incubation is 5-7 days when fever and panleukopenia appear but otherwise in most animals the infection is trivial. 3) In some cattle, diarrhea may appear, some may have nasal and ocular discharge and present erosive stomatitis. In dairy cows there is a drop in milk yield. Because of the immunosuppression (panleukopenia), it is not uncommon to see secondary respiratory and GI bacterial infections.

What is seen with postnatal infection of non-pregnant cattle?

1) Transplacental spread occurs frequently. 2) The outcome depends on the virus strain and the age of the fetus (immunologic maturity). 3) Early infections result in resorption (<80 dd of pregnancy). Bovine fetal immunologic competence is reached at 125 dd of pregnancy. If infection occurs between days 80-125, calves may become immunotolerant to BVDV and thus they will be PERSISTENTLY INFECTED (PI). That is because the immune system is starting to recognize Ag but have not reached the point were it differentiates between self and nonself antigens, thus the viruses' antigens are not recognized as foreign resulting in no response to them. After day 125, viral antigens are viewed as foreign and faught, with possible outcomes being: abortions, weak calf syndrome or congenital defects (mostly of the central nervous system (CNS) such as brain and spine, and also the retina). 4) The most common defect is cerebellar hypoplasia which manifests as ataxia, tremors, wide stance, stumbling and/or death

What is seen with postnatal infection of pregnant cattle?

At 6-10 mos. Inactivated vaccines have only limited success (used in pregnant animals), attenuated vaccines are mostly used but they can cause PI animals to develop mucosal disease and cause abortions, stillbirths and birth defects.

When is vaccination for BVD done?

Cytopathic (cpBVDV)

Which BVD biotype induces a cell mediated immune response?

Noncytopathic (noncpBVDV)

Which BVD biotype induces humoral immune response?