IV TH KEITH GOODERHAM WATERFOWL LECTURE Major viral diseases of waterfowl and their control

By Prof. Dr. Vilmos Palya developed one step or multiplex Director of Scientific Support reverse transcriptase-polymerase and Investigation Laboratory chain reaction (RT-PCR) methods Ceva-Phylaxia Veterinary are capable to detect and distinguish Biologicals Co., Budapest. between the different DHV types including the new variant DHV-1 lthough chickens and turkeys type as well. comprise the majority of Typing of duck hepatitis viruses is Apoultry species seen by the important to identify emerging veterinary practitioner, occasionally serotypes because immunisation is waterfowl such as ducks and geese serotype specific and does not con - are encountered. fer protection against infection with A feature that is unique to water - heterologous serotypes. fowl is that their environment usu - To prevent the disease, keep age ally involves the presence of groups isolated particularly during man-made or natural bodies of the first five weeks of life. Contact water, and this may enhance the co- with wild waterfowl should be mingling of free-living waterfowl avoided. Rats have been reported as species with the domestic flock and a reservoir of the virus, therefore ultimately, promote disease trans - pest control is important. mission. Vaccination of breeder ducks with Additionally, environmental condi - Fig. 1. Dead duckling in a typical ‘arched-backwards’ position from an attenuated live duck virus hepati - tions may also influence disease infection with DHV type 1. tis vaccine, using type 1 virus, pro - manifestation in domestic water - vides maternal immunity that fowl. There are many diseases that induce hepatitis in DHV type 1- lings over four weeks of age. The effectively prevents high losses in can affect waterfowl species. The immune ducklings, they are now onset of the disease is very rapid, it young ducklings. infectious diseases described here classified as member of the spreads quickly through the flock The vaccine is administered by the are the most common viral diseases Astroviridae family. and may cause up to 90% mortality. subcutaneous route in the neck to seen in domestic waterfowl species. Recently, in Taiwan and Korea Sick ducklings develop spasmodic breeder ducks at two or three times It seems likely that viral diseases will new serotypes of duck hepatitis contractions of their legs and die before the birds come into lay and assume greater future importance as virus, belonging to the same virus within an hour in a typical ‘arched- thereafter every 12 weeks during causes of disease in waterfowl. family as DHV-1 have been backward’ position (Fig. 1). The liver the laying period. At least three Greater attention needs to be described, which showed no anti - is enlarged and shows haemorrhagic immunisations are advisable for ade - given to the study of this source of genic relationship with DHV-1 in spots (Fig. 2). quate passive protection of duck - disease. cross-neutralisation test. Ducklings Diagnosis aiming to distinguish lings. Inactivated DHV-1 vaccine for are most susceptible to DHV at between infections caused by DHV- use in breeder ducks that have been younger ages and gradually become 1, DHV-2 and DHV-3 has been previously primed with live vaccine Duck virus hepatitis more resistance as they grow older. regarded difficult by gross and has also been described. The disease is rarely seen in duck - microscopic examination. Recently Modified live DHV-1 vaccine can Duck hepatitis (DH) is a highly fatal, also be used for early vaccination of contagious and rapidly spreading dis - Fig. 2. Enlarged liver with punctuate haemorrhages caused by DHV-1. progeny of non-immune breeders. ease of young ducklings, 1-28 days The vaccine is administered by the of age. So far, three different viruses, subcutaneous route or by foot web duck hepatitis virus (DHV) type 1, 2 stab in a single dose to day old duck - and 3, have been associated with lings. The birds rapidly develop an these disease conditions. active immunity within 3-4 days. DHV-1 has, since the first out - Hyperimmune serum to DHV-1, break in 1949 in Long Island, been prepared from the egg yolk of reported to infect ducklings world - hyperimmunised chickens, applied wide and is of most economic by SC in the neck, at the time of the importance to all duck growing onset of the disease, is an effective farms because of high potential mor - treatment of affected flock. tality when infection is not con - trolled. Molecular characterisation of the DHV-1 genome recently Duck virus enteritis showed that the genome organisa - tion classifies this virus as unassigned Duck virus enteritis (DVE) is an species in the family Picornaviridae. acute, sometimes chronic, conta - DHV type 2 and 3 are recognised as gious virus infection that occurs nat - separate entities because they Continued on page 23

International Poultry Production — Volume 19 Number 4 21 Continued from page 21 from 10-60%, and mortality from 2- urally only in ducks, geese and 20%. Mortality is always higher in swans, all members of the family young flocks (2-3 weeks of age) than Anatidae of the order Anseriformes. if infection occurs at a older age. In duck-producing areas of the The clinical signs in the acute world where the disease has been phase include a general malaise, reported, DEV has produced signifi - accompanied by diarrhoea of sick cant economic losses in domestic birds. and wild waterfowl due to mortality The affected birds are reluctant to and decreased egg production. The move when disturbed. Muscovy aetiological agent, a herpesvirus, is a ducks and goslings that survive the member of the alphaherpesvirinae acute phase of the disease are subfamily of the Herpesviridae fam - markedly stunted in growth and ily. especially geese develop lameness. This disease is most likely to affect The hock and metatarsal or digital mature ducks, but DVE has been joints, as well as the gastrocnemius reported in birds ranging from seven and digital flexor tendons, and days of age to mature breeders. In sometimes the synovial bursae are susceptible flocks the first signs are Fig. 3. Markedly swollen metatarsal joints. Reovirus infection of goose. markedly swollen (Fig. 3). often sudden, high and persistent By post mortem examination, reported to be as efficacious as during the acute phase of the dis - modified live vaccine. This vaccine ease, characteristic lesions can be has been tested only under labora - seen in the liver and spleen: in both tory conditions; it has not been organs multiple disseminated, grey - tested on a large scale and is not ish-white pin-head necrotic foci are licensed. present and they are larger than normal (Fig. 4). Sero-fibrinous epi- and pericardi - Reovirus infection tis, arthritis and tenosynovitis are frequently seen during the acute and Although avian orthoreoviruses have chronic phase of the disease. As a been isolated from different patho - consequence of the rupture of the logical entities of poultry, their tendon and surrounding tissues, pathological role has been con - large haemorrhages in the region of firmed only in a limited number of gastrocnemius flexor tendon are diseases, such as arthritis-tenosyn - observed in the chronic phase of the ovitis of chickens and stunting runt - disease. ing syndrome. By histology, miliary foci of necrotic Fig. 4. Disseminated, greyish- Fig. 5. Granuloma-like foci with A disease of Muscovy ducks hepatocytes or granuloma-like foci white pin-head foci in an necrotic centres and proliferat - caused by reovirus was first with necrotic centres and proliferat - enlarged liver from a reovirus ing macrophages in the liver described in South Africa in 1950, ing macrophages can be found in the infected goose. from a reovirus infected goose. then in France in 1972, where the liver and the spleen (Fig. 5). virus was isolated. Reoviruses have Diagnosis of the disease can be mortality with a significant drop in A live attenuated virus vaccine can been repeatedly isolated from geese based on the characteristic liver and egg production. In chronically be used to control DVE in birds and detection of antibodies to spleen lesions during the acute infected partially immune flocks only over two weeks of age. Fattening or reoviruses has also been reported. phase and on the development of occasional deaths occur. Recovered breeding ducks may be vaccinated However diseases caused by a arthritis/tenosynovitis during the birds may be carriers and may shed subcutaneously or intramuscularly to reovirus in this species was reported subacute-chronic phase. Classical the virus in the faeces over a period produce an active immunity. The only in 2003. The earliest onset of detection methods of the causative of years. vaccine virus is not thought to the disease, both in duck and goose virus involves the isolation of the Clinical signs and gross pathology spread by contact from vaccinated flocks, is between 7 to 10 days of virus in reovirus antibody negative associated with a DVE outbreak to unvaccinated ducks, as the unvac - age and may persist in an affected duck/goose embryo or embryo vary with the species, age and sex of cinated birds remain susceptible to flock until 7-10 weeks of age. liver cell cultures and detection by the affected birds, and the virulence infection. The outbreaks last for 2-4 weeks electron microscopy, all which are of the virus. The range of signs in An inactivated vaccine has been or even longer. Morbidity ranges laborious and time consuming. affected birds includes eye watering Recently however a rapid, sensi - loss of appetite, ataxia, watery diar - Fig. 6. Sero-fibrinous perihepatitis and ascites in subacute form of tive and broad-spectrum RT-PCR rhoea and nasal discharge. Derzsy’s disease. has become available for the detec - In ducklings 2-7 weeks of age, tion and identification of avian losses may be lower than in older reoviruses from cell cultures and birds and the signs associated with clinical samples. It is very important DVE infection include dehydration, to confirm the identity of reovirus loss of weight and blood-stained isolates upon an outbreak since vents. The gross lesions are charac - despite the common properties terised by vascular damage, with tis - shared between duck/geese and sue haemorrhages and diphtheroid chicken reoviruses, the two viruses lesions of the mucosal surfaces of are antigenically different and their the digestive tract. Eruptive lesions core protein coding genes show of the mucous lining of the oesopha - only 21-25% homology at nucleotide gus and intestine are characteristic and amino acid levels. signs of DVE. Necrotic plaques may Although reovirus disease of be observed in the cloaca. Muscovy duck and goose continues Microscopic lesions are charac - to cause heavy losses to the terised by vascular damage and its Muscovy duck and goose industry, consequences in visceral organs. specific prevention of the disease Eosinophilic intranuclear inclusions has not been developed. Field and cytoplasmic inclusions in epithe - attempts to protect with an inacti - lial cells of the digestive tract are vated duck reovirus vaccine were typically present. Continued on page 24

International Poultry Production — Volume 19 Number 4 23 Fig. 7. Catarrhal/fibrinous/necrotic/haemorrhagic enteritis in acute Fig. 8. Growth retardation and loss of feathers in chronic form of form of Derzsy’s disease. Derzsy’s disease. Continued from page 23 economic losses up to 6-8 weeks of immunosuppressive viruses (reo- maternal antibodies, their levels and unsuccessful, despite the promising age. virus, circovirus) and mycoplasmas heterogeneity within a flock and the experimental results. A live vaccine Depending on the age when infec - tends to aggravate the clinical dis - susceptible period of goslings and prepared from non-pathogenic or tion occurs, the disease may be pre - ease by their synergic effect and ducklings to the disease. Breeder attenuated reovirus did not induce sent in either acute or subacute or prolongs the sensitivity period to the geese and Muscovy ducks that have immunity or protection. A subunit chronic forms in goose and Muscovy clinical manifestation of the disease been naturally infected or vaccinated vaccine consisting of baculovirus- duck, while SBDC of mule duck up to nine weeks of age. After this transfer maternal antibodies via the expressed major capsid protein was always takes the chronic form. susceptible period the birds can still egg yolk to their progeny. found non-immunogenic. During the acute phase of the dis - be infected which causes serological This passively acquired antibody ease, infected animals excrete huge response without clinical symptoms. may persist until 2-4 weeks of age quantity of virus into the environ - The disease may be complicated depending on the day-old antibody Parvovirus infection ment with their faeces which dis - with secondary bacterial pathogens: levels of individual birds. Since the seminates the infection rapidly in the E. coli, Streptococcus sp, disease is confined to young geese Waterfowl parvoviruses – goose flock. Pasteurellas, etc. and Muscovy ducks, control mea - parvovirus (GPV) and Muscovy duck Recovered animals or those Clinical diagnosis is not sufficient, sures have been aiming at providing parvovirus (MDPV) – cause the infected at a later age can become especially during the chronic phase adequate immunity during the first most dreadful disease of goslings healthy carriers. Due to its resis - of the disease, laboratory confirma - 6-8 weeks of life. and Muscovy ducklings. tance in the environment parvovirus tion is necessary. PCR and serology To achieve this, different methods Occasionally the disease accounts can persist in the buildings and on are the most commonly used labo - have been applied during the last for mortality of 70-100% in suscepti - poorly cleaned and disinfected sur - ratory tests for the confirmation of three decades. ble flocks when the infection occurs faces which results in transmission the clinical diagnosis. These include: at early age of life. between subsequent flocks. lPassive immunisation of newly GPV and MDPV differ in host Vertical transmission and egg shell hatched birds with convalescence or range and antigenicity, while geese contamination also plays an impor - Control hyperimmune serum. are fully resistant to MDPV infection, tant role in introducing the infection lActive immunisation of adult in Muscovy ducks both viruses can into disease-free flocks. Parvovirus The specificities of parvovirus infec - breeding geese and Muscovy ducks cause severe disease. It has been infects rapidly dividing cells; this is tion of waterfowl require the elabo - with virulent virus and inactivated shown that, even if a certain level of why clinical form of the disease ration of a coherent and efficacious vaccine. antigenic relation exists, there is a occurs only in young birds, up to vaccination strategy. The optimal lThe use of attenuated vaccine clear distinction between GPV and approximately six weeks of age. vaccination strategy must take into alone or in combination with inacti - MDPV. Nevertheless, infection with other account the presence or absence of vated one for the active immunisa - Cross-protection studies carried tion of both adult and young out in maternal antibody-free, sus - Table 1. Common clinical signs and pathological lesions in parvovirus animals. The attenuated vaccines can ceptible Muscovy ducklings indicated infection. confer good protection in young ani - that only bivalent vaccine containing mals but only when it is given to both goose and Muscovy duck par - CLINICAL SIGNS PATHOLOGICAL LESIONS birds with no or very low level of vovirus antigens provide adequate maternally derived antibodies to clinical protection against the two Acute form: Acute form: parvoviruses. waterfowl parvoviruses which can High mortality in young birds Dessication Historically, hyperimmune or con - cause disease in Muscovy ducks. In (before 10-14 days of age) Pale/dilated heart, myocardium valescence serum injected subcuta - addition, in mule duck (cross-breed Anorexia, prostration degeneration/necrosis, myocarditis neously in day-old goslings was used of Pekin duck and Muscovy duck) Paralysis in Muscovy ducks Hydropericardium and pericarditis to avoid heavy losses in flocks the so-called ‘short beak and Polydipsia (thirstiness) Hepatitis-nephritis-ascites complex exposed to parvovirus contaminated dwarfism syndrome’ have been Enteritis (profuse white diarrhoea) Sero-fibrinous perihepatitis (Fig. 6) environment. reported where animals had strong Ocular and nasal discharge Catarrhal or fibrinous/haemorrhagic This technique was effective but growth retardation with smaller Diphtheroid plaques on the mucosal enteritis (Fig. 7) presented the risk of carrying over beak and shorter tarsus. surface of the oral cavity undetected infectious agents by the The diseases caused by waterfowl Chronic form: Chronic form: contaminated serum. Therefore, paroviruses are strictly age depen - Uneven flock, severe growth Myodegeneration serum for controlling the diseases is dent. In susceptible goslings and retardation by 5-7 weeks of age Sero-fibrinous pericarditis and hardly available any more and the Muscovy ducklings less than one Loss of feathers (Fig. 8) perihepatotis prophylaxis is based on vaccination. week of age 100% mortality may Ascites (‘penguin-like’ appearance) Non-purulent myocarditis Two main categories of vaccines occur, while the losses above this Pancreatitis can be distinguished: live and inacti - age are decreasing with the age. In Neuritis and encephalomyelitis vated vaccines. l birds with impaired immune system (only in Muscovy ducks) Live vaccines contain attenuated the infection may cause significant goose parvovirus which can stimu -

24 International Poultry Production — Volume 19 Number 4 Fig. 9. Hemorrhagic enteritis in goose with polyomavirus infection. Fig. 10. Visceral gout in chronic form of HNEG. late rapid immune response and tion of breeders against parvovirus protect goslings and ducklings in all develop normally and then suddenly protection in maternal antibody-free has two objectives: their life against both the early and die with no premonitory signs. animals. MDA, even at a very low lTo protect the breeders from the late forms of the disease. In Other animals develop clinical level, is able to neutralise the live infection, and in this way prevent order to extend the protection after signs that include ataxia, tremors of vaccine thus preventing it to stimu - virus transmission to the progenies. the maternal antibodies decline to the head and neck, subcutaneous late immune-response. lTo supply the progenies with pas - unprotective level, the vaccination of haemorrhages and the excretion of lInactivated vaccines (also called sive immunity. goslings and ducklings before they blood-stained faeces. However, ‘killed’) contain the whole par - Breeders transmit protective reach 7-10 days of age is essential to once the clinical signs develop the vovirus antigens either in the mono - maternally derived antibodies stimulate active immunity in face of animals die rapidly. Geese, which valent (goose parvovirus) or bivalent (MDA) to the offspring through the still persisting maternal antibodies. recover from HNEG are supposed (both goose and Muscovy duck par - egg yolk. The level of MDA deter - To achieve a stronger and more to be persistently infected. vovirus) form. mines the level of protection (mor - durable immune response a booster The most frequent and character - Most of the parvovirus vaccines bidity and mortality) of goslings and vaccination (around 2-3 weeks of istic gross and histopathological available on the market are attenu - ducklings in case of field virus infec - age) is also recommended. lesions are summarized in Table 2, ated live vaccine and contain only tion. Knowing the level of maternal These can be done only by the use Figs. 9 and 10. goose parvovirus. antibodies in the day-old birds is fun - of inactivated, high antigen content Since the isolation of GHPV in The advantage of live attenuated damental to establish adequate vac - vaccine. many cases is very difficult or not vaccines is the fast onset of immu - cination strategy. possible, the PCR test for the detec - nity in susceptible birds, however A positive correlation has been tion of polyomavirus nucleic acid is the induction of immunity by live demonstrated between the number HNEG virus infection the only practically available method vaccines is very much dependent on of immunisations of breeders with to confirm diagnosis on an etiologi - the presence of circulating maternal inactivated vaccine and the amount Haemorrhagic nephritis enteritis cal basis. The GHPV-specific DNA antibodies to parvoviruses at the of transmitted maternal antibodies, virus infection of geese (HNEG) is could be detected in various organ time of vaccination. When using live including level of MDA, persistence characterised by high morbidity and samples including kidney, liver, vaccine at young age it is a regular of MDA in the young birds and pro - mortality rates in geese from 3-10 spleen, lung, bursa of Fabricius and observation that the presence of tection offered by the passive immu - weeks of age. Since its first report in intestinal contents from natural passively acquired antibodies inter - nity. 1969, several outbreaks with an epi - cases of the disease. feres with the development of an MDA may persist in goslings and zootic pattern have been reported Commercial vaccine against GHPV active immune response. ducklings at a relatively high level in almost all major goose breeding has not been available until now, On the other hand inactivated vac - which protects them from clinical countries. partially due to the difficulties in the cines with high antigen content are disease for approximately 2 to 3 Although HNEG has been well propagation of the GHPV in embry - able to induce active immunity and weeks. characterized at the clinical level and onated eggs and cell cultures. protection in face of maternal anti - Moreover, MDA levels after vacci - recognised as a viral disease many Therefore, the focus of GHPV vac - bodies. nation of breeders with traditional years ago, its causative agent has cine development turned to subunit The disadvantage of the inacti - live vaccines show an inevitable het - remained unknown until 2000, when vaccines. vated vaccine is the relatively slow erogeneity (low/high MDA). evidence was presented that the dis - The immunogenic antigen VP1 of immune response. The immunisa - Optimal vaccination strategy must ease is caused by a polyomavirus. GHPV was recently successfully Based on phylogenetic analysis, it expressed in both insect cells and Table 2. Frequency of characteristic gross and histopathological was concluded that the causative yeast. It was also demonstrated that lesions in HNEG. agent of HNEG is closely related to in both expression systems, VP1 but clearly distinct from other poly - alone or in combination with VP2, Acute Subacute omaviruses, likely representing a dis - forms virus-like particles (VLP), and cases cases tinct virus species named goose this as an antigen could be used in

Oedema in the subcutaneous a haemorrhagic polyomavirus. the development of vaccines and tissues and ascites +++ ++ The majority of the outbreaks serological tests. Hydropericardium ++ ++ occur between 3-6 weeks of age, Haemorrhages in the subcutaneous tissues +++ -/+ but sometimes much younger (four Haemorrhages in the brain ++ - days old) or older birds (17-20 Circovirus infection Anaemia + ++ weeks old) can be affected. Catarrhal enteritis ++ ++ The mortality can vary within a Relatively little is known about the Hemorrhagic enteritis +++ -/+ huge range (4-67%) and can con - diseases with which avian member Liver degeneration ++ ++ tinue for extended periods (1- 2 of the genus Circovirus are associ - Zonal hemorrhagic tubulonecrosis +++ +++ months), or with an interruption of ated. Avian circovirus infections Visceral gout - -/++ several weeks, i.e. two separate show certain common features. a: + = slight, ++ = moderate, +++ = marked, - = negative mortality peaks could be observed. They are seen in birds during the Animals in infected flocks generally Continued on page 26

International Poultry Production — Volume 19 Number 4 25 Continued from page 25 to be regarded as an option for dis - first months of life. Developmental ease control. and/or feathering disorders pre - On the grounds that for vaccine dominate the clinical signs. manufacturing purpose an efficient Damage to the lymphoreticular tis - antigen production system is sue is expected to impair both required and that circoviruses can - humoral and cellular immune func - not be grown by conventional cul - tions. Circovirus-induced immuno - turing method and are difficult to suppression enhances the inactivate, it is reasonable to expect pathogenicity of coinfecting agents. that a subunit vaccine based on the The course and outcome of the expression of virus protein by infection depend on the concurrent recombinant DNA-technology infections present and other predis - would be the target for vaccine posing factors. Subclinical infections development. I seem to occur that may cause con - siderable economic loss. Fig. 12. Globular or botryoid, One common feature of circovirus basophilic intracytoplasmic infection is that these viruses invade inclusions within macrophages in lymphoid tissue that may lead to the bursa of circovirus infected immunosuppression. Fig. 11. Lymphocytes depletion and cystic atrophy in the bursa of goose. Circovirus infection of geese and Fabricius of circovirus infected goose. ducks was first described in Germany by Soike et al (1999) and They are commonly observed in Knowledge of the genome Hattermann et al (2003) respec - the bursa of Fabricius (BF) and may sequences of goose and duck cir - tively. range from lymphofollicular hyper - coviruses allowed the development The commercial goose and duck plasia to lymphoid necrosis, lympho - of diagnostic tests such as PCR. farms in which circovirus was diag - cytes depletion, and cystic atrophy Molecular epidemiological results to nosed, exhibited growth retarda - (Fig. 11). date indicate that different avian tion, feathering disorders and The frequent detection of globular species are infected by different cir - increased mortality due to sec - or botryoid, basophilic intracyto - coviruses, suggesting that cir - ondary infections with Riemerella plasmic inclusions within macro- coviruses are host-specific. anatipestifer and Aspergillus fumiga - phages appears to be a character- Attempts to prevent and control tus. istic feature (Fig. 12). diseases caused by circovirus are The main histological changes Circovirus infections are diagnosed very limited. associated with circovirus infection on the basis of feathering abnormali - Given that infections with cir - in waterfowl species are those of ties, histology of BF, and demonstra - coviruses are likely to be prevalent the primary and secondary lymphoid tion of virus antigen or the nucleic and these viruses are highly resistant tissues. acid. to inactivation, eradication is unlikely

26 International Poultry Production — Volume 19 Number 4