Common Infectious Diseases of Small Ruminants and Their Prevention
Manoranjan Rout*, Jajati Keshari Mohapatra and Rabindra Prasad Singh
ICAR-Directorate of Foot and Mouth Disease, International Centre for Foot and Mouth Disease, Bhubaneswar – 752050, India
World Veterinary Day
The veterinary profession is the only profession in the world that is blessed with an ability to listen and realize the unspoken words of those who can never express their pains and sufferings. The world veterinary day is celebrated annually on the last Saturday of April every year to commemorate the veterinarians worldwide recognizing their work and immense contributions for the cause of animal health and welfare. This year the proud moment will be on April 30, 2022. The celebration of the day intends to sow the seeds of inspiration and enthusiasm in the young minds moving through the corridor of veterinary science simultaneously paving the way forward for research and developments in the field of veterinary science. On the eve of this world veterinary day, we thought to highlight some common infectious diseases of small ruminants prevalent in our country and their prevention with a hope that it can create an awareness among the poor farming community and may indirectly support their livelihood through improving and safeguarding the health of their animals from such important diseases.
Introducing the topic
Small ruminants e.g., sheep (Ovis aries) and goat (Capra hircus) were among the first animals to be domesticated. Sheep reportedly has its origin from four distinct wild sheep, e.g., Urial, Argali, Mouflon, and Aoudad, while goats have been originated from only one wild type, the Benzoar of Asia Minor and the Middle East. More than 850 breeds of sheep and more than 500 goat breeds inhabit across the globe. Sheep and goats are often reared in marginal conditions with scanty grazing and unfavorable climatic situations. Both the species being naturally hardy survive by grazing on less endowed community pastures in unused lands and sufficiently protect themselves against diseases. They play a vital role in sustainable agricultural systems supporting and ensuring the livelihood and earnings of the rural poor in Indian sub-continent. They are the dairy animals of the poor and hence popularly known as the poor man’s cow as they provide milk to the poor under low or negligible capital investment. More than 90% of small ruminants are owned by landless and marginal farmers in India, where the average goat milk yield is nearly165 kg/year. As per the most recent 20th livestock census conducted in 2019, the total sheep in India is 74.26 million and goat is 148.88 million (DAHD, 20th Livestock Census 2019, All India Report). India, Bangladesh and Sudan are among the countries considered as major goat milk producers in the world.
Common infectious diseases in sheep and goats in India
Common infectious diseases of small ruminants in India are foot and mouth disease (FMD), peste des petits ruminants (PPR), capripox, CCPP, anthrax, haemorrhagic septicemia (HS), enterotoxaemia, black quarter (BQ) etc, among which those with severe economic significance are covered below. Such diseases if controlled and prevented can indirectly improve the livelihood of the rural poor in the country.
Foot and mouth disease (FMD)
FMD is a highly contagious viral disease of small ruminants with a significant economic impact. It was the first disease for which the OIE could establish the official status recognition. Despite being known since long, FMD is still a threat to many farming economies in the world. The cause is FMD virus, an Aphthovirus of the family Picornaviridae. There are seven serotypes (A, O, C, Asia 1, SAT1, SAT2, SAT3) globally circulating in different countries worldwide, among which O, A and Asia 1 are prevalent in India. Small ruminants play an important role in the epidemiology and transmission of FMD. The outbreak of FMD in the United Kingdom has highlighted the importance of sheep in the epidemiology of the disease, although there have been numerous examples in the past where small ruminants have been implicated for the introduction of FMD into previously disease-free countries (Kitching and Hughes, 2002).
All excretions and secretions from the infected animals contain FMDV. Infected animals breathe out a large amount of virus that can infect other animals through the respiratory routes. The virus can spread through contaminated sheds where diseased animals are kept or animal transport vehicles; contaminated beddings, footwears or equipment used; infected animals newly introduced into a flock without the intervention of quarantine. FMD in small ruminants has an incubation period of about 3-8 days (Kitching and Mackay, 1994). Adult sheep and goats with FMD do not show clear clinical signs being frequently mild or unapparent for which it can easily be missed by the farmers or difficult to diagnose by the veterinarians. Moreover, the cardinal signs in infected sheep are mimicked by other diseases (Ganter et al., 2001). Small ruminants considered as the maintenance host for the FMD virus.
In sheep and goats, the most frequent first observable clinical sign is lameness. Though in adults the disease is not so fatal, it can cause high mortality in young animals due to myocarditis. The clinical signs in sheep and goats include high fever, salivation (not ropy as in cattle), decrease in food intake due to mouth lesions and drop in milk production, oral vesicles, interdigital spaces ulcers, lesions on the dental pad. Affected animals show reluctance to walk due to lesions in coronary bands and interdigital spaces and they may separate themselves from the rest of the flock. About 25% of the affected sheep do not develop vesicles and 20% have lesions only at one site or develop visible vesicles. Vesicles may also be observed on the teats especially of milking sheep and goats and rarely on the vulva and prepuce (Kitching and Hughes, 2002). Pregnant ewes may abort following the course of FMD.
For control and prevention of FMD, vaccination is the only feasible option in developing country like India. The vaccination has been routinely taken up by the Government of India under National Animal Disease Control Programme (NADCP) of course in large ruminants. But the same inactivated FMD vaccine can be given to kid or lamb and above the age of 4 months and be used at regular intervals of 6 months to prevent the disease in sheep and goat population.
Peste des petits ruminants (PPR)
PPR is considered to be the disease of major economic impact and has to be notified to the World Animal Health Organization (OIE) (Albina et al., 2013). The highly contagious nature of the disease poses a significant threat to the farmers by incurring severe economic loss. In many areas of India, small ruminant production and indirectly the livelihoods of poor farmers are threatened by PPR. It is estimated that one billion small ruminants or about 62.5% of global domestic small ruminant population is at risk of infection with PPR (Ahmed, 2020). More than 200 million small ruminants are at risk of PPR and the annual loss due the disease has been estimated at approximately INR 1,800 million (Venkataramanan et al., 2005). An estimate says an average of 1 out of every 3 small ruminants in India has previously been infected with PPRV and has subsequently got recovered from the disease.
PPR was first described in Ivory Coast of West Africa in 1942 and named as Kata, psuedo-rinderpest, pneumoenteritis complex and stomatitis-pneumoenteritis syndrome. PPR in India was first reported in sheep at Arasur village, Villipuram district of Tamil Nadu during 1987 (Shaila et al., 1989). The disease is caused by RNA virus e.g., PPR virus (PPRV), a small ruminant morbillivirus in the family Paramyxoviridae (Zakian et al., 2016). Clinically PPR is observed in both sheep and goats however, goats are more susceptible than sheep (Adel et al., 2004). Goats are severely affected while sheep undergo mild form. Severe loss is encountered especially in goats with morbidity and mortality rates sometimes approaching 80-100%. The virus is transmitted through direct contact between infected and healthy susceptible animals. Kids within 4 months to 1 year of age are most susceptible to the disease. Stressful confinement and restricted movement of animals due to rainy seasons in tropical countries affect the nutritional status predisposing them to PPRV infection. Climatic condition is also a major factor and outbreaks are most frequent during the rainy season or the cold dry season. In subtropical areas, the occurrence of the disease is more common during winter and rainy seasons.
The majority of farmers in India have small and marginal land holdings (IASRI, 2003). Small ruminants survive on free-range pastureland, shrubs and forest cover. Due to progressively decreasing pastureland and forest area, these animals have to travel long during the dry season in search of fodder and water. Migratory small ruminants have been observed in the sub-Himalayan region as well as in dry land areas in the states of Rajasthan and Gujarat. The nomadic animals during the course of migration often come in contact with local sheep and goat populations through the movement tracts from whom they may contract the virus. Such infected migratory animals may further transmit the virus to other susceptible local sheep and goats. The movement of animals therefore plays an important role in the transmission and maintenance of PPRV.
The incubation period varies from 2 to 10 days and in most cases the clinical symptoms start in 2-6 days. PPR in most cases is acute with fever lasting for 5-8 days. The affected animals shed the virus in exhaled air, tears, nasal discharges, secretions and excretions from natural orifices, coughing and in feces of infected animal about 10 days after the onset of fever. Transmission through ingestion and conjunctival penetration, by licking of bedding, contaminated feed and water troughs are also not uncommon. During close contact between animals PPRV is mainly transmitted by aerosol route through sneezing and coughing (Banyard et al., 2010). Infection can spread to kids through milk of infected ewes and does (Munir et al., 2013). The virus is shed from the intestine and is found in feces at the end stage of the disease approximately 10 days after the onset of fever (Zakian et al., 2016).
Typical clinical signs begin with a clear nasal discharge that gradually becomes greyish and sticky. Such discharge from the nose may remain mild or may progress to crusting exudates blocking nostrils inducing respiratory distress. Small erosive areas may be observed in nasal mucous membranes and the conjunctiva may be congested with matting of the eyelids. The oral mucous membranes may also be eroded due to necrotic stomatitis that starts as small necrotic focus on the dental pad/gum below the incisors. Necrosis may result in shallow irregular erosions in the affected areas of the mouth. At the height of development of oral lesions, most animals manifest severe diarrhea causing severe dehydration, emaciation and dyspnea followed by hypothermia and death occurs after 5 to 10 days of such clinical course. Subsequently, bronchopneumonia with coughing characterizes the later stage of PPR. Pregnant infected animals may abort. Secondary infections may be activated complicating the clinical course of the disease (Afera et al., 2014).
Similar to other viral diseases, vaccination is the only alternative to protect the animals and vaccination against PPR has been practiced in some states of India since 2002. Live attenuated PPR vaccines are effective and widely available. Live attenuated homologous PPR vaccine was developed at IVRI (Sreenivasa et al., 2000). Sheep and goats recovered from PPR or vaccinated with attenuated PPRV strain develop an active life-long immunity. Several homologous PPR vaccines with cell culture-attenuated strains are available (Saravanan et al., 2010). In India, PPR vaccines and fool-proof diagnostics have been developed and available for field use since long (Singh and Bandyopadhyay, 2015). A sandwich-ELISA (Singh et al., 2004a) for diagnosis of PPR in small ruminants and monoclonal antibody based competitive-ELISA (Singh et al., 2004b) for detection and titration of antibodies to PPRV have been developed. The s-ELISA kit developed at Division of Virology, IVRI, Mukteswar, India uses a MAb (4G6) directed against an epitope of N protein of PPRV (Singh et al., 2006) that is routinely used for detection of PPRV antigen in clinical specimens in India (Singh et al., 2004). Presently, 3 live attenuated PPR vaccines using lineage IV PPRV isolates (Sungri/96, Arasur/87 and Coimbatore or CBE/97 stains) are available in our country, of which Sungri/96 developed by IVRI, Mukteswar has undergone extensive field trials with satisfactory results.
Sheep pox and Goat pox
Sheep pox and goat pox, two endemic capripox infections are notifiable and pose a significant threat to small ruminant sector in India. Their etiological agents are sheep poxvirus (SPV) and goat poxvirus (GPV) under Capripoxvirus genus of the Poxviridae family. The diseases bear economical significance as they cause emaciation, weight loss, drop in milk production along with skin damage (Babiuk et al., 2008).
The SPV and GPV are mainly found in oral, nasal, or ocular secretions (Bowden et al., 2008). Transmission is facilitated either by direct contact through aerosols from infected hosts, or indirectly through the environment and infected vectors (Sprygin et al., 2019). Clinical signs can be mild, severe, or sometimes fatal. Varying degree of severity has been reported in goats of same age and breed, infected with the same strain (Babiuk et al., 2009). The disease is more serious in young animals than in adults. Usual signs include fever, enlarged lymph nodes, oculonasal discharge and eruption in skin and mucous membranes (Hurisa et al., 2018). Skin lesions begin as erythematous macules that harden further to form papules. The papules subsequently become pustules and scabs following tissues necrosis. These lesions are most often found in hairless areas of the animals, but in severe illness can spread all over the body. The lesions can ulcerate or necrose in the mucous membranes of mouth, nostrils and eyes. Lesions in the eyes and eyelids can cause conjunctivitis and blepharitis. Damage to the intestinal tract or respiratory system can lead to diarrhoea, emaciation, or coughing and pneumonia. Skin lesions heal slowly and can cause permanent scarring. A nodular form of skin lesion called ‘stone pox’ looking like nodules all over the skin has been implicated that further become necrotic, when the nodules break off and leave ulcerative lesions or scabs (Diallo et al., 2007).
Control and eradication of capripox depend on zoosanitary measures, early detection of outbreaks with movement restrictions and most importantly the vaccination. Live attenuated vaccines are mostly used to control capripoxvirus (Tuppurainen et al.., 2018). Several SPV/GPV strains attenuated by passages through different cell culture systems or on embryonated eggs are named on the basis of the place of isolation e.g., Jaipur (Kalra and Sharma, 1981), Uttarkashi (Das et al., 1978), Romania, Cairo, Chinese etc. Vaccination in India is carried out with Uttarkashi and Mysore strains (Hosamani et al., 2004). Animals above 4 months of age are vaccinated with the current homologous vaccines by intradermal or subcutaneous routes. Inactivated vaccines are advantageous allowing to make polyvalent vaccines are safe and stable.
Enterotoxemia (Over-eating disease/Pulpy kidney disease)
Enterotoxaemia, a toxico-infectious disease of acute and fatal nature is common in sheep and goats. Sheep enterotoxemia is caused by Clostridum perfringens type D, while the situation is less clear in goats by virtue of its limited studies in the species. The disease may occur in goats of all ages and animals with good health appears to be the most prone. C. perfringens type D being a normal commensal is found in small intestine in relatively low number. Under certain circumstances, e.g., sudden ingestion of protein and carbohydrate-rich feeds through various diets such as milk, milk replacers or green lush grasses permits more undigested starch to pass through the rumen to the abomasum and intestine where it helps in rapid proliferation of the bacterium. Proliferation of C. perfringens type D in association with decreased peristaltic movement stimulate the concentration of the epsilon toxin produced by the organism (Songer, 1996).
The affected animal becomes lethargic and anorectic. It exhibits signs of stomach-ache e.g., kicking the abdomen, frequent lying down and up, panting, lying on one side with frequent crying and diarrhoea. Due to the effect of the toxin produced by the bacteria affecting the brain the animal lies down on one side extending the legs and neck and head become extended turning towards the back. Kidney being one of the other target organs for epsilon toxin, the disease is called ‘pulpy kidney’ that has a diagnostic significance in ovine enterotoxaemia, while such renal involvement is not considered of diagnostic significance in caprine enterotoxaemia (Uzal and Songer, 2008). The onset of the disease is so rapid that most animals succumb without any premonitory signs.
Vaccination is one of the most important tools to control any toxico-infectious disease and similarly enterotoxaemia. The first dose of vaccination is given around 6-10 weeks of the age and then booster about 2 weeks later. Annual booster is recommended afterwards in order to maintain a higher immunity. Similarly, ewes are to be vaccinated 1-2 month prior to the lambing so as to avail higher antibodies levels in their colostrum.
Anthrax
Anthrax caused by Bacillus anthracis in small ruminants is manifested with septicemia, sudden death with characteristic oozing of tarry unclotted blood from the natural body openings. It has an incubation period of 3-7 days (ranging from 1-14 days). In herbivores, the clinical course ranges from per acute to chronic. The peracute form is characterized by sudden and rapid onset, staggering, dyspnea, trembling, collapse. A few convulsive movements may be observed in sheep or goat. Dark, tarry blood is evident from mouth, anus, nostrils and vulva of the affected animals due to the effect of fibrinolysin secreted by the bacteria. There is a sudden rise in body temperature and excitement followed by depression, respiratory or cardiac distress, convulsion and death in an acute form of anthrax. Blood gets discharged from natural orifices. The chronic form is characterized by localized subcutaneous edematous swelling, most often at the ventral neck, shoulders and thorax. As a mode of prevention and control of this fatal ailment, anthrax spore vaccine is administered to the susceptible animals at the age of 6 months for kid or lamb and followed subsequently once annually (in affected areas only).
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