Buffalopox: A Zoonotic Pathogen of Buffaloes
Gnanavel Venkatesan1, Sabarinath T1, Amit Kumar, Aditya Sahoo, Ajayta Rialch, V. Balamurugan, Raj Kumar Singh and V. Bhanuprakash1
Indian Veterinary Research Institute, Mukteswar 263 138, Nainital District, Uttarakhand, India.
Current address: 1Indian Veterinary Research Institute, Bengaluru campus, Hebbal, Karnataka 560024, India
Introduction
Buffalopox virus (BPXV) is the etiological agent of buffalopox, which was recognized by the FAO/WHO Joint Expert Committee on Zoonosis as an important zoonotic disease. Buffalopox was first reported in Lahore in undivided India in 1934. The first isolation of the virus was made in northern India in the year 1967 and the virus continued to cause sporadic outbreaks in Asian buffaloes (Bubalus bubalis) in Bangladesh, India, Indonesia, Nepal, Pakistan, Egypt, Russia, and Italy. The disease has become an emerging contagious disease with high morbidity upto 80% among affected domestic buffalo and cattle. Unlike in the previous years, generalized forms of the disease are now rare. However, there are severe local forms of the disease affecting the udder and teats, leading to mastitis thereby undermining the productivity of milk animals. Until recently, BPXV was considered host specific infecting only buffaloes but biological transmission of BPXV (BP4 strain) in cow calves have been reported. Reports of infection in humans maintaining close proximity with pox-affected buffaloes, attendants and milkers has been reported from India and Pakistan making this disease an occupational hazard for humans. The emergence of a pathogenic BPXV, which can spread efficiently from human-to-human, should be considered an immediate public health risk.
Virus Characteristics:
BPXV is resistant to ether but sensitive to chloroform, bile salts, pH and heat. Complete loss of infectivity of strain BP4 (Buffalo pox virus reference strain) has been reported at 56°C in 90 min, while strain BPH-80 (BPXV isolated from an outbreak in 1980 in Hisar) showed a drop in infectivity titre of log10 2.74 at 56°C in 30 min and complete loss at 56°C in 60 min. The BPH-80 strain of BPXV, though sensitive to heat, were able to produce pock lesions on CAM at 40.5+0.5°C, whereas the BP4 strain of BPXV failed to produce lesions. However, both these viruses (BP4 and BPH-80) produced pock lesions at 38+0.5°C.
BPXV is a member of the genus Orthopoxvirus, subfamily Chordopoxvirinae, family Poxviridae. BPXV resembles vaccinia virus (VACV) in terms of its size, shape, structure, physico-chemical properties and autonomous replication. Studies have indicated that the mature virus particle is brick-shaped measuring 280–330 nm × 200–250 nm in size. Various developmental stages of the virus in chorioallantoic membrane (CAM), including the modes of release of C- and M-forms of mature virions, are probably analogous to those of VACV. BPXV replicates in a wide range of cells. Cell cultures of bovine and monkey origins are most frequently used for virus propagation, accompanied by a cytopathic effect. Whole-genome Restriction Fragment Length Polymorphism (RFLP) studies have indicated genetic similarity between VACV and BPXV.
Epidemiology:
In India, buffalopox has mainly been recorded in young and old buffaloes during the epidemics. However, cattle have also been occasionally affected in epidemics which occurred in India. In an outbreak which occurred in various parts of Egypt, the spread of disease was rapid in buffaloes but cows, sheeps and goats in the same areas remained unaffected. Biting flies such as Lyperosiaexigua, Musca crossirostris and Musca vicina aggravated the sores. Therefore, it was postulated that flies may be involved in mechanical transmission. Transmissibility of BPXV was experimentally studied in a number of animal species, which revealed a wide host range, viz. buffaloes, cows at high dose of virus, guinea pigs and suckling mice (BALB/c and Swiss white strains). Strain BPH-80 produced pox lesions in rabbits, 6-week old mice, cow and buffalo calves. Sheep, goat, fowl and adult mice (BALB/c and Swiss white) were refractory to experimental BPXV infection. BPXV infects primarily buffaloes but can also cross species barriers and infect humans (milkmen and researchers) handling either the infected animals or the virus itself as is evident from many outbreaks.
Clinical Manifestations:
Buffalopox may be localized or generalized with mild to severe disease associated invariably with mastitis in almost 50% of the affected animals. Experimental inoculation by intradermal route of female buffaloes with Egyptian BPXV led to local erythema and cutaneous eruptions throughout the body with complete recuperation from the disease within a month. The skin lesions were more prominent on the udder, the base of the ear and other less hairy areas like the inguinal region. Otitis has also been reported due to secondary bacterial complications.
Pathogenesis:
Buffalo calves inoculated with BPXV by intra-dermal route showed increased temperature and localized skin lesions at 12 days post infection. BPXVinoculated in lactating buffaloes produced only localized lesions on the teats and udder without generalization. Complete protection against BPXV was demonstrated upon challenge. The in-contact control buffalo did not show pock lesions although it had a rise in body temperature. Likewise, BP4 strain produced typical skin lesions, nasal discharge and diarrhea in buffalo calves uponintra-dermal inoculation. Virus could be recovered from internal organs between 5 and 9 days post infection and from the skin after 10 days post infection and the disease lasted 13–15 days
Zoonotic Importance:
The Joint Expert Committee on Zoonosis emphasized that the mode of transmission of buffalopox to human subjects and other epidemiological features appear similar to cowpox. Human beings including smallpox-vaccinees contract infection upon close contact with buffalopox virus infected animals, but the extent of disease is greater in non-immunized individuals. The lesions are mainly confined to the hands, forehead, face, buttocks and legs (Fig. 1). Occasionally, lymphadenopathy has also been recorded. Milking of affected animals is one of the major modes of spread. The recent reports of detection of antibodies in disease free humans could be an indication of sub-clinical infection which might lead to exposure of the general population to BPXV.
Diagnosis:
Although various serological assays have been developed for diagnosis of buffalopox including AGID, counter-immunoelectrophoresis (CIE), Serum neutralization Test (SNT), ELISA and immunoperoxidase test (IPT), these tests fail in accurate diagnosis of the disease because of antigenic cross-reactivity. Conventional serological methods have limitations in identification and differentiation of Ortho Pox Viruses (OPVs). PCR and real-time PCR using targeting A-type inclusion body, DNA polymerase and C18L genes have been optimized and evaluated using known BPXV isolates and suspected field clinical samples. Primers for the C18L gene of OPXV were used in conventional PCR, duplex PCR, and real-time PCR for the detection and differentiation of BPXV from OPXVs, which amplify a 368 bp PCR product unique for BPXVs. In duplex PCR, using these primers together with those for the DNA polymerase (Pol DNA) and OPXV species, amplified only a 96 bp amplicon of the Pol DNA, whereas BPXV amplified both the 368 bp and 96 bp PCR products (Fig.2). Earlier, amplification of full-length A type inclusion (ATI) gene is also useful in the differentiation of OPVs. Also, characterization of genomic DNA of BPXV and camelpox virus (CMLV) employing DNA amplification fingerprinting by RAPD-PCR is used for differentiation of BPXV from CMLV.
Prevention and Control:
In countries such as India where the buffalopox is endemic and animal movement is difficult to restrict, disease control becomes complicated. The problem is compounded by lack of precise diagnostics and prophylactics.Further, the contamination of buffalo meat for export is another problem. The social belief, cultural issues and economic considerations prevent India from having a slaughtering policy for cattle. In the absence of suitable immunopropylaxis and restriction on animal movement, employing quarantine measures such as segregation of the infected animals from rest of the herd is the only means of containing the spread of infection. In IVRI, Mukteswar, a live attenuated vaccine was prepared using Vero cell-adapted BPXV (VIJ96) and compared with the already available reference strain (BP4) vaccine. The currently developed vaccine is found safe, efficacious and potent by experimental and limited field trials and is under technology transfer process. Currently, no licensed specific antivirals are available for the treatment of BPXV infections in humans and animals. Control of peridomestic rodents is equally important to curtail the virus transmission to domestic animals as observed in VACV epidemiology.
Selected References:
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Singh R.K., Balamurugan V., Hosamani M., Kallesh D.J., Bhanuprakash V. Sequence analysis of C18L gene of buffalopox virus: PCR strategy for specific detection and differentiation of buffalopox from orthopoxviruses. J. Virol. Methods. 2008;154:146–153.
Fig. 1: Clinical case of buffalopox in buffalo and humans showing lesions on teats (buffalo) and hands (human)
Fig. 2: Duplex PCR detection of BPXV DNA using C18L and DNA polymerase genes showing 368 bp and 96 bp products for BPXV and only 96 bp for other OPXVs in agarose gel electrophoresis
https://www.pashudhanpraharee.com/successful-treatment-of-buffalo-pox-like-lesions/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7558879/
