Reported outbreaks of goat pox worldwide yields differing mortality rates with 7% in Sudan , 21% in Iraq  and 30% in India . In this study, a much lower mortality rate was found despite a rather high morbidity rate high probably owing to the study population comprising less of the 3–6 months old goats. It has been shown that maternal antibody for goat pox is maintained for about 3 months and those older than 6 months that survived an infection will have life-long immunity [8–9]. This phenomenon explains the susceptibility of those in the 3–6 months old  which should yield higher morbidity rate. However, since the group of animals under this group is quite low, the mortality rate has failed to surpass those of other groups.
The number of death animal during the outbreak depends on the virus virulence, size of the population and their susceptibility and on the basic reproductive number . However, these rates may vary depending additional factors including breed  and the most notably the herd immune status . Recently published data showed that case fatality rate of goatpox disease ranged from 21.4 % to 60 % [13–15]. Likewise, the high fatality rate in the present study undermined the need for a much more effective control of goat pox along with the requirement to vaccinate at least susceptible herd or in endemic areas. However, the difficulty to implement such health programs in Vietnam is explained below.
Based on seroprevalence,  reported a morbidity rate in nomadic goat herds in Punjab to be about 23%. It is not suprising to see a higher infection rate in the extensive system as previously reported . Unfortunately, this rearing method is popular to poor farmers in midland and mountainous areas in Vietnam who could not afford to spend on a standard health management. Goats under the extensive system forage freely in a wide area exposing them increase chances to be exposed to the virus. These goats might have also been exposed to lesser domestication, maintaining many of the behavioural traits of the wild types such as aggressiveness [17–18]. Furthermore, goats especially under the extensive system being naturally aggressive  predisposes the body to injuries making easier access of the virus when inoculated. This is an added problem since most of the goats were not dehorned (due to financial constraints) making injuries prone to infection during a fight. On the contrary, the low infection rate under the intensive system is due to a much proper disease control program that has minimized spread of the virus within the herd.
Undoubtedly, defining the vulnerable period of infection is one of the most important measurement to be known for an effective disease management . In the study presented here, the most susceptible age were goats of 3–6 months old which conforms to findings of  and  who found that the chance of infection chance in the young was 2.2 times greater than that of an adult. However, contradictory results were seen if infection rate was based on seroprevalence. Fentie et al.  demonstrated a low infection rate in older animals although this appeared to refute earlier published findings . Nevertheless, in the latter study , age groups were not clearly defined which may have led to a less homogenous groupings. Additionally, the collected samples from slaughter house, tanneries and hide markets where the likelyhood of the proportion of kids to be devoid . The age grouping the study presented here was based on the main purpose of meat goat breeding in Vietnam. The indigenous and mixed breed of Vietnamese goat attained a market weight of 25 to 30 kilograms at 6 months old age, justifying a 3 month interval being chosen.
Recognising the key salient clinical signs is key factor for field diagnosis of goat pox . The foremost marked as seen in this study too were depression and being much more severe in kids [22–23] accounting for systemic signs of pyrexia. About 85% of affected animals showed varying degrees of anorexia associated with the development of lesions on mucus membrane of the face. The lesion commences as red patches around the mouth, nose and eyes which later swelling into a papule. These papules trigger lacrimal, nasal and saliva discharges. Respiratory distress and secondary bacterial pneumonia are predominant in kids which could not survival malignant stage [6, 24–25]. In adult goats, the ulceration of papules renders difficulty for digestive and breathing activities which in turn worsen productive performance. There are goats with conjunctivitis, corneal opacity and blepharitis had been recorded which animals emulated the acute phase pox disease . The development of pox lesions is observed over the animal body especially hairless areas (face, pinna of the ears, udder, genital, anus, under the tail). The red patches turn to hard rubbery papules and become vesicles after 3 to 4 days. Necrotic papules formed pustular as the result of thrombosis and localised ischaemia. Dark hard scabs are formed by the remnant of necrotic papules [6; 25–27].
In this study, for all positive cases, the clinical and post mortem lesions were 100% present in the skin and lungs of affected goats. It is likely that owing to the epitheliotropic nature of the virus lesions were predominantly seen in the skin, lung and discrete sites within mucosal surfaces of oro-nasal and gastrointestinal tissues . As evidenced in this study and as reported earlier in similar studies, the role of skin and lung as a target organ  for the virus leads to much more deposition of the lesion in these tissues [29–30]. Beside darkened circumscribed pox lesions [29, 31], the entire lung are pale pink with loss of sponginess. Congested trachea contain blood or fluid-filled vesicles with involvement of the lymph nodes. As seen in the study presented here, calcified nodules are found the most abudant in large intestine (rectum) of goats that were mildly affected [21,32].
Histopathological findings in the study presented here were in accord to previous publications registering marked change in the epidermis. The degeneration of epithelial cells, hyperkeratosis, ballooning and degeneration of proliferating epithelial cells along with inflammation led to the desquamation of skin layers. Variable observation of lung microscopy include haemorrhage, congestion and thickening alveoli wall which resulted in narrowed alveoli. Secondary bacterial infection has invoked infiltration of inflammatory cells to affected regions of the lung [6, 33–34].
The PCR-based test is chosen regarding to its sensitivity and simplicity . The sensitive and simple PCR assay has confirmed caprine pox virus in the biopsy samples . Almost 80% of the samples were positive with amplicon size of 172 bp although no attempt was made to identify and differentiate of caprine pox virus [1, 22, 37–38]. However, the isolates from this study did not show much variation compared to those reported in China .
These findings boils down to the possibility of Vietnam’s aspiration to transform the future potential of goat farming into an industry. The local consumer prefers fresh chevon than frozen products due to food safety issues linked to the weakness of their cold chain system . Furthermore, goats apart from being a form of meat for the family and community it serves as a cash reserve for the poor farmer .
The current study also revealed most of the goat husbandry system is mainly extensive which may hamper the possibility to initiate goat production outside the mountainous areas. Likewise, as unveiled here, goats reared under the intensive system offers a better farming milieu for disease control which the farmer or nation should adopt to improve productivity. Nevertheless, nation should make formidable reforms to the livestock industry since goats in Vietnam are still (as found in this study) and in future will be reared by the poorer farmers halting an increase in goat population and productivity. This is even much more worrying especially with respect to a lack of herd health program (disease control). Thus, in order to bring the industry to greater heights, offsetting devastating disease like goat pox is mandatory. It is believed that these findings on goat pox will facilitate the government to continue working on improving disease identification and control to avoid hindrance in goat production.