Camelpox is a disease of camels caused by the camelpox virus (CMPV) of the family Poxviridae, subfamily Chordopoxvirinae, and the genus Orthopoxvirus. It causes skin lesions and a generalized infection. Approximately 25% of young camels that become infected will die from the disease, while infection in older camels is generally more mild. Although rare, the infection may spread to the hands of those that work closely with camels.
Cause
The camelpox virus that causes camelpox is an orthopoxvirus that is very closely related to the variola virus that causes smallpox. It is a large, brick-shaped, enveloped virus that ranges in size from 265–295 nm. The viral genetic material is contained in a linear double-stranded DNA consisting of 202,182 tightly packed base pairs. The DNA is encased in the viral core. Two lateral bodies are found outside the viral core, and are believed to hold the enzymes required for viral reproduction.
The camelpox virus most often affects members of family Camelidae. However, recent studies show that the disease can be transmitted to both humans and arthropods.
Transmission
The camelpox virus is spread in three ways: direct contact, indirect contact, and insect vectors.
In direct contact infection, a camel becomes infected after direct contact with an infected camel.
In indirect contact infection, a camel becomes infected after contact with an infected environment. The virus is spread through milk, saliva, ocular secretions, and nasal secretions, and has been shown to remain virulent outside of a host for four months.
The camelpox virus has been isolated from camel ticks (Hyalomma dromedarii) removed from infected animals. It is believed that the ticks can transmit the disease from camel to camel. This theory is supported by increases in Camelpox infections immediately following heavy rains, during which the camel tick population increases greatly.
Transmission of camelpox to humans was confirmed in 2009 when camel herders in India presented with infections of the hands and fingers. Although other cases of human infection have been reported, no other cases have been verified. Due to the close contact between camels and their human handlers in much of the world, it is believed that camelpox is transmitted to humans via direct contact.
Replication
The orthopox virus that causes camelpox behaves very similarly to the virus that causes smallpox. After the virus attaches to a host cell, it injects its viral core (the shell containing its DNA) into the cell's cytoplasm. The virus carries DNA polymerase which is used to transcribe its genes. Eventually, the viral core dissolves, and the genetic material is bare within the cytoplasm. When all of the structural proteins have been produced, viral assembly takes place. The newly formed virus particles can be released during cell lysis, or they can derive a host cell produced membrane and be released via budding.
Signs and symptoms
The incubation period of camelpox is between 3 and 15 days. The resulting infection can be classified as acute or generalized. Generalized infections are usually found in camels over the age of three, and are characterized by swollen lymph nodes, fever, and the development of skin lesions. The lesions begin as papules, but develop into pustules. These external symptoms usually begin on the head and neck, but eventually spread throughout the body, being especially concentrated on the limbs and genitalia. Without treatment, the animal will generally recover from the infection in 4 to 6 weeks.
Acute infections are usually found in camels under the age of three, and result in mild to severe systemic infections. In addition to the symptoms that accompany a generalized infection, these animals experience internal lesions along the lining of the mouth, and respiratory and digestive tracts. They also experience loss of appetite and diarrhea. A large proportion of camels acutely infected with camelpox die, although death is often attributed to a secondary infection.
Camelpox infections in humans result in mild skin lesions on the hands and fingers. Reports have been made that the lesions can be found on the mouth and lips if the patient drank milk from an infected camel, but these symptoms have not been confirmed.