Description
Anaplasmosis is a form of 'tick fever' in cattle, also known as yellow bag or yellow fever. It is an infectious disease of the red blood cells caused by the rickettsial bacteria Anaplasma marginale. Most commonly transmitted by ticks, A. marginale causes disease primarily in cattle.
Other domestic and wild ruminants can be infected, but clinical disease is uncommon.
Anaplasmosis is a provincially notifiable disease for:
- cattle and yaks
- sheep and goats
- domestic and wild cervids
- farmed and wild bison
- ruminant animals residing in a zoo
Anaplasma ovis, the agent of ovine anaplasmosis, may cause mild to severe disease in sheep, deer and goats, but is not infectious for cattle.
How to report
If you suspect anaplasmosis in your herd, call your veterinarian within 24 hours.
Effective April 1, 2014, anaplasmosis in ruminants is no longer a federally reportable disease. It is now listed as a provincially notifiable disease under Alberta's Animal Health Act and must be monitored.
This means veterinarians must notify the province of suspected cases, and diagnostic laboratories must report suspected or confirmed cases to the Canadian Food Inspection Agency (CFIA). The CFIA does not respond to anaplasmosis cases detected on farms.
All suspected or confirmed cases must be reported to the Office of the Chief Provincial Veterinarian (OCPV) within 24 hours:
Hours: 8:15 am to 4:30 pm (open Monday to Friday, closed statutory holidays)
Phone: 780-427-3448
Toll free: 310-0000 before the phone number (in Alberta)
Fax: 780-415-0810
Clinical signs
Cattle of all ages can become infected, but severity of disease is age dependent.
Calves – can become infected but are generally resistant to clinical disease up to 6 months of age. From 6 months to 1 year of age, they can develop mild illness. After infection, calves can become asymptomatic carriers of the disease.
Cattle 1 to 2 years of age – can develop acute clinical disease, but it is rarely fatal. Signs include fever, going off feed, rapid shallow breathing, reluctance to walk, and pale mucous membranes.
Cattle older than 2 years of age – can develop acute clinical disease followed by sudden death. Fatality rates can range from 30 to 50% in animals that are first infected after 2 years of age.
Cattle with anaplasmosis may show the following clinical signs:
- sudden death
- severe anemia
- weakness
- fever
- respiratory distress
- loss of appetite
- depression
- constipation
- rapid decline in milk production
- jaundice
- abortion
- hematuria (blood in the urine)
Diagnosis
The presence of A. marginale may be confirmed by identifying the organism in a stained blood smear from a sick animal.
Whole, un-clotted blood and serum can be tested for the presence of the microorganism.
Pathological examination of fresh and fixed tissues will assist in ruling out other causes of death.
Pathological lesions
Animals that have died due to anaplasmosis may show:
- pale to yellow tinged (jaundice) mucous membranes
- thin watery blood
- enlarged soft spleen with prominent follicles
- enlarged liver with yellow-orange discoloration
- gall bladder distension with thick green-brown bile
- brown hepatic and mediastinal lymph nodes
- epicardial and pericardial petechia
- ecchymotic hemorrhages
Diseases with similar clinical signs
- Bacillary hemoglobinuria
- Chronic copper poisoning
- Any cause of hemolytic anemia, (for example: cold water intoxication, onion poisoning, postparturient hemoglobinuria)
- Leptospirosis
- Grazing of Brassica sp. (canola, kale, turnips, cabbage)
- Eperythrozoonosis
- Babesiosis
Where it’s found
While anaplasmosis is endemic in tropical and sub-tropical regions of the world, Canada – including Alberta – has experienced sporadic cases.
This is because infection with A. marginale occurs only occasionally in temperate climate areas where environmental conditions favour the survival of the ticks that carry the micro-organism.
There is higher prevalence of anaplasmosis infection and disease in many southern states of United States, Australia, central and south America, Africa and southern Asia.
Wildlife may also become infected with A. marginale. While they do not show signs of disease, they may act as a reservoir for the bacteria.
Anaplasma centrale is a less pathogenic but closely related organism. It has never been reported in North America. The organism is used as a live vaccine for cattle in several tropical and sub-tropical countries.
How it spreads
Primary modes of transmission
Ticks
Ticks are biological vectors of A. marginale and the most common route of transmission. Amplification of the infective organism occurs in the salivary glands of ticks.
Infected ticks can spread the A. marginale bacterium to susceptible animals. The bacterium then infects red blood cells causing their destruction and, as a consequence, severe anemia in cattle. Infected animals remain persistently infected carriers for life and are reservoirs for the organism in the herd.
Since ticks are the most common route of transmission, outbreaks of anaplasmosis are usually seasonal. Outbreaks occur during or immediately after the tick breeding season, which usually occurs in the spring.
Species
In North America, A. marginale can be transmitted by the Dermacentor species of ticks, including the 3-host ticks:
- Dermacentor andersoni (Rocky Mountain wood tick)
- Dermacentor variabilis (American dog tick)
- Dermacentor occidentalis (Pacific Coast tick – not present in Canada)
The 1-host tick Dermacentor albipictus (winter or moose tick) can also transmit the bacteria.
D. andersoni generally feed on larger mammals such as horses, cattle, moose, deer, mountain goat and elk. The tick is the predominant biological vector for genetic strains of A. marginalein the northwestern US.
D. andersoni has been reported from southern British Columbia eastwards into Alberta and extending into Saskatchewan. East of 105_ longitude, it is replaced by D. variabilis.
Mechanical transmission
Mechanical transmission occurs by direct inoculation of cattle with blood-contaminated hypodermic needles and surgical or dehorning instruments. Horseflies (Tabanids spp.) may mechanically transmit the bacteria on their mouthparts after taking a blood meal from an infected animal. Pregnancy checking using the same glove for many animals may also transmit A. marginale.
Transplacental transmission
Transplacental transmission occurs after acute infection of the cow during its second to third trimester of gestation. Infected red blood cells from the infected cow move across the placenta to the fetus.
Risk to humans
There is no human health risk associated with anaplasmosis.
Human anaplasmosis is caused by a related bacterium, Anaplasma phagocytophilum, also transmitted by bites from infected ticks. Black-legged ticks (Ixodes spp.), which are present in Alberta, are the primary vectors of A. phagocytophilum. This bacterium is present worldwide but seems to cause the disease called tick-borne fever in domestic and wild ruminants in Europe.
Prevention and control
Once anaplasmosis is in the herd, it is costly to treat and difficult to control. Infected animals remain persistently infected carriers for life and are reservoirs for the organism in the herd.
Cattle, bison and elk producers play an important role in keeping their animals healthy, and are encouraged to talk to their veterinarians about the disease.
Treatment and vaccines
At this time, no vaccine or treatment for anaplasmosis have been approved for use in Canada. There is a commercially available vaccine against anaplasmosis in the United States, but it does not prevent the disease; it only reduces death loss.
Importing animals
Producers must comply with all import requirements when purchasing animals from outside of Canada. This may include testing of animals for other diseases prior to import, depending on the country and location of origin.
For information on federal import policies, see Import policies: live animals (CFIA).
When importing animals, owners should consider:
- consulting their herd veterinarians for advice to prevent introducing the disease in their herds; it is the buyer's responsibility to ensure purchased animals are free of anaplasmosis
- treating animals with an effective acaricide to kill all ticks that may be on the animal before introducing the animals in the herd