The vulnerable dogs…
Blood-feeding parasites can transmit a variety of pathogens to dogs. These arthropods including ticks, fleas, flies and mosquitoes can transmit bacteria, protozoa, viruses or helminths to dogs which can lead to infections such as babesiosis, ehrlichiosis, leishmaniasis or heartworm disease. Some vectors such as ticks can transmit more than one pathogen. Besides, different Canine Vector Borne Diseases show similar clinical signs which, ultimately complicate the diagnosis and treatment.
Various factors predispose dogs to infections with two or multiple vector transmitted pathogens:
- Dogs living in areas that are highly endemic for several vector borne pathogens.
- Animals living predominantly outdoors thus facilitating enhanced vector transmission.
- Irregular or no use of ectoparasiticides.
- A suppressed immune response (due to old age, underlying infection or immunosuppressive therapy).
Ticks are one of the most important vectors that transmit CVBD as they harbor the largest number of different pathogens. Ticks are especially suitable for pathogen transmission, by attaching securely to their hosts and facilitating effective transmission of infectious pathogens over a couple of days. Many of the diseases caused by these tick-borne pathogens possess a wide variety of clinical features and share non-specific signs such as wasting, weight loss, fever and poor appetite or anorexia all making it a challenge to arrive at a definitive diagnosis.
In co-infections with pathogen that have different clinical signs, the extent to which different infections might influence each other’s pathophysiology is not clear.
The life-cycle of ticks…
Tick-borne pathogens are a cause of animal and human suffering. A large number of different pathogens are transferred from infected ticks to dogs following tick attachment and feeding. However, transmission of tick-borne disease agents does not appear to occur immediately when the tick begins feeding for the first time in a given life cycle. A reactivation period is required for the pathogens to begin replicating, migrate to or be activated in, the salivary glands and be transmitted to the host when the tick regurgitates excess fluid back into the bite wound.
In most tick-borne disease systems, an initial attachment and feeding period of at least 24-48 hours is thought to be required to allow reactivation of tick-borne pathogens and subsequent transmission. Time is required for e.g. the spirochetes to be activated, increase in numbers and migrate for the midgut to the salivary glands. Partially fed ticks will readily reattach to new hosts and resume feeding, similarly if a tick infected as a larva or nymph to one host and then moves on to the second host for next life cycle stage, faster transmission time is likely to occur.
Pathogens are transmitted to dogs by a variety of different species of hard ticks (ixodid) or soft ticks (argasid). The hard ticks, for example, Rhipicephalus sanguineus, commonly known as the brown dog tick, spend all three stages of its life cycle on dogs and require a blood meal prior to sexual maturation and mating. Ixodes spp. are responsible for transmitting Borrelia burgdorferi and Anaplasma phagocytophilum to dogs.
Canine infection occurs when salivary secretions form the tick contaminate the attachment site during ingestion of a blood meal, Adult R. sanguineus are capable of transmitting E. canis for at least 155 days following detachment from the host.
There is a need for a comprehensive control programme for vector borne pathogens, due to the new distribution patterns of vectors.
Prevention of arthropod bites is mainly achieved by preventing the attachment and thus further blood feeding, if possible. Broad spectrum ectoparasiticides with repellent properties such as the pyrethroid insecticide, are ideal compounds to achieve this goal, as they prevent the biting of different vectors like ticks, flies, fleas and mosquitoes and therefore minimise the host parasite interaction, thus decreasing the risk of disease transmission. A regular treatment with these compounds during the transmission period is crucial for the prevention of single and multiple canine vector borne diseases.
Prevention: Apart from babesiosis & borreliosis, there are no protective vaccines available to prevent dogs from the above-mentioned infections. To overcome this dilemma, pet animals (especially dogs) should be protected against ectoparasite infections in the first place. Besides husbandry measures, such as keeping dogs indoors in endemic areas, effective prophylaxis may also be provided by regular use of ectoparasiticidal products with a repellent, as well as insecticidal & acaricidal action.
(Contributed by Dr Mandar Deshpande, Business Manager – Companion Animal Products, Bayer Pharmaceuticals Pvt Limited)