Continued
Transmission
There are several different routes that an infectious agent (germ) can take to enter a new host and make it ill. Let’s look at some of the possibilities:
(i) Contact with body secretions/excretions (eg tears, saliva, semen, urine, faeces).
(ii) Via inhalation of air that contains germ-ridden droplets.
(iii) Sexual transmission during coitus (the sex act)
(iv) Contact with spores in the soil which enter the host via a break in the skin.
(v) Transmission by biting insects/parasites.
(vi) Ingestion of contaminated material.
(vii) Introduction of the germs by human action (not lastly by medical personnel who use unclean instruments or who invade the body in an unhygienic environment).
(viii) Via the umbilical cord.
ad (i): In a calf pen, it is amazing to see how an infectious agent, present in the faeces during a diarrhoea episode, can be transferred from calf to calf. In a breeding kennel or in a home where several dogs are kept in close proximity to each other, a disease like Canine Parvovirus will move through a litter/group of unvaccinated puppies/adult dogs like a wild fire. The faeces splatters up and infects the dogs pretty easily if the mess hits the eyeball or the mucous membrane lining of the mouth. That’s why sick puppies/dogs should be isolated from the rest of the litter or kennel mates.
In the case of Leptospirosis which is transmitted by carrier rats, it is the latter’s saliva and urine which primarily contaminate the leftover food and water.
ad (ii): The Feline Respiratory Disease Complex, better known (incorrectly) as ‘Feline Influenza’ is a good example of a transmission of the infectious agent (virus) by aerosol droplets. The afflicted animal sneezes and, during that explosion, the released virus-infected droplets are carried by air to a susceptible animal.
ad (iii): In large animal medicine, there are several examples of sexually transmitted diseases (eg Brucellosis, aka, Contagious Abortion, Vibriosis, Epivaginitis, etc). In companion animal medicine, the most common venereal diseases exhibit themselves as vagina/penis tumours and as vaginitis cases in dogs and, to a lesser extent, cats.
After every mating season, veterinarians have their hands full, excising huge, bleeding, ugly looking, cauliflower–like growths which protrude from the vagina. Although these tumours have been linked with hormonal imbalances, there seems not to be a unanimous opinion on the role of the actual sex act in the transmission of this disease. However, empirical observation of known studs with tumours around their penises reveal that often their mates show vaginal tumours later on (and vice versa).
ad (iv): Tetanus (Lockjaw) is a good example of a germ which resides in the soil and which is introduced into the tissues of the animal through wounds (usually deep punctures, like dog bites). In some cases, one cannot even find the entrance point since the lesion itself might have already healed over.
ad (v): It is known that ticks can transmit diseases in both farm animals and pets (eg Babesiosis). Also biting flies have been implicated in the transmission of serious diseases such as Anthrax.
ad (vi): Infection can also be the result of consumption of contaminated natural and/or artificial feedstuffs. Bone meal, for example, has been implicated in several disease outbreaks. And need I mention ‘Mad Cow’ Disease which we know is related to the ingestion of infectious material.
ad (vii):Humans have their share of blame to carry. For example, the docking of dogs’ tails and the surgical intervention associated with castration are well known possibilities of germs entering an animal’s body during the surgery. Animal hospitals and breeding kennels are notorious for harbouring and passing on germs to patients, because their environment, instruments, equipment, and accessories are insanitary.
ad (viii):Many infections (especially bacterial) gain entry into the newborn’s body via the umbilical cord. In dogs and cats, because of their mothers’ care, we don’t see many of these cases. However, if the young pup, for whatever reason, is neglected by its mother, an infection can get into the bloodstream pretty easily. We know of cases where the mother dog’s teeth infect the umbilical cord when she severs it by biting it after the birth of the puppy. In farm animals, a disease of foals, lambs, and calves known as ‘Joint Ill’ or ‘Navel Ill’ takes its toll, if the stump of the umbilical cord is not treated early and correctly.
Lastly, I should mention in passing that animals recovering from a disease (convalescent) may be carriers of viruses for many months, and the viruses may be released continuously or intermittently.
Next week we’ll look at some factors that influence contagious diseases. Stay calm and enjoy your Caricom Day.
Please implement disease preventative measures (vaccinations, routine dewormings, monthly anti-heartworm medication, etc) and adopt-a-pet from the GSPCA’s Animal Clinic and Shelter at Robb Street and Orange Walk, if you have the wherewithal to care well for the animals. Do not stray your unwanted pets, take them to the GSPCA’s Clinic and Shelter instead. If you see anyone being cruel to an animal, or if you need any technical information, please get in touch with the Clinic and Shelter by calling 226-4237.
