Disease Triad: Hosts

Host

an animal, human, or plant that harbors and provides sustenance for another organism

Contagious

capable of being transmitted from animal to animal, human to human, human to animal, or animal to human

Resistance

the ability of an organism to remain unaffected by noxious agents/pathogens in its environment

Susceptibility

the state of being likely or liable to be influenced or harmed by a particular thing (i.e. disease agent)

Immunity

the capacity to distinguish material from self, and to neutralize that which is foreign

What are the six host factors

• species

• sex

• genetics

• life stage

• host response

• nutrition

What about species do we consider in terms of host factors?

• anatomic differences

• physiologic differences

• metabolic differences

• genetic difference

How does rabies vary by species?

It is a virus that only affects warm blooded mammals, but it is also highly sensitive to temperature. That’s why the raccoon, with a body temp of 102.8 F is more likely to acquire it than an opposum with a body temp of 95.8 F

This is an example of how species’ physiologic differences are a host factor

What about sex do we consider in terms of host factors?

• anatomical differences

• hormonal differences

• behavioral differences

How does struvite urolithiasis affect canine sexes differently?

• females have more cases of struvite crystalluria

• males have more cases of struvite urethral obstruction

• length of the urinary tract has an impact

What about genetics do we consider in terms of host factors?

• species differences

• breed differences

• genetic disorders

What about life stage do we consider in terms of host factors?

• neonates

• juveniles

• adults

• elderly

• whether the animal is breeding, pregnant, or lactating

Neonates

• lack of immunity

  • must consume colostrum to acquire immune globulins

    • exception: primates

• lack of essential nutrients

Juveniles

• predisposed to certain diseases

  • ex.

    • Blackleg (clostridial myositis)

      • rarely seen in cattle < 4 mo

      • rarely seen in cattle > 2 yr

Elderly

• prone to degenerative diseases

• prone to cancers

• greater risk of infectious disease

  • impaired immunity

Adult

• generally the most resistant to disease

• reproductive status can greatly impact disease

Reproductive status

• breeding

  • sexually transmitted infections

  • males - injury/fighting

• pregnancy

  • immune suppression

    • greater risk of certain infectious diseases

  • metabolic challenges of pregnancy

    • may result in nutritional/metabolic disorders

• lactation

  • new avenue for infection

    • mastitis

  • metabolically challenging

Hereditary

derived from ancestry; in the genome, can be passed generation to generation

Congenital

• existing at birth

  • may be hereditary

  • may be acquired during gestation

    • infectious or environmental origin

Familial

• occurring among members of the same family

  • may be hereditary or acquired

Lethal

• a condition that is incompatible with life

  • death may occur ante- or post-natally

Sublethal

a condition that is undesirable, but in itself does not usually result in death

What about host responses do we consider in terms of host factors?

• the following influence resistance and susceptibility to a disease

  • stress

  • inflammation

  • immune response

What about nutrition do we consider in terms of host factors?

• intake

• nutrient balance

• feed and water quality

Starvation

• complete deprivation of feed (anorexia)

  • acute vs. chronic adaptation

  • duration impacts severity of tissue mobilization

Inanition

• reduced feed intake (hypophagia)

  • suboptimal feed intake for a variety of reasons

  • similar response as starvation, just not as severe

Causes of inadequate intake

• lack of feed availability

• inability to consume sufficient food

• inability to assimilate food consumed

Overfeeding

• aka hyperphagia → obesity (number one nutritional issue in pets)

  • over supply of nutrients relative to requirement

  • excess energy intake leads to obesity

  • nutrient interactions leading to deficiency or toxicity disease

Pica

• depraved appetite

  • eating of abnormal items: soil, bones, sticks, stones, urine pool, etc.

  • underlying nutritional deficiency (P, Fe, Na, K)

  • learned behavior behavior or boredom

  • a physiologic disease that can lead to learned behaviors

Essential nutrients

• water - quality, availability

• energy (CHO, fats, protein)

• amino acids (protein)

• fatty acids - omega 3 and 6 sources

• minerals

  • macro: Ca, P, Mg, K, Na, Cl, S

  • micro: Co, Cu, Fe, I, Mn, Se, Zn

• vitamins (fat- and water-soluble)

• fiber - to maintain microbes, gut health

Management factors to consider

• feeding facilities

  • feed bunk space

  • stocking density

  • water availability

• feeding management

  • feed preparations

  • delivery of feed - times, amounts, consistency