18. Co-infections in the Host

Question 1

Co-infection (mixed infection or multi-strain infection):

Answer 1

-when a host is infected with multiple parasite/pathogen species
>or multiple strains of the same parasite/pathogen species
*quite normal

Question 2

Prevalence of multi-strain infections for human pathogens:

Answer 2

-mean prevalence of multi-strain infections is 20% in humans
-some have low prevalence of multi-strain infections (ex. influenza)
-some have high prevalence of multi-strain infections (ex. malaria): >80%

Question 3

Interaction of parasites in a co-infection:

Answer 3

-competition: reduces fitness of the other
-facilitation: enhances fitness of the other

Question 4

Competition vs. facilitation:

Answer 4

-determine abundance of parasite X and parasite Y when they are alone in the host
-determine abundance of parasite X and Y when they co-infect the same host

Question 5

Facilitation:

Answer 5

-abundance in co-infected host will be GREATER than abundance when alone in host

Question 6

Competition:

Answer 6

-abundance in co-infected host will be LESS than abundance when alone in host

Question 7

Ecological niche:

Answer 7

-conditions and resources organism requires to exist

Question 8

Niche overlap:

Answer 8

-2 species have similar niches (ex. host tissues, host resources)
-causes competition over limited resources
>strength depends on the overlap

Question 9

What is the relationship between genetic relatedness of parasites, niche overlap and strength of competition?

Answer 9

-strains of the same parasite species are more likely to have a HIGHER degree of niche overlap
-parasites from different taxonomic groups and/or occupy different tissues are less likely to have niche overlap

Question 10

Co-infection and competition between pathogen strains:

Answer 10

-can reduce their transmission success

Question 11

Competition between tick borne, B afzelii in rodent host (causes LD):

Answer 11

-influence prevalence of each strain in rodent host tissues?
-if competition in rodent host influenced strain transmission to feeding ticks?

Question 12

Experimental design for measuring competition:

Answer 12

-FIN and a CH (Switzerland) strain
-10 mice in each group (40 total)
1. FIN and FIN+CH
2. CH and CH+FIN

Question 13

Competition between FIN and CH:

Answer 13

-FIN strain was negatively affected by CH strain
>FIN was 75% of tissue when alone
>FIN was in 37.5% of tissues when co-infected
-CH not affected by FIN
>CH was around 87.5% of tissues

Question 14

Competition influences strain transmission: FIN and CH

Answer 14

-host-to-tick transmission success
>FIN alone: 90%
>FIN in competition: reduced to 60%
*evidence that FIN experienced competition and reduced strain-specific transmission success

Question 15

HIV prevalence and TB incidence:

Answer 15

-HIV prevalence is positively correlated with TB incidence
*country with high HIV prevalence have high incidence of TB
*due to HIV suppressing the immune system and making the human more susceptible to TB

Question 16

HIV increases susceptibility to TB:

Answer 16

-HIV positive miners: 2.90/100 person-years at risk
-HIV negative miners: 0.80/100 person-years at risk
*risk of getting TB was 3.6x higher for HIV positive miners
*example of facilitation

Question 17

HIV is a driver of TB epidemic in USA:

Answer 17

-number of TB was declining and the began to increase
>attributed to the worsening of the HIV epidemic
*HIV facilitates TB in human populations
*increases the R0 of TB

Question 18

Incident TB cases and TB-related deaths:

Answer 18

-HIV-associated TB contributes disproportionately to TB-related deaths
>15% of incident of TB but 29% of deaths among incident TB cases

Question 19

CFR for TB:

Answer 19

-TB alone: 16%
-TB-HIV co-infection: 37%
*presence of HIV doubled the CFR
*example of how co-infection with multiple pathogens can worse disease outcomes

Question 20

Bovine respiratory disease (BRD):

Answer 20

-“shipping fever”
-occurs in young calves entering commercial feedlots
-75% morbidity
-50-70% of mortality in feedlots
-costs US cattle industry $1B

Question 21

BRD caused by:

Answer 21

-complex of viral and bacterial pathogens linked to stressors associated with management
>traditional view was primary viral infection followed by secondary bacterial infection

Question 22

Stress on feedlot for calves (9-11monts):

Answer 22

-separation
-transport
-new social environment
*suppress the immune system

Question 23

What facilitates pathogen exposure and transmission: feed lots

Answer 23

-high density and comingling
>during transport and at feedlots

Question 24

BRD associated with:

Answer 24

-viruses
-bacteria
-nematode parasites
*Bovine viral diarrhea virus (BVDV)
*Mannheimia haemolytica
*Mycoplasma bovis

Question 25

What results in BRD in feedlots?

Answer 25

-stress
-suppressed immune system
-high density
-exposure to many pathogens

Question 26

BRD pathology and viruses:

Answer 26

-calves died within 60days of entering feedlot
-classified into 5 categories

Question 27

Most common agents in fatal BRD cases

Answer 27

-Mannheimia haemolytica
-mycoplasma bovis
*difficult to assign causality as immunohistochemistry (IHC) only gives presence/absence of pathogens not their ABUNDANCE in the lungs

Question 28

BRD clinical signs:

Answer 28

-depression
-reluctance to move
-abnormal posture
-rectal temperature over 40.5C

Question 29

Testing to determine BRD bacteria present in sick and healthy cattle:

Answer 29

-nasopharyngeal swabs to sample bacterial microbiome
-16S rNA sequencing to determine bacterial diversity
*Mycoplasma bovis and Mannheimia haemolytica were found in BOTH

Question 30

Bovine viral diarrhea virus (BVRD):

Answer 30

-associated with BRD
-results in persistently infected and acutely affected calves
>both have higher incidence of BRD
-suppresses immune system
-kills lymphocytes and reduces their function
*makes animals susceptible to other pathogens

Question 31

BVRD and BRD:

Answer 31

-6 PI. Calves
>4 pens, 9 out of 20 pens were considered exposed to BVRD
-risk for initial treatment of BRD was 43% higher in those exposed to BVRD
*study suggestion BVDV facilitates BRD
>limitation: no testing of respiratory pathogens in the lungs

Question 32

Summary of BRD in cattle:

Answer 32

-most important disease in NA
-based on clinical symptoms
-associated with several viral and bacterial pathogens
-stress and viral infection suppress immune system=*drives bacterial dysbiosis in respiratory tract which causes BRD

Question 33

African buffalo:

Answer 33

-are naturally infected with GI nematodes
-also infected with M. bovis which causes BTB (in the respiratory tract)
*many have co-infections

Question 34

Buffalo fitness:

Answer 34

-parasites have negative effects on host fitness
-body condition=amount of body fat on buffalo

Question 35

4 groups in buffalo study:

Answer 35

1. Worm alone
2. TB alone
3. Worm and TB (*lowest body condition)
4. Uninfected

Question 36

Worm infection and body condition of buffalo:

Answer 36

-associated with poor body condition in TB positive
>but not in TB negative
*co-infected buffalo have a lower body condition
*synergistic effect

Question 37

Synergistic effects:

Answer 37

-whole is greater than sum of its parts

Question 38

De-worming African buffalo and BTB:

Answer 38

-control group and deworming treatment group
>nematode prevalence was the same at the start
>deworming was with anthelmintic and it was effective
>*all were BTB negative at start

Question 39

De-worming study, after the 4 years:

Answer 39

-1/3 of buffalo had acquired BTB
>prevalence was similar between de-wormed and control groups
*GI worms did NOT influence susceptibility of buffalo to BTB

Question 40

Compared survival of BTB-infected buffalo in dewormed and control groups:

Answer 40

-mortality rate of control group was 9x higher than dewormed
*GI nematodes increase mortality rate of BTB-infected buffalo

Question 41

Does higher survival of BTB-infected animals benefit the buffalo population?

Answer 41

-not necessarily
>now have infected individuals surviving and potentially infecting others

Question 42

R0 of M. bovis in control and dewormed buffalo:

Answer 42

-8x higher in treated than control buffalo
>de-worming allows TB buffalo to live a long life=enhances TB transmission
*de-worming increased R0 of TB in buffalo population

Question 43

De-worming buffalo outcome:

Answer 43

-bad
>increases TB transmission and prevalence
*increased R0

Question 44

High cost of co-infection of BTB and worms:

Answer 44

*co-infected individuals die quickly which reduces BTB transmission
*what is good for the individual and what is good for the population are often in conflict