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Disease Epidemiology #2 > Co-infections in the host > Flashcards

Co-infections in the host Flashcards

1
Q

Co-infection

A
  • When a host is infected with multiple pathogen species
  • OR when host is infected with multiple strains of the same pathogen species
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2
Q

Host species and number of pathogen species

A
  • Each host species is infected with many different pathogen species
    o Often a host organism can be infected with multiple pathogen species at the same time therefore co-infections with different pathogens are the norm

Ex. rodent host has 18 different pathogens (bacteria, protozoans, nematodes, cestodes, fleas, ticks)

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3
Q

Prevalence of multi-strain infections for human pathogens

A
  • Study on prevalence of multi-strain infections for 62 human pathogens
  • Mean prevalence of multi-strain infections in humans is 20%
    »Some pathogens have low prevalence of multi-strain infections (eg. Influenza)
    » Some pathogens have high prevalence of multi-strain infections (eg. Malaria)
  • Overall, multi-strain pathogens are common
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4
Q

Co-infection and parasites

A

Co-infected hosts carry multiple parasite species or parasite strains which leads to these pathogens interacting inside the host

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5
Q

Interactions between pathogens

A
  1. Competition- parasite A reduces fitness of parasite B (and/or vice versa)
  2. Facilitation (cooperation)- parasite A enhances fitness of parasite B (and/or vice versa)
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6
Q

How do you determine whether the pathogen interaction is competition or facilitation?

A

Determine the abundance of each of the pathogens when they are alone in the host, and when they are together in the host
- Facilitation: abundance in co-infected host will be greater than abundance when alone in the host
- Competition: abundance in co-infected host less than abundance when alone in the host

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7
Q

Ecological niche

A

Conditions and resources organism requires to exist

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8
Q

Competition and niche overlap

A
  • When 2 species have similar niches (host tissues, host resources) it results in competition over limited resources
  • The strength of the competition depends on the degree of niche overlap
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9
Q

B. afzelii in rodent host

A
  • tick-borne pathogen where competition between strains exists
  • Look at FIN strain (finnish) and CH (NE4049/swiss) strain
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10
Q

Competition between B. afzelii strains

A
  • Fin was negatively affected by CH
    o When alone, it was found in 75% of tissues but when co-infected, found in less than 37.5%
  • CH strain was not affected by presence of FIN
    o In absence or presence of competition, Swiss strain infected 87.5% of tissues
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11
Q

Competitions effect on strain transmission

A
  • FIN strain when alone had greater than 90% transmission
  • Presence of swiss strain reduced transmission of FIN strain to 60%
  • Reduction of transmission is evidence of competition therefore co-infection and competition leads to a reduction of transmission success
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12
Q

HIV prevalence and TB incidence

A

HIV prevalence rates are positively correlated with TB incidence
- Countries with high prevalence of HIV have high incidence of TB

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13
Q

What causes the positive correlation between HIV prevalence and TB incidence?

A

HIV is primary and depletes host immune system which makes them susceptible to TB

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14
Q

HIV and TB in miners study

A
  • Looked at group of miners where 14.1% were HIV positive
  • Calculated incidence rate for HIV positive and HIV negative miners
    »HIV positive: 2.90 cases/100 person years at risk
    »HIV negative: 0.80 cases/100 person-years at risk
  • HIV increases susceptibility of humans to acquire TB (Facilitation)
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15
Q

HIV driving TB epidemic in USA

A
  • HIV is driver of TB population
  • Epidemic (~51,700 excess TB cases)
  • HIV makes it easier for TB to spread through human populations
  • Presence of HIV increases the R0 of TB
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16
Q

TB human death rates

A
  • HIV associated TB contributes disproportionately to TB related deaths.
  • Case fatality rate for patients with just TB= 16%
  • Case fatality rate for patients are co-infected with TB and HIV= 37%
  • Shows how co-infection with multiple pathogens can worse the disease outcome
17
Q

Bovine respiratory disease (BRD)

A
  • Also called shipping fever
  • Occurs in young calves entering commercial feedlots
  • 75% morbidity and 50-70% mortality in feedlots
  • Costs US cattle industry ~1 billion USD per year
  • Caused by complex of viral and bacterial pathogens linked to stressors associated with management
18
Q

Traditional view of Bovine respiratory disease

A

Primary viral infection followed by secondary bacterial infection

19
Q

Stress at feedlots

A
  • Beef calves (9-11 months old) are separated from moms and transported to feedlots
    o Separation
    o Transport
    o New social environment
  • Stress suppresses calf immune system.
  • High density and comingling during transport and at feedlot facilitates pathogen exposure and transmission
20
Q

Some main viruses and bacteria that are associated with Bovine respiratory disease

A
  • Bovine viral diarrhea virus (BVDV)
  • Mannheimia haemolytica
  • Mycoplasma bovis
  • Difficult to know true causation because there are so many associated viruses and bacteria
21
Q

Bovine respiratory disease study in Western Canada

A
  • Study in 90 feedlot calves in western Canada that were classified into 5 categories. Calves died within 60 days of entering the feedlot
  • Immunohistochemistry provides presence/absence of pathogens (but not abundance) and found Mannheimia haemolytica and mycoplasma bovis were most common in fatal BRD cases, but others present as well
  • Makes it difficult to assign causality
22
Q

Bacterial microbiomes of bovine respiratory disease positive individuals compared with healthy ones

A
  • Positive if they displayed clinical signs (depression, reluctance to move, abnormal posture, rectal temp greater than 40.5)
  • Took nasopharyngeal swabs to sample bacterial microbiome and 16S rRNA sequencing
    »Saw a violation of Koch’s postulates because both sick and healthy individuals had the same bacteria specifically Mycoplasma bovis and Mannheimia hemolytica
  • Seems that all bacteria present but when sick, different abundances must occur
23
Q

Bovine viral diarrhea virus (BVDV) and Bovine respiratory disease (BRD)

A
  • Bovine viral diarrhea virus is associated with bovine respiratory disease
    »BVDV suppresses cattle immune system. Kills lymphocytes and reduces function.
  • BVDV results in persistently infected and acutely infected calves which act as super spreaders
24
Q

Test whether Bovine viral diarrhea virus increases risk of bovine respiratory disease in feedlots

A
  • 2000 calves in 20 pens
  • 6 persistently infected calves (BVDV)
  • Exposed 9 pens to BVDV and 11 pens were not exposed
  • Study showed that risk of bovine respiratory disease was 43% higher in calves exposed to persistently infected individuals (bovine viral diarrhea virus) showing that BVDV facilitates BRD
25
Q

Limitations to BVDV and BRD experiment

A
  • No testing of respiratory pathogens in the lungs
26
Q

African buffalo, TB and nematode parasites

A

Many buffalo have co-infections with GI nematodes and M. bovis which causes TB (found in GI tract not respiratory tract)

27
Q

Effect of worms in TB-infected buffalo

A
  • Parasites have negative effects on host/buffalo fitness (body condition is reduced/less body fat) when host is TB positive but not when they are TB negative
    »Worms and TB results in poor BCS
  • Parasites have synergistic effects where the whole is greater than sum of its part
28
Q

De-worming African buffalo and bovine TB

A
  • Had 200 buffalo, one control and other group were dewormed
  • At start prevalence of worms was the same between the two groups
  • All buffalo were TB negative at start of study. At end of study 1/3 of individuals were TB positive
  • Prevalence of TB was similar in the de-wormed group and control group which told us that the GI worms did not influence the buffalo susceptibility. (different than miners with HIV and TB)
29
Q

Survival of dewormed and control buffalo

A
  • Dewormed individuals with TB had great survival.
  • Control group with no dewormer and TB had lower survival rate (9x higher)

Therefore GI nematodes increase mortality rate of TB infected buffalo BUT this means that there are buffalo living with TB staying in population**

30
Q

R0 of TB infected buffalo after being dewormed

A

Deworming led to increase survival rate of TB infected buffalo because got rid of GI parasites. This led to 8x higher R0 so an increased TB transmission
- So deworming led to a counterintuitive outcome where TB transmission and prevalence increased
»>What is good for the individual and what is good for the population are often in conflict

Disease Epidemiology #2 (11 decks)

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